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. 2020 Nov 4;39(6):886–888. doi: 10.1016/j.vaccine.2020.10.094

Duration of anti-SARS-CoV-2 antibodies much shorter in India

Nishant Kumar a, Shibal Bhartiya b, Tarundeep Singh c,
PMCID: PMC7641879  PMID: 33189428

Abstract

Seroprevalence survey, for antibodies to SARS-CoV-2, of healthcare workers (HCW) working in three Government run hospitals in Mumbai was carried out in June 2020. Among the 801 HCWs tested, seroprevalence was 11.1%. Males (13.5% vs. 8.9% in females) and ancillary workers (18.5% vs 6.9% in doctors and nurses) were more likely to be seropositive. Sixty-two (7.74%) had been previously diagnosed with RT PCR test for SARS-CoV-2. Of these, 44 (71%) were seronegative. Upto 28 days after a positive PCR test, 90% of subjects were found to be seropositive. This reduced to less than half (38.5%) between 29 and 42 days. None of 28 infected HCWs who had the RT-PCR more than 50 days ago tested positive for antibodies. It seems likely that cellular immunity plays a larger role in defence against the illness.


Humoral immune response to SARS-CoV-2 infection have been reported to be variable, but short-lived [1], [2], [3], [4]. We carried out a seroprevalence survey of healthcare workers (HCW) working in three Government run hospitals in Mumbai. Pan immunoglobulin Elecsys Anti-SARS-CoV-2 Assay (Roche Diagnostics, Rotkreuz, Switzerland) using recombinant protein representing the nucleocapsid (N) antigen in double antigen sandwich assay format was done after informed consent. This test has a specificity of 99.8% and 100% sensitivity for patients, fourteen days post-PCR confirmation. The result is given as a cut off index (CoI), and is then interpreted either as reactive/positive (CoI ≥ 1.0) or non-reactive/negative (CoI < 1.0) [5]. We did not test for the antibodies against S antigen. A pretested, validated questionnaire in local language was used to collect data on demographic details and symptoms.

The study was approved by Institutional Ethics Committee of the JJ group and Grant Medical College, Mumbai, India.

Among the 801 HCWs who got tested, seroprevalence was 11.1%. Males (13.5% vs. 8.9% in females) and ancillary workers (18.5% vs 6.9% in doctors and nurses) were more likely to be seropositive (Table 1 ).

Table 1.

Seroprevalence as per different demographic and comorbidity characteristics.

Group All Sero (−) Sero (+) % (+) 95% CI p value Odds ratio
All 801 712 89 11.1 9.1–13.5



Occupation
Ancillary workers 292 238 54 18.5 14.5–23.3 Odds = 0.227
Doctors 201 187 14 7.0 4.2–11.4 OR = 2.65
Nurses 308 287 21 6.8 4.5–10.2 OR = 2.71



Gender
Male 386 334 52 13.5 10.4–17.3 p = 0.04 OR = 1.51
Female 415 378 37 8.9 6.5–12.1



Age group
20–40 years 413 372 41 9.9 7.4–13.2 p = 0.54 OR = 0.803
40–60 years 380 333 47 12.4 9.4–16.1
>=60 years 8 7 1 12.5 2.2–47.1



Comorbidities
None 682 604 78 11.4 9.3–14.1 0.49
Single 103 94 9 8.7 4.5–16.0 0.62
Multiple 16 14 2 12.5 2.2–37.3
Cancer 5 4 1 20.0 2.0–64.0 0.94
Immunosuppression 11 9 2 18.2 4.0–48.9 0.45
Asthma 35 32 3 8.6 2.2–23.1 0.67
Cardiac problems 48 44 4 8.3 2.8–20.1 0.56
Diabetes mellitus 38 35 3 7.9 2.0–21.5 0.56

There was significantly higher seroprevalence in those previously diagnosed with COVID-19 with a positive PCR test compared to those who had not been tested by RT-PCR; 29% (CI 19.2–41.4) compared to 9.6% (CI 7.7–12). Sixty-two (7.74%) had been previously diagnosed with RT PCR test for SARS-CoV-2. Of these, 44 (71%) were seronegative. Individuals who were symptomatic in the last 30 days with any of the symptoms associated with COVID-19 had a significantly higher seropositive rate; 16.8% (CI 11.8–23.2) compared to 9.6% (CI 7.6–12.2). Sub-analysis of the various symptoms indicates that only loss of smell or taste and presence of non-specific febrile illness in the last 30 days were significant variables associated with higher seroprevalence. None of the other symptoms associated with COVID-19 were statistically significant (Table 2 ).

Table 2.

Seroprevalence and associated factors.

Group All Sero (−) Sero (+) +ve (%) 95% CI p value
PCR positive individuals
COVID PCR (+) 62 44 18 29.0 19.2–41.4 0.000003
OR = 3.02
COVID PCR (−) 739 668 71 9.6 7.7–12.0
Symptomatic in last month 167 139 28 16.8 11.8–23.2 0.0001
OR = 2.655
Asymptomatic in last month 634 573 61 9.6 7.6–12.2



Symptoms associated with seropositivity
Loss of taste/smell 10 4 6 60.0 31.2–83.3 0.0003
OR = 2.71
No loss of taste/smell 791 708 83 10.5 8.5–12.8
Acute Febrile Illness 28 15 13 46.4 29.5–64.2 0.000002
OR = 1.51
No acute Febrile Illness 773 697 76 9.8 7.9–12.1
Any Acute Respiratory Illness 97 83 14 14.4 8.7–22.9 0.26
No acute Respiratory Illness 704 629 75 10.7 8.6–13.2
Acute Respiratory Illness – SARI 16 13 3 18.8 5.8–43.8 0.59
Acute Respiratory Illness – ILI 81 70 11 13.6 7.6–22.9
Non-specific illness 90 78 12 13.3 7.6–22.0 0.47
No Non-specific illness 711 634 77 10.8 8.7–13.3
Acute Gastric/enteric illness 8 7 1 12.5 0.1–49.2 0.83
No acute gastric/enteric illness 793 705 88 11.1 9.1–13.5
Eye Redness 12 11 1 8.3 0.0–37.5 0.84
No Eye Redness 789 701 88 11.2 9.1–13.6
Skin rash 9 8 1 11.1 0.0–45.7 0.91
No skin rash 792 88 704 88.9 86.5–90.9

Subjects who had visited a fever clinic in the last 30 days had a significantly higher seroprevalence; 20.5% (CI 14.4–28.2) compared to 9.3% (CI 7.3–11.7). Individuals with a family member living in the same house diagnosed with COVID-19 had a significantly higher seroprevalence; 18.9% (CI 11.5–29.4) compared to 10.3% (CI 8.3–12.8). Having a COVID-19 patient living within 50 m of the individual’s residence was not a significant factor for increased seroprevalence (see Table 3 ).

Table 3.

Seroprevalence based on exposure.

Group All Sero (−) Sero (+) (+) % 95% CI p value Odds ratio
Risk/exposure characteristics
Visited Fever clinic 132 105 27 20.5 14.4–28.2 0.0002 OR = 2.52
Not visited fever clinic 669 607 62 9.3 7.3–11.7
Household person positive 74 60 14 18.9 11.5–29.4 0.02 OR = 2.03
No household person positive 727 652 75 10.3 8.3–12.8
Neighbourhood person positive 397 348 49 12.3 9.4–16.0 0.27
No Neighbourhood person positive 404 364 40 9.9 7.3–13.2

Duration between positive RT-PCR test and serological testing ranged from 15 to 49 days for 34 (54.8%), and >50 days in 28 subjects. Upto 28 days after a positive PCR test, 90% of subjects were found to be seropositive. This reduced to less than half over next two weeks (38.5%) between 29 and 42 days. This further reduced to less than 15% for subjects who were tested between 43 and 49 days of their positive RT-PCR. None of the 28 infected HCWs who had had the RT-PCR more than 50 days ago tested positive for the antibodies. Of the people who had never been RT PCR positive, 9.6% had antibodies (Table 4 ). The mean antibody levels of people who had never been tested for RT PCR were 26.77 CoI (28.47 CoI in those with RT PCR test positive).

Table 4.

Weekwise anti SARS-CoV-2 antibody levels in Healthcare workers in Mumbai, India.

Days after (+)ve RT-PCR Test No. Of persons Positives# Antibody levels mean (std dev) COI Outliers* n (values)
15–21 5 3 1.01 (1.61) 1 (14.26)
22–28 11 9 31.7 (31.3) 1 (0.08)
29–35 7 2 0.93 (1.81) 1 (73)
36–42 6 1 0.1 (0.1) 1 (12.91)
43–49 6 1 0.1 (0.03) 1 (28.93)
50–56 9 0 0.07 (0.01) 0
>56 18 0 0.08 (0.01) 2 (0.92, 0.12)
#

COI > 1 is considered positive.

*

Outliers have not been included in the calculation of mean and std. dev.

Our findings are in agreement with the view that humoral response is launched rapidly and peaks at about 3–4 weeks with an exponential decline thereafter [1], [2], [3], [4]. This however is in contrast to the findings of Gudbjartsson et al in Iceland where more than 90% of persons with previously positive RT PCR tests had neutralizing antibodies after 4 months [4]. Nearly 9.6% of HCWs have been asymptomatic and never tested with RT PCR but had anti SARS-CoV-2 antibodies indicating asymptomatic infections. Antibody levels in such asymptomatics are similar to levels seen in symptomatics which is contrary to findings by Long et al. [2]. Susceptibility of subjects to re-infection after antibody response has subsided is a matter of investigation, but has shown to be unlikely in rhesus experimental models [6]. Since the reported rates of re-infection are quite low, it is possible that cellular immunity or antibodies to the S antigen may play a greater role in defence against COVID 19.

Key findings

  • (1)

    Humoral antibody response to SARS-CoV-2 is much shorter in Indian population as compared to previously reported.

  • (2)

    Cellular immunity or other antibodies may play a larger role in providing protection against the disease.

  • (3)

    These facts need to be kept in mind before planning vaccine studies.

Funding

There was no funding for the study.

Data is available from the authors upon request.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

References

  • 1.Wang X., Guo X., Xin Q., Pan Y., Hu Y., Li J., et al. Neutralizing antibodies responses to SARS-CoV-2 in COVID-19 inpatients and convalescent patients. Clin Infect Dis. 2020;721 doi: 10.1093/cid/ciaa721. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 2.Long Q.-X., Tang X.-J., Shi Q.-L., Li Q., Deng H.-J., Yuan J., et al. Clinical and immunological assessment of asymptomatic SARS-CoV-2 infections. Nat Med. 2020;26(8):1200–1204. doi: 10.1038/s41591-020-0965-6. [DOI] [PubMed] [Google Scholar]
  • 3.Suthar M.S., Zimmerman M., Kauffman R., Linderman S.L., Hudson W.H., Vanderheiden A., et al. Rapid generation of neutralizing antibody responses in COVID-19 patients. Cell Rep Med. 2020;1(3) doi: 10.1016/j.xcrm.2020.100040. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 4.Gudbjartsson DF, Norddahl GL, Melsted P, Gunnarsdottir K, Holm, et al. Humoral Immune Response to SARS-CoV-2 in Iceland. N Engl J Med 2020 available at www.nejm.org/doi/10.1056/NEJMoa2026116 [accessed on 5 September 2020]. [DOI] [PMC free article] [PubMed]
  • 5.Kontou P.I., Braliou G.G., Dimou N.L., Nikolopoulos G., Bagos P.G. Antibody tests in detecting SARS-CoV-2 infection: a meta-analysis. Diagnostics (Basel). 2020;10(5):319. doi: 10.3390/diagnostics10050319. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 6.Bao, L., et al. Reinfection could not occur in SARS-CoV-2 infected rhesus macaques. Preprint at bioRxiv; 2020 https://doi.org/10.1101/2020.03.13.990226.

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