Table 4.
Estimated Vaccine Effectiveness of a Messenger RNA (mRNA) Booster Dose Against Coronavirus Disease 2019 Among US Healthcare Personnel Who Received 2 mRNA Doses, by Subgroup, October 2021–June 2022
| Characteristic by Variant Period | Booster Dose Recipients/All Participants in Group (%)a | Adjusted VE (95% CI)b | |
|---|---|---|---|
| Case-Participants | Control-Participants | ||
| Overall period | |||
| Age, y | |||
| <50 | 1407/2472 (56.9) | 2356/2938 (80.2) | 70.4 (65.4–74.6) |
| ≥50 | 447/718 (62.3) | 797/954 (83.5) | 73.8 (65.6–80.1) |
| Underlying health conditions | |||
| No | 599/929 (64.5) | 941/1132 (83.1) | 67.6 (58.7–74.6) |
| Yes | 1255/2261 (55.5) | 2212/2760 (80.1) | 72.3 (67.5–76.3) |
| Pregnancyc | |||
| No | 1096/1947 (56.3) | 1864/2328 (80.1) | 74.7 (70.2–78.6) |
| Yes | 37/69 (53.6) | 70/89 (78.7) | 74.2 (46.5–87.6) |
| Immunocompromisedd | |||
| No | 1820/3132 (58.1) | 3076/3804 (80.9) | 75.1 (71.5–78.2) |
| Yes | 34/58 (58.6) | 77/88 (87.5) | 85.0 (64.8–93.6) |
| Delta periode | |||
| Age, y | |||
| <50 | 76/485 (15.7) | 309/608 (50.8) | 85.3 (78.8–89.7) |
| ≥50 | 20/128 (15.6) | 113/207 (54.6) | 89.2 (80.0–94.2) |
| Underlying health conditions | |||
| No | 39/189 (20.6) | 125/230 (54.3) | 82.8 (71.2–89.7) |
| Yes | 57/424 (13.4) | 297/585 (50.8) | 87.8 (82.1–91.7) |
| Pregnancyc | |||
| No | 58/374 (15.5) | 232/465 (49.9) | 85.9 (79.0–90.6) |
| Yes | 2/14 (14.3) | 14/26 (53.8) | 86.7 (23.3–97.7) |
| Immunocompromisedd | |||
| No | 95/599 (15.9) | 416/803 (51.8) | 85.4 (80.3–89.2) |
| Yes | 1/14 (7.1) | 6/12 (50.0) | 93.3 (25.0–99.4) |
| Omicron periode | |||
| Age, y | |||
| <50 | 1331/1987 (67.0) | 2047/2330 (87.9) | 64.0 (57.1–69.9) |
| ≥50 | 427/590 (72.4) | 684/747 (91.6) | 66.9 (53.1–76.7) |
| Underlying health conditions | |||
| No | 560/740 (75.7) | 816/902 (90.5) | 55.5 (39.4–67.3) |
| Yes | 1198/1837 (65.2) | 1915/2175 (88.0) | 67.2 (60.6–72.7) |
| Pregnancyc | |||
| No | 1038/1573 (66.0) | 1632/1863 (87.6) | 70.9 (65.0–75.8) |
| Yes | 35/55 (63.6) | 56/63 (88.9) | 74.3 (31.6–90.3) |
| Immunocompromisedd | |||
| No | 1725/2533 (68.1) | 2660/3001 (88.6) | 71.6 (67.0–75.6) |
| Yes | 33/44 (75.0) | 71/76 (93.4) | 74.7 (20.1–92.0) |
Abbreviations: CI, confidence interval; VE, vaccine effectiveness.
Case-participants had symptomatic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection confirmed by antigen or nucleic acid amplification test (NAAT); control-participants had a negative SARS-CoV-2 NAAT result, with or without symptoms. Vaccination status was assigned on the test date as after a booster dose if ≥14 days after a messenger RNA (mRNA) booster dose administered ≥5 months after dose 2; the referent group for analysis was participants with dose 2 receipt ≥5 months before the test date without a booster dose.
VE was estimated as 100% multiplied by 1 minus the odds ratio for vaccination status by case/control status. To account for matching, for estimates by age group and underlying health conditions we used a conditional model with clustering by 2-week matching period and enrolling site; to account for sparse data in estimates by pregnancy status and immunocompromised status, broader clusters were used comprising 4-week periods and the US census region of the enrolling site. Adjusted VE included age group in years (18–29, 30–39, 40–49, or ≥50 years), race and ethnicity (white non-Hispanic or other), educational level (doctoral/professional degree or other), underlying health conditions (yes or no), and known contact with a person with coronavirus disease 2019 outside the workplace (yes or no).
Pregnancy was defined as pregnant on the test date. Analyses by pregnancy status were restricted to female participants aged <50 years.
Immunocompromised status was determined based on self-reported diagnoses or medical record review. During the Omicron-predominant period, the VE of a third dose administered >28 days (instead of >150 days) after dose 2 was 80.2% (39.4%–93.5%) among immunocompromised participants, compared with 71.5% (67.2%–75.2%) among other participants. P values for interactions between subgroups were all >.05.
The Delta-predominant period was defined as before 19 December 2021; the Omicron-predominant period, as 19 December 2021 or later.