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. 2022 Sep 23;9(10):ofac493. doi: 10.1093/ofid/ofac493

Correlation of Postvaccination Fever With Specific Antibody Response to Severe Acute Respiratory Syndrome Coronavirus 2 BNT162b2 Booster and No Significant Influence of Antipyretic Medication

Naoki Tani 1, Hideyuki Ikematsu 2, Takeyuki Goto 3, Kei Gondo 4, Takeru Inoue 5, Yuki Yanagihara 6, Yasuo Kurata 7, Ryo Oishi 8, Junya Minami 9, Kyoko Onozawa 10, Sukehisa Nagano 11, Hiroyuki Kuwano 12, Koichi Akashi 13, Nobuyuki Shimono 14, Yong Chong 15,✉,2
PMCID: PMC9578158  PMID: 36267253

Abstract

Background

A severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mRNA vaccine booster elicits sufficient antibody responses that protect against coronavirus disease 2019, whereas adverse reactions such as fever have been commonly reported. Associations between adverse reactions and antibody responses have not been fully characterized, nor has the influence of antipyretic use.

Methods

This is a prospective observational cohort study in Japan, following our prior investigation of BNT162b2 2-dose primary series. Spike-specific immunoglobulin G (IgG) titers were measured for SARS-CoV-2–naive hospital healthcare workers who received a BNT162b2 booster. The severity of solicited adverse reactions, including the highest body temperature, and self-medicated antipyretics were reported daily for 7 days following vaccination through a web-based self-reporting diary.

Results

The data of 281 healthcare workers were available. Multivariate analysis extracted fever after the booster dose (β = .305, P < .001) as being significantly correlated with the specific IgG titers. The analysis of 164 participants with data from the primary series showed that fever after the second dose was associated with the emergence of fever after the booster dose (relative risk, 3.97 [95% confidence interval, 2.48–6.35]); however, the IgG titers after the booster dose were not associated with the presence or degree of fever after the second dose. There were no significant differences in the IgG titers by the use, type, or dosage of antipyretic medication.

Conclusions

These results suggest an independent correlation between mRNA vaccine–induced specific IgG levels and post–booster vaccination fever, without any significant influence of fever after the primary series. Antipyretic medications for adverse reactions should not interfere with the elevation of specific IgG titers.

Keywords: antipyretic, antibody, reactogenicity, SARS-CoV-2, vaccine


Spike-specific IgG titers after a BNT162b2 booster were measured for healthcare workers. Adverse reactions and self-medicated antipyretics were reported. Post–booster vaccination fever was correlated with the specific IgG titers. Antipyretics used for adverse reactions did not suppress specific IgG induction.


Administration of a messenger RNA (mRNA) coronavirus disease 2019 (COVID-19) vaccine has shown high vaccine efficacy, substantially reducing the risk of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and the development of severe or critical disease [1–4]. These efficacy data are consistent with evidence from immunogenicity studies that show robust specific antibody responses to the mRNA COVID-19 vaccines [5, 6]. It is notable that the specific immunoglobulin G (IgG) and neutralization titers of vaccinees who received an mRNA COVID-19 vaccine exceeded those of recovered COVID-19 patients [7, 8]. On the other hand, the reactogenicity of mRNA COVID-19 vaccines is known to be relatively high, and fever is a common adverse reaction. Around 15% of vaccinees had fever after the second or third dose of an mRNA COVID-19 vaccine [1, 9, 10], while only 1%–2% did so after influenza or pneumococcal vaccination [11, 12]. The possible relation between adverse reactions, including fever, and the antibody responses to mRNA COVID-19 vaccines remains to be fully elucidated. Antipyretic or pain medications (antipyretics) are often used to mitigate the frequent adverse events. Public health authorities allow the use of antipyretics in response to adverse events [13, 14], but data for the possible influence of their use on the antibody responses to COVID-19 vaccines are insufficient.

We previously investigated the correlation of adverse reactions with the specific antibody responses to the 2-dose primary series of BNT162b2 vaccine (Pfizer/BioNTech). The influence of antipyretic use on antibody responses was also investigated. A positive correlation of degree of fever after the second dose and little interference from the antipyretic medications on the antibody titers were shown [15]. In the present study of the same cohort, we prospectively investigated the association of adverse reactions, which were evaluated using a standardized assessment tool, and the use of antipyretics with the specific antibody responses to a booster dose of BNT162b2 vaccine. In addition, using the data of the participants for whom information on both the second and booster doses was available, we also evaluated whether the specific antibody titers after the booster dose are affected by fever after the second dose.

METHODS

Participants

Eligible participants were healthcare workers who received three 30-µg doses of BNT162b2 at Fukuoka City Hospital in Japan. The primary 2-dose vaccine series with a 21-day interval was administered between March and June 2021, and the booster dose was given between December 2021 and January 2022. Included in the analysis were vaccinees who had serum sampling done ≥14 days after the booster dose and who completely responded to questionnaires about their background and solicited adverse reactions. The exclusion criteria were (1) previous laboratory-confirmed COVID-19 diagnosis, (2) positive results for antibodies targeting the viral nucleocapsid protein [IgG(N)], (3) the use of an antipyretic within 24 hours before the booster dose, and (4) receipt of immunosuppressive therapy.

Participant Consent Statement

All participants provided written informed consent before undergoing any of the study procedures. The study was approved by the ethics review board of Fukuoka City Hospital (approval number 228) and registered in the University Hospital Medical Information Network Clinical Trials Registry (registration number UMIN000046246).

Demographic Characteristics, Reactogenicity, and Antipyretic Medications

Participant background information was collected by a web-based questionnaire. Local and systemic adverse reactions were reported daily for 7 days after the booster dose through a web-based self-reporting diary. The solicited data were as follows: (1) local reactions (pain at the injection site, redness, and swelling) and (2) systemic events (fever, fatigue, headache, chills, vomiting, diarrhea, muscle pain, joint pain, and lymphadenopathy). Axillary body temperature was measured twice daily, morning and night, and whenever the participant felt feverish. The highest body temperature during the 7 days was used in the analysis. All solicited reactions except lymphadenopathy were recorded based on standardized assessment scales developed by the US Food and Drug Administration guidelines [16]. Lymphadenopathy was evaluated for its presence or absence. The use of an antipyretic was left up to the participant. Information on the self-medicated antipyretics, including name, dosage, timing, and reason for use, was collected daily with the solicited adverse reactions for the 7 days after the booster dose.

Previously collected data on the receptor-binding domain of the S1 subunit of the viral spike protein (S-RBD) IgG titers and adverse reactions to the second dose were used in the present study. The major differences in the method of data collection were that in the earlier studies the adverse reaction information was collected for 5 days, not 7, after each of the doses and that we had used an originally defined subjective scaling method, except for fever. The detailed methods are shown in our previous study [15].

Serological Testing

Serum samples were collected twice, before and after the booster dose. The interval between the booster dose and the sampling after vaccination was scheduled at approximately 1 month to match it with the interval between the second dose and the sampling [15]. The quantitative levels of IgG(S-RBD) and IgG(N) were measured using the SARS-CoV-2 IgG II assay and SARS-CoV-2 IgG assay, respectively (Abbott Laboratories, Abbott Park, Illinois). Signal-to-cutoff values of ≥1.4 AU/mL were applied for IgG(N) positivity [17].

Statistical Analysis

The IgG(S-RBD) titers were log-transformed for analysis. The median with interquartile range (IQR), geometric mean titer (GMT), fold change, 95% confidence interval (CI), and relative risk (RR) were calculated. Between-group differences were calculated with Student t test, analysis of variance, or post hoc Dunnett test in line with suitability. Correlation coefficients were calculated using Spearman correlation coefficient. Multivariate linear regression models with a stepwise selection procedure were established. Multicollinearity among variables was examined using variance inflation factors. The level of significance was set at <5%, 2-sided. All analyses were performed using the SAS software package, release 9.4 (SAS Institute, Cary, North Carolina).

RESULTS

Demographic Characteristics

Among 419 staff members who received the BNT162b2 booster, serum samples were collected from 346, and 316 satisfied the inclusion criteria. Of these, 13 were excluded due to a history of COVID-19 or IgG(N) ≥1.4 AU/mL, 20 due to prevaccination use of antipyretics, and 2 due to having received immunosuppressive therapy, leaving the data of 281 participants available for analysis. Demographic and background information are summarized in Table 1. The median age was 41 years (IQR, 33–50 years), 72.6% were female, all were Japanese, and 77.2% had no coexisting conditions. The median interval between the second and booster doses was 262 days (IQR, 260–264 days; range, 219–288 days). Serum samples before and after the booster dose were obtained approximately 8 months after the second dose (median, 247 days [IQR, 244–252 days]) and 1 month after the booster dose (median, 32 days [IQR, 29–33 days]), respectively.

Table 1.

Demographic Characteristics, Spike Receptor-Binding Domain Immunoglobulin G Titer, and Fold Change

Characteristic No. (%) IgG(S-RBD) Titers Before Dose 3 IgG(S-RBD) Titers After Dose 3 Change in Titers After Dose 3
GMT (95% CI), AU/mL P Value GMT (95% CI), AU/mL P Value Fold Change, Mean (95% CI) P Value
All eligible participants 281 573 (528–621) 16 707 (15 403–18 122) 29.4 (26.7–32.5)
Sex
 Female 204 (72.6) 602 (546–665) .047 16 110 (14 743–17 604) .197 26.7 (24.4–29.3) <.001
 Male 77 (27.4) 502 (436–577) 18 395 (15 325–22 085) 36.7 (31.1–43.3)
Age, y
 Median (IQR) 41 (33–50) r = –0.215a <.001 r = 0.009a .877 r = 0.231a <.001
 <40 127 (45.2) 648 (582–723) .014 16 970 (15 199–18 948) .509 26.2 (23.4–29.3) .006
 40–54 118 (42.0) 534 (472–603) 15 937 (14 055–18 072) 29.9 (26.2–34.0)
 ≥55 36 (12.8) 468 (345–634) 18 453 (13 623–24 995) 39.5 (30.7–50.7)
Smoking
 Never 234 (83.3) 602 (549–659) .030 17 249 (15 747–18 894) .134 28.7 (26.2–31.4) .473
 Ex-smoker 26 (9.3) 457 (385–543) 15 627 (12 922–18 899) 34.2 (27.8–42.1)
 Current smoker 21 (7.5) 441 (321–605) 12 713 (9214–17 540) 28.8 (21.3–39.1)
Alcohol use
 None 113 (40.2) 598 (523–684) .493 17 781 (15 604–20 261) .465 29.7 (26.4–33.4) .698
 Sometimes 136 (48.4) 569 (510–634) 16 048 (14 358–17 937) 28.2 (25.0–31.8)
 Almost every day 32 (11.4) 508 (378–682) 15 907 (11 890–21 282) 31.3 (23.0–42.5)
BMI, kg/m2
 Median (IQR) 21.2 (19.7–23.3) r = –0.032a .599 r = .091a .130 r = .137a .022
 <18.5 26 (9.3) 531 (373–758) .417 15 055 (11 162–20 307) .545 27.2 (20.7–35.7) .079
 18.5–24.9 220 (78.6) 589 (539–645) 16 666 (15 268–18 192) 28.3 (25.8–31.0)
 ≥25.0 34 (12.1) 506 (408–682) 18 332 (15 695–24 540) 39.9 (32.2–44.5)
Job category
 Nurse 140 (49.8) 575 (516–641) .483 15 704 (14 270–17 283) .488 27.3 (24.7–31.2) .061
 Clerk 40 (14.2) 648 (507–828) 15 731 (12 771–19 378) 24.3 (18.8–31.3)
 Doctor 30 (10.7) 467 (362–602) 17 364 (12 091–24 936) 37.2 (27.3–50.7)
 Radiologist 13 (4.6) 605 (438–837) 19 694 (12 239–31 690) 32.5 (17.7–59.8)
 Pharmacist 12 (4.3) 652 (389–1093) 19 696 (14 270–17 283) 30.2 (18.3–49.9)
 Other 46 (16.4) 555 (443–694) 18 953 (15 130–23 742) 34.2 (28.4–41.1)
Comorbidities
 Allergic rhinitis
  Yes 43 (15.3) 537 (448–645) .508 14 801 (11 989–18 277) .213 27.6 (23.2–32.7) .563
  No 238 (84.7) 580 (530–635) 16 963 (15 513–18 548) 29.4 (26.7–32.5)
 Dislipidemia
  Yes 17 (6.1) 656 (464–929) .405 20 333 (12 526–33 007) .381 31.0 (21.7–44.3) .710
  No 264 (94.0) 568 (522–618) 16 497 (15 205–17 898) 29.0 (26.7–31.6)
 Hypertension
  Yes 14 (5.0) 455 (262–790) .364 12 314 (6393–23 719) .313 27.1 (18.0–40.7) .683
  No 267 (95.0) 580 (535–629) 16 975 (15 678–18 382) 29.3 (26.9–31.8)
 Asthma
  Yes 5 (1.8) 798 (470–1352) .281 21 154 (11 389–39 292) .442 26.5 (15.4–45.8) .759
  No 276 (98.2) 570 (525–618) 16 634 (15 321–18 063) 29.2 (26.9–31.7)
 Diabetes
  Yes 3 (1.1) 439 (96–2004) .504 41 850 (14 723–118 987) .021 95.3 (56.1–162.0) .003
  No 278 (98.9) 575 (529–624) 16 542 (15 251–17 943) 28.8 (26.5–31.2)
 Heart disease
  Yes 3 (1.1) 539 (324–894) .876 33 411 (3446–323 966) .081 62.0 (6.1–632.8) .058
  No 278 (98.9) 573 (528–622) 16 581 (15 290–17 985) 28.9 (26.7–31.4)
 Malignancy
  Yes 3 (1.1) 460 (45–4648) .581 19 838 (1219–322 849) .666 43.1 (3.7–497.3) .327
  No 278 (98.9) 574 (529–623) 16 676 (15 374–18 088) 29.0 (26.8–31.5)
 Chronic kidney disease
  Yes 1 (0.4) 626 (NA) NA 32 300 (NA) NA 51.6 (NA) NA
  No 280 (99.4) 573 (528–621) 16 669 (15 364–18 080) 29.1 (26.8–31.6)

Abbreviations: BMI, body mass index; CI, confidence interval; GMT, geometric mean titer; IgG(S-RBD), immunoglobulin G spike receptor-binding domain; IQR, interquartile range; NA, not available.

a

r values refer to the Spearman correlation coefficient.

IgG(S-RBD) Titer and Fold Change by Demographic Characteristics

The booster dose increased the GMT of IgG(S-RBD) 29.4-fold (95% CI, 26.7–32.5), from 573 AU/mL (95% CI, 528–621) to 16 707 AU/mL (95% CI, 15 403–18 122). The IgG(S-RBD) titers and fold changes according to demographic characteristics are shown in Table 1. In the analysis of the IgG(S-RBD) titers, sex and age showed no significant correlation (P = .197 and P = .645, respectively). In contrast, both were significantly correlated with the fold changes. The mean fold change in males was higher than that in females (36.7-fold [95% CI, 31.1–43.3] vs 26.7-fold [95% CI, 24.4–29.3]; P < .001). Age showed a positive correlation with the fold changes (r = 0.244, P < .001). Comorbidities other than diabetes were not correlated. Diabetes had statistically significant correlations with both the IgG(S-RBD) titers and fold changes, but it was not further analyzed due to the small number of participants with diabetes.

IgG(S-RBD) Titer and Fold Change by Adverse Reaction

The IgG(S-RBD) titers and fold changes after the booster dose by the solicited adverse reactions are shown in Table 2. None of the local reactions had a significant correlation with the IgG(S-RBD) titers. Among the systemic reactions, fever showed a positive correlation with the IgG(S-RBD) titers (r = 0.262, P < .001). Fatigue (P = .022), headache (P = .024), chills (P = .001), and lymphadenopathy (P < .001) were also positively correlated. Neither local nor systemic adverse reactions significantly affected the fold changes in IgG(S-RBD) titers.

Table 2.

Influence of Adverse Reaction Variables on Spike Receptor-Binding Domain Immunoglobulin G Titer

Reaction Variable No. (%) GMT (95% CI), AU/mL P Value Fold Change, Mean (95% CI) P Value
Local reactions
 Pain at injection site No 3 (1.1) 14 818 (4032–54 450) .763 23.9 (10.9–52.4) .618
Yes 278 (98.9) 16 730 (15 413–18 155) 29.2 (26.9–31.7)
 Redness No 185 (65.8) 16 761 (15 198–18 484) .915 28.9 (26.2–31.9) .734
Yes 96 (34.2) 16 604 (14 328–19 244) 29.7 (25.7–34.4)
 Swelling No 148 (52.7) 16 707 (14 866–18 772) .998 30.5 (27.4–33.8) .269
Yes 133 (47.3) 16 707 (14 907–18 728) 27.8 (24.5–31.6)
Systemic reactions
 Fever Absolute value 281 (100) r = 0.262a <.001 r = 0.082a .170
<37.0°C 114 (40.6) 14 011 (12 431–15 793) <.001 26.9 (23.7–30.5) .100
37.0°C–37.9°C 97 (34.5) 16 302 (14 174–18 750) 28.8 (25.3–32.9)
≥38.0°C 64 (24.9) 23 020 (19 670–26 941) 33.7 (28.1–40.5)
 Fatigue No 42 (15.0) 13 329 (10 713–16 581) .022 26.2 (20.8–32.9) .278
Yes 239 (85.1) 17 382 (15 933–18 967) 29.7 (27.2–32.4)
 Headache No 94 (33.5) 14 652 (12 885–16 661) .024 29.3 (25.6–33.5) .947
Yes 187 (66.6) 17 848 (16 099–19 783) 29.1 (26.3–32.3)
 Chills No 135 (48.0) 14 534 (13 077–16 151) .001 27.3 (24.3–30.7) .126
Yes 146 (52.0) 19 006 (16 862–21 419) 31.0 (27.6–34.8)
 Vomiting No 272 (96.8) 16 512 (15 198–17 943) .121 29.1 (26.7–31.6) .721
Yes 9 (3.2) 23 752 (16 021–35 221) 31.6 (22.5–44.5)
 Diarrhea No 246 (87.5) 16 811 (15 385–18 365) .693 29.3 (26.8–32.0) .812
Yes 35 (12.5) 15 999 (13 005–19 683) 28.4 (23.6–34.2)
 Muscle pain No 40 (14.2) 17 434 (14 142–21 493) .674 28.9 (22.2–37.7) .944
Yes 241 (85.8) 16 588 (15 181–18 126) 29.2 (26.8–31.8)
 Joint pain No 128 (45.6) 16 044 (14 315–17 980) .370 27.9 (24.6–31.6) .335
Yes 153 (54.5) 17 282 (15 396–19 404) 30.2 (27.1–33.7)
 Lymphadenopathy No 194 (69.0) 15 332 (13 845–16 975) <.001 29.1 (26.1–32.4) .956
Yes 87 (31.0) 20 234 (17 857–22 935) 29.2 (26.2–32.7)

Abbreviations: CI, confidence interval; GMT, geometric mean titer.

a

r values refer to the Spearman correlation coefficient.

Factors that showed a P value of <.2 in the univariate analyses, including sex, body mass index, smoking history, heart disease, fever, fatigue, headache, chills, vomiting, and lymphadenopathy, were incorporated in the multivariate analysis. Among these variables, only fever (standardized regression coefficient: β = .305 [95% CI, .193–.417]; P < .001) was extracted as being independently correlated with the IgG(S-RBD) titers (adjusted R2 = 0.090). A similar analysis for the fold change in IgG(S-RBD) titers extracted age (β = .248 [95% CI, .136–.360]; P < .001), male sex (β = .183 [95% CI, .071–.294]; P = .001), and fever (β = .136 [95% CI, .024–.248]; P = .018) as significant (adjusted R2 = 0.105). All variance inflation values were <5 in the linear regression models, indicating the absence of multicollinearity among the factors.

Influence of Antipyretic Medications on IgG(S-RBD) Titer and Fold Change

The analyses of the influence of antipyretics on the IgG(S-RBD) titers and fold changes are shown in Table 3. In total, 119 (42.4%) participants used antipyretics during the 7 days after the booster dose. None of the participants prophylactically used an antipyretic after the vaccination to prevent adverse events. The GMT of IgG(S-RBD) was comparable between the groups with and without antipyretic use (17 466 AU/mL [95% CI, 15 279–19 966] vs 16 170 AU/mL [95% CI, 14 601–17 906]; P = .357). Similarly, there was no significant difference in the mean fold change between the 2 groups (29.4-fold [95% CI, 26.1–33.2] vs 28.9-fold [95% CI, 25.9–32.4]; P = .893). No significant influence of antipyretic use was found when stratified by fever grade, classified into <37.0°C, 37.0°C–37.9°C, and ≥38.0°C. The most commonly used antipyretic combination was acetaminophen monotherapy (43/119 [36.1%]), followed by loxoprofen monotherapy (35/119 [29.4%]) and ibuprofen monotherapy (14/119 [11.8%]). The IgG(S-RBD) titers and fold changes of the group with nonsteroidal anti-inflammatory drugs (NSAIDs) such as loxoprofen and ibuprofen were comparable to those of acetaminophen. The IgG(S-RBD) titers by all combinations of antipyretics used are summarized in Supplementary Table 1.

Table 3.

Influence of Antipyretics on Spike Receptor-Binding Domain Immunoglobulin G Titer and Fold Change After a Booster Dose

Characteristic No. (%) GMT (95% CI) P Value Fold Change, Mean
(95% CI)
P Value
Use of antipyretic medications
 All participants No 162 (57.7) 16 170 (14 601–17 906) .357 28.9 (25.9–32.4) .893
Yes 119 (42.4) 17 466 (15 279–19 966) 29.4 (26.1–33.2)
 By fever grade
  <37.0°C No 85 (74.6) 14 217 (12 491–16 181) .681 27.8 (23.8–32.4) .400
Yes 29 (25.4) 13 425 (10 006–18 009) 24.6 (19.9–30.3)
  37.0°C–37.9°C No 50 (51.6) 16 489 (13 602–19 985) .869 30.0 (24.7–36.4) .556
Yes 47 (48.5) 16 106 (13 041–19 893) 27.7 (23.2–33.2)
  ≥38.0°C No 27 (38.6) 23 388 (17 914–30 542) .874 31.0 (22.4–42.8) .465
Yes 43 (61.4) 22 793 (18 612–27 906) 35.6 (28.3–44.6)
Type of antipyretic
 Only acetaminophen 43 (36.1) 17 132 (13 886–21 136) Reference 26.3 (21.3–32.5) Reference
 Only loxoprofen 35 (29.4) 14 820 (11 167–19 669) .744 25.4 (2.6–31.2) .991
 Only ibuprofen 14 (11.8) 20 306 (13 383–30 811) .815 41.2 (28.5–59.7) .068
 Othera 27 (22.7) 20 613 (15 651–27 149) .637 35.9 (28.3–45.6) .135
Total dosage of antipyretic during 7-days after vaccination
 Acetaminophen, mg, median (IQR) 900 (400–1200) r = 0.072b .648 r = .247b .111
 Loxoprofen, mg, median (IQR) 120 (60–180) r = 0.097b .580 r = .223b .198
 Ibuprofen, mg, median (IQR) 200 (150–400) r = –0.346b .226 r = –.201b .491
Timing of antipyretic use
Antipyretic use on the day of vaccination No 108 (90.8) 17 151 (14 856–19 797) .398 30.0 (26.4–34.1) .308
Yes 11 (9.2) 20 903 (14 378–30 395) 24.3 (16.9–34.9)

Abbreviations: CI, confidence interval; GMT, geometric mean titer; IQR, interquartile range.

a

Including other type of antipyretics, combination drugs, or combination of several antipyretics.

b

r values refer to the Spearman correlation coefficient.

Association Between the Presence or Absence of an Adverse Reaction After the Second Dose and the Emergence of the Same Reaction After the Booster Dose

Using the data of 164 participants for whom information on both the second and booster doses were available, the probability of a solicited adverse reaction after the booster dose was investigated by the presence or absence of the corresponding reaction after the second dose (Table 4). The RR of all solicited adverse reactions was >1.0. The presence of swelling at the injection site, fever of ≥38.0°C, headache, chills, muscle pain, and joint pain after the second dose showed a significant association with the emergence of the corresponding reaction after the booster dose. The RR was the highest for the fever, at 3.97 (95% CI, 2.48–6.35).

Table 4.

Probability of an Adverse Reaction After the Booster Dose According to the Presence or Absence of the Same Reaction After the Second Dose

Adverse Reaction Corresponding Reactions After Booster Dose Incidence of a Corresponding Reaction After Booster Dose, % RR (95% CI)
Present Absent
Local reactions after dose 2
 Pain at injection site Present 154 1 99.4 1.12 (.89–1.41)
Absent 8 1 88.9 Reference
 Redness Present 14 16 46.7 1.56 (.98–2.48)
Absent 40 94 29.9 Reference
 Swelling Present 45 23 66.2 1.93 (1.39–2.66)
Absent 33 63 34.4 Reference
Systemic reactions after dose 2
 Fever ≥38.0°C Present 21 12 63.6 3.97 (2.48–6.35)
Absent 21 110 16.0 Reference
 Fatigue Present 129 14 90.2 1.35 (1.00–1.84)
Absent 14 7 66.7 Reference
 Headache Present 80 19 80.8 1.46 (1.15–1.85)
Absent 36 29 55.4 Reference
 Chills Present 52 18 74.3 2.00 (1.48–2.68)
Absent 35 59 37.2 Reference
 Diarrhea Present 3 17 15.0 1.14 (.37–3.50)
Absent 19 125 13.2 Reference
 Muscle pain Present 85 6 93.4 1.22 (1.06–1.40)
Absent 56 17 76.7 Reference
 Joint pain Present 59 21 73.8 1.77 (1.33–2.35)
Absent 35 49 41.7 Reference

Information on vomiting and lymphadenopathy after the second dose were not collected.

Abbreviations: CI, confidence interval; RR, relative risk.

IgG(S-RBD) Titer by the Presence of Fever After the Second and Booster Doses

The 164 participants were divided into 4 groups by the presence or absence of fever of ≥38.0°C after each dose. The IgG(S-RBD) titers of these 4 groups 1 month after the second dose, 8 months after the second dose, and 1 month after the booster dose are shown in Table 5. The GMTs of IgG(S-RBD) 1 month after the second dose were higher for the groups with fever after the second dose than for those without. Eight months after the second dose, the differences among the groups were subtle, ranging from 537 to 796 AU/mL, without significant differences. The GMTs of IgG(S-RBD) 1 month after the booster dose were higher in the groups with fever after the booster dose, and they were comparable between the groups with and without fever after the second dose. A multivariate analysis incorporating fever after the second dose was additionally done. Fever after the booster dose was extracted as being significantly correlated with the IgG(S-RBD) titers after the booster dose (β = .246 [95% CI, .097–.395]; P = .001), but fever after the second dose was not.

Table 5.

Spike Receptor-Binding Domain Immunoglobulin G Titers by the Presence or Absence of Fever After the Second and Booster Doses

Fever ≥38.0°C After Vaccination (After Dose 2/Dose 3) No. (%) Female Sex, No. (%) Age, y, Median (IQR) 1 Month After Dose 2 8 Months After Dose 2 1 Month After Dose 3
GMT (95% CI), AU/mL P Value GMT (95% CI), AU/mL P Value GMT (95% CI), AU/mL P Value
Absent/Absent 110 (67.1) 83 (75.5) 42.0 (33.0–49.0) 8281 (7305–9386) Reference 537 (474–607) Reference 15 438 (13 665–17 441) Reference
Present/Absent 12 (7.3) 9 (75.0) 33.5 (29.0–39.5) 12 026 (8204–17 628) .169 796 (552–1147) 0.144 14 644 (10 630–20 174) .990
Absent/Present 21 (12.8) 12 (57.1) 41.0 (46.0–51.0) 9172 (6717–12 524) .879 738 (515–1058) 0.125 22 012 (16 555–29 270) .060
Present/Present 21 (12.8) 17 (81.0) 40.0 (28.0–44.0) 12 343 (9562–15 932) .032 627 (481–817) 0.682 22 479 (16 575–30 487) .042

Abbreviations: CI, confidence interval; GMT, geometric mean titer; IQR, interquartile range.

DISCUSSION

A booster dose of an mRNA COVID-19 vaccine induces a higher antibody titer than is produced by the primary 2-dose series [18, 19]. Our previous study showed that the IgG(S-RBD) titers after the second dose of the primary series were relatively low for male participants and the elderly [15], as shown in other studies [20, 21]. In contrast, in the present study of the booster dose for the same cohort, male sex and age showed positive correlations with the fold change in IgG(S-RBD) titers, reaching comparable levels in the IgG(S-RBD) titers by sex and age. Other studies have also shown that the specific IgG titers after the BNT162b2 booster were comparable for sex and age [22, 23]. The mechanism for the difference in the immunogenicity of a BNT162b2 vaccine by sex and age between the second and booster doses is unclear, but the booster vaccination would drive antibody production, especially in the populations with relatively weak responses to the primary series.

The relation between the emergence of vaccine-related adverse reactions and antibody induction by the primary series of mRNA COVID-19 vaccines has been reported. Studies that used scores based on the sum of the presence or a severity scale of solicited adverse reactions showed no significant correlation of adverse reactions with the spike-specific IgG titers [24–26]. On the other hand, when each reaction was separately analyzed, the presence of fever after the second dose was shown to be correlated with high IgG titers [27, 28]. We previously showed that degree of fever after the second dose was correlated with the IgG(S-RBD) titers by a multivariate analysis [15]. In the present study, the degree of fever after the booster dose, which was defined by the highest body temperature after the vaccination, was again shown to have a significant correlation with the IgG(S-RBD) titers. Note that the clinical significance of the difference in the IgG(S-RBD) titers due to postvaccination fever (eg, the GMTs for the participants with fever of <37.0°C and ≥38.0°C were 14 011 AU/mL and 23 020 AU/mL, respectively) for protection against SARS-CoV-2 infection is difficult to evaluate. In general, the IgG(S-RBD) titers measured with the assay used in our study were shown to be correlated with the neutralizing antibody levels, a surrogate marker for protection, although the correlation at relatively high IgG(S-RBD) titers, as detected in our study, has been inconsistent across studies [29–31]. A positive correlation was reported not only for wild-type virus but also for variants including B.1.617.2 (Delta) and B.1.1.529 (Omicron) [32]. The mechanism of how fever after SARS-CoV-2 mRNA vaccination is linked to antibody production remains unclear. Elucidating the mechanism will lead to a better understand of the sufficient antibody induction mechanism of mRNA COVID-19 vaccines.

The possibility of a relation between postvaccination fever and the SARS-CoV-2–specific antibody titers has created concern that antipyretics, which can suppress fever, may have a negative influence on antibody responses to SARS-CoV-2 vaccination. To date, few studies have been done to determine the influence of antipyretics on the immunogenicity of COVID-19 vaccines. We previously showed that the use of antipyretics for fever or other adverse reactions did not interfere with the antibody responses to the primary BNT162b2 series [15]. In the present study for the BNT162b2 booster, no influence of antipyretic use on the IgG(S-RBD) titers was observed again. Although several in vitro laboratory studies have demonstrated that NSAIDs inhibit several pathways leading to antibody responses [33–35], the IgG(S-RBD) titers of the group with NSAIDs were comparable to those of the group with acetaminophen. The present study was not designed to evaluate the influence by the type of antipyretics, but it is suggested that neither acetaminophen nor NSAIDs would interfere with the elevation of IgG(S-RBD) titers. Antipyretics may also be used prophylactically. One study of a COVID-19 adenoviral vector vaccine reported that prophylactic acetaminophen use reduced many adverse reactions without interfering with antibody responses [36]. There are no studies on the influence of prophylactic use of antipyretics on antibody responses to mRNA COVID-19 vaccines. Taken together, our results indicate that the use of antipyretics for emerging adverse events, regardless of the type, acetaminophen or NSAIDs, would be helpful for alleviating adverse reactions, including fever, without interfering with antibody responses to SARS-CoV-2 mRNA vaccination.

It would be of great interest for physicians to determine whether the presence of an adverse reaction after the 2-dose primary series is useful to predict the emergence of the corresponding reaction after the booster dose. In the present study, the presence of swelling as a local reaction and several systemic reactions, including fever after the second dose, was associated with the emergence of the corresponding reactions after the booster dose. Fever after the second dose showed the highest RR of 3.97. Of interest, fever after the booster dose was independently correlated with the IgG(S-RBD) titers after the booster dose, irrespective of fever after the second dose. Thus, participants with fever after the second dose may be more likely to have fever after the booster dose, but fever after the second dose would not affect the antibody responses to the booster dose. To our knowledge, no investigations of the correlation between postvaccination fever and specific IgG levels have been done in the same cohort throughout the primary and booster vaccinations. These findings impress a potential linking of postvaccination fever with the antibody production induced by mRNA COVID-19 vaccines.

This study has some limitations that should be acknowledged. First, it is a single-center observational study with a relatively small sample size of 281 participants. Additionally, the population was relatively young and predominantly female. Second, the data collection methods for the solicited adverse reactions were slightly different between the second and booster doses. The data collection period for adverse reactions was 7 days after vaccination for the booster dose, whereas it was 5 days for the second dose. However, most common adverse reactions have been known to occur within a few days after vaccination [37]; thus, the difference would have little impact on our findings. Finally, the type, dosage, and timing of antipyretic usage were chosen by each participant and are thus arbitrary. Besides, this study has insufficient statistical power due to the relatively small sample size, which may have led to underestimation in the possible negative influence of antipyretic use on the antibody responses. Large-scale randomized controlled studies will be necessary to clarify the influence of antipyretics on the immunogenicity outcomes of COVID-19 vaccines, but we believe that our real-world data from healthcare workers with self-medicated antipyretics is informative.

In conclusion, a booster dose of BNT162b2 vaccine can restore waning immunity and significantly increase the antibody titers, especially in males and the elderly who had relatively low antibody responses to the primary 2-dose series. Post–booster vaccination fever could be independently correlated with mRNA vaccine–induced specific IgG levels, without any significant influence of fever after the primary series. Although the relatively small sample size in this study means that our results are inconclusive, they indicate that antipyretic medications would be helpful to alleviate suffering from adverse reactions, without suppressing the specific IgG responses induced by a BNT162b2 vaccine booster.

Supplementary Material

ofac493_Supplementary_Data

Contributor Information

Naoki Tani, Medicine and Biosystemic Science, Kyushu University Graduate School of Medical Sciences, Fukuoka, Japan.

Hideyuki Ikematsu, Ricerca Clinica Co, Fukuoka, Japan.

Takeyuki Goto, Medicine and Biosystemic Science, Kyushu University Graduate School of Medical Sciences, Fukuoka, Japan.

Kei Gondo, Clinical Laboratory, Fukuoka City Hospital, Fukuoka, Japan.

Takeru Inoue, Medicine and Biosystemic Science, Kyushu University Graduate School of Medical Sciences, Fukuoka, Japan.

Yuki Yanagihara, Pharmacy, Fukuoka City Hospital, Fukuoka, Japan.

Yasuo Kurata, Pharmacy, Fukuoka City Hospital, Fukuoka, Japan.

Ryo Oishi, Department of Infectious Diseases, Fukuoka City Hospital, Fukuoka, Japan.

Junya Minami, Department of Infectious Diseases, Fukuoka City Hospital, Fukuoka, Japan.

Kyoko Onozawa, Department of Infectious Diseases, Fukuoka City Hospital, Fukuoka, Japan.

Sukehisa Nagano, Department of Neurology, Fukuoka City Hospital, Fukuoka, Japan.

Hiroyuki Kuwano, Department of Surgery, Fukuoka City Hospital, Fukuoka, Japan.

Koichi Akashi, Medicine and Biosystemic Science, Kyushu University Graduate School of Medical Sciences, Fukuoka, Japan.

Nobuyuki Shimono, Center for the Study of Global Infection, Kyushu University Hospital, Fukuoka, Japan.

Yong Chong, Medicine and Biosystemic Science, Kyushu University Graduate School of Medical Sciences, Fukuoka, Japan.

Supplementary Data

Supplementary materials are available at Open Forum Infectious Diseases online. Consisting of data provided by the authors to benefit the reader, the posted materials are not copyedited and are the sole responsibility of the authors, so questions or comments should be addressed to the corresponding author.

Notes

Acknowledgments. We thank all of the staff members of Fukuoka City Hospital for their support for sample collection and data reduction.

Financial support. This work was supported by our own resources.

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Supplementary Materials

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