Non-COVID Health Care Workers with Positive Antibody Responses: Are We Heading Towards Herd Immunity?

Sudhir Bhandari, Nitya Vyas, Shivankan Kakkar, Bhoopendra Patel, Amitabh Dube, Jitendra Gupta, Natwar K. Swarnkar, Sunil Kumar, Nisha Patidar


Background: Antibody testing against SARS-CoV-2 complimentary to RT-PCR could be an effective method for its detection. Development of immunity against COVID-19 in context of reinfection and herd immunity still remains debatable and needs further elucidation. The present study was conducted to investigate the immunity status against SARS-CoV-2 in terms of IgG antibody positivity in health care workers at a tertiary care center. Methodology: This single center study was conducted at a tertiary care center, that involved 1039 healthcare workers and other staff members. The testing of all subjects was performed using ELIFAST (SARS-CoV-2 IgG ELISA) kits. The sample population was then segregated into RT-PCR positive and negative/status unknown groups. Groups were further segregated on the basis of IgG positivity status and the sensitivity and specificity was also calculated. Results: Among the 1039 enrolled subjects, 179 (17.23%) were RT-PCR positive for SARS-CoV-2 positive and remaining were either RT-PCR negative or status unknown cases. Among 179 COVID-19 recovered subjects, 19 (10.61%) were negative for IgG, whereas 160 (89.39%) came out IgG positive. Out of 860 (82.77%) RT-PCR Negative/Status unknown, 248 (28.84%) came out IgG positive and the remaining 612 (71.16%) were negative for IgG. The overall sensitivity and specificity were 89.39 and 71.16, respectively. Conclusion: A combined approach of testing for COVID-19 using RT-PCR and rapid antibody assays could be more beneficial. Serological studies project a higher antibody response in population that compel us to think about plausibility of herd immunity. However, variability in serological response could be affected by several factors and the underlying complex immune process of COVID-19 is yet to be fully understood.


Antibodies, Corona Virus Disease-19 (COVID-19), Herd immunity and Serological

Full Text:



Wang C, Horby PW, Hayden FG, Gao GF. A novel coronavirus outbreak of global health concern. Lancet. 2020; 395(10223): 470-473.

World Health Organization (WHO). Coronavirus disease (COVID-19) pandemic. Available from: [Accessed on 12 February 2021].

Ali Jadoo SA. The second wave of COVID-19 is knocking at the doors: have we learned the lesson?. jidhealth [Internet]. 8Oct.2020 [cited 19Apr.2021];3(Special1):183-4. Available from:

Lazar AM. Understanding SARS-CoV-2 features of infectivity, aggressiveness, and transmissibility: an insect-vector theory for SARS-CoV-2 dissemination. jidhealth [Internet]. 15Apr.2021 [cited 19Apr.2021];4(Special1):343-7. Available from:

Ward S, Lindsley A, Courter J, Assa'ad A. Clinical testing for COVID-19. J Allergy Clin Immunol. 2020;146(1):23-34.

Gupta N, Bhatnagar T, Rade K, Murhekar M, Gangakhedkar RR, Nagar A et al. Strategic planning to augment the testing capacity for COVID-19 in India. Indian J Med Res. 2020;151(2 & 3):210-215.

Long QX, Liu BZ, Deng HJ, Wu GC, Deng K, Chen YK et al. Antibody responses to SARS-CoV-2 in patients with COVID-19. Nat Med. 2020;26:845–848.

Cheng MP, Papenburg J, Desjardins M, Kanjilal S, Quach C, Libman M et al. Diagnostic Testing for Severe Acute Respiratory Syndrome-Related Coronavirus 2: A Narrative Review. Ann Intern Med. 2020;172(11):726-734.

Theel ES, Slev P, Wheeler S, Couturier MR, Wong SJ, Kadkhoda K. The role of antibody testing for SARS-CoV-2: is there one? J Clin Microbiol. 2020;58:e00797-20.

Li Z, Yi Y, Luo X, Xiong N, Liu Y, Li S et al. Development and clinical application of a rapid IgM-IgG combined antibody test for SARS-CoV-2 infection diagnosis. J Med Virol. 2020;92(9):1518-1524.

Xiao AT, Tong YX, Zhang S. False negative of RT-PCR and prolonged nucleic acid conversion in COVID-19: Rather than recurrence. J Med Virol. 2020;92(10):1755-1756.

Long C, Xu H, Shen Q, Zhang X, Fan B, Wang C et al. Diagnosis of the Coronavirus disease (COVID-19): rRT-PCR or CT? Eur J Radiol. 2020;126:108961.

Lassaunière R, Frische A, Harboe ZB, Nielsen ACY, Fomsgaard A, Krogfelt KA et al. Evaluation of nine commercial SARS-CoV-2 immunoassays. medRxiv (Preprint) 2020.04.09.20056325.

Montesinos I, Gruson D, Kabamba B, Dahma H, Van den Wijngaert S, Reza S et al. Evaluation of two automated and three rapid lateral flow immunoassays for the detection of anti-SARS-CoV-2 antibodies. J Clin Virol. 2020;128:104413.

Tré-Hardy M, Wilmet A, Beukinga I, Dogné JM, Douxfils J, Blairon L. Validation of a chemiluminescent assay for specific SARS-CoV-2 antibody. Clin Chem Lab Med. 2020;58(8):1357-1364.

Spicuzza L, Montineri A, Manuele R, Crimi C, Pistorio MP, Campisi R et al. Reliability and usefulness of a rapid IgM-IgG antibody test for the diagnosis of SARS-CoV-2 infection: A preliminary report. J Infect. 2020;81(2):e53-e54.

Cassaniti I, Novazzi F, Giardina F, Salinaro F, Sachs M, Perlini S et al. Performance of VivaDiag COVID-19 IgM/IgG Rapid Test is inadequate for diagnosis of COVID-19 in acute patients referring to emergency room department. J Med Virol. 2020;92(10):1724-1727.

Döhla M, Boesecke C, Schulte B, Diegmann C, Sib E, Richter E et al. Rapid point-of-care testing for SARS-CoV-2 in a community screening setting shows low sensitivity. Public Health. 2020; 182:170-172.

Shen B, Zheng Y, Zhang X, Zhang W, Wang D, Jin J et al. Clinical evaluation of a rapid colloidal gold immunochromatography assay for SARS-Cov-2 IgM/IgG. Am J Transl Res. 2020;12(4):1348–1354.

World Health Organization (WHO). Interim Guidance. 2020. Antigen-detection in the diagnosis of SARS-CoV-2 infection using rapid immunoassays. 11 September 2020. Available from: [Accessed on 12 February 2021].

Mak GC, Cheng PK, Lau SS, Wong KK, Lau CS, Lam ET et al. Evaluation of rapid antigen test for detection of SARS-CoV-2 virus. J Clin Virol. 2020; 129:104500.

Indian Council of Medical Research (ICMR), Department of Health Research: Advisory to start rapid antibody based blood test for COVID-19 (04 April 2020). Available from: [Accessed on 15/02/2021].

Wang P. Combination of serological total antibody and RT-PCR test for detection of SARS-COV-2 infections. J Virol Methods. 2020; 283:113919.

Naaber P, Hunt K, Pesukova J, Haljasmägi L, Rumm P, Peterson P et al. Evaluation of SARS-CoV-2 IgG antibody response in PCR positive patients: Comparison of nine tests in relation to clinical data. PLoS One. 2020;15(10):e0237548.

Wang J, Chen C, Li Q, Cai P, Wang Z, Wang L. COVID-19 confirmed patients with negative antibodies results. BMC Infect Dis. 2020; 20:698.

Cancella de Abreu M, Choquet C, Petit H, Bouzid D, Damond F, Marot S et al. SARS-CoV-2 IGM and IGG rapid serologic test for the diagnosis of COVID-19 in the emergency department. J Infect. 2020;81(5):816-846.

Zhao J, Yuan Q, Wang H, Liu W, Liao X, Su Y et al. Antibody responses to SARS-CoV-2 in patients of novel coronavirus disease. Clin Infect Dis. 2020;71(16):2027-2034.

Kellam P, Barclay W. The dynamics of humoral immune responses following SARS-CoV-2 infection and the potential for reinfection. J Gen Virol. 2020;101(8):791-797.

Cervia C, Nilsson J, Zurbuchen Y, Valaperti A, Schreiner J, Wolfensberger A et al. Systemic and mucosal antibody responses specific to SARS-CoV-2 during mild versus severe COVID-19. J Allergy Clin Immunol. 2021;147(2):545-557.e9.

Liu Y, Yan LM, Wan L, Xiang TX, Le A, Liu JM et al. Viral dynamics in mild and severe cases of COVID-19. Lancet Infect. Dis. 2020;20(6):656-657.

Zhou F, Yu T, Du R, Fan G, Liu Y, Liu Z et al. Clinical course and risk factors for mortality of adult inpatients with COVID-19 in Wuhan, China: a retrospective cohort study. Lancet. 2020;395(10229):1054-1062.

Hindustan Times. 1 in 5 adults exposed to Covid-19: Key points of ICMR’s nationwide sero survey. Available from: [Accessed on 19 February 2021].

Topley WWC, Wilson GS. The spread of bacterial infection: The problem of herd immunity. J Hyg (Lond). 1923; 21(3): 243–249.

Anderson RM, Vegvari C, Truscott J, Collyer BS. Challenges in creating herd immunity to SARS-CoV-2 infection by mass vaccination. Lancet. 2020;396(10263):1614-1616.

Aschwanden C. (21 October 2020). The false promise of herd immunity for COVID-19. Nature, NEWS FEATURE. Available from: [Accessed on 19 February 2021].



  • There are currently no refbacks.

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 International License.

2013-2023 (CC-BY) Australian International Academic Centre PTY.LTD.

Advances in Bioscience and Clinical Medicine