SARS-CoV-2: comparison of IgG levels at 9 months post second dose of vaccination in COVID-survivor and COVID-naïve healthcare workers

Shagun B. Shah, Rajiv Chawla, Sudhir K. Rawal, Anurag Mehta, Anuj Parkash


Background: Natural (asymptomatic/symptomatic COVID-19 infection) and artificial (vaccination) exposure to the pathogen represent two modes of acquiring active immunity. No definitive guidelines exist regarding whether COVID-survivors (with infection/re-infection/re-re-infection in the three COVID-19 waves) require a modified vaccination schedule. Most countries are offering a third vaccine dose and many are contemplating a fourth dose. Our aim was to gauge the IgG-antibody levels 9m post second vaccination in healthcare workers (HCW) and compare these with IgG-levels 1m post-vaccination in the same cohort for any decline, and to compare the post-vaccination IgG-levels in COVID-survivors and COVID-naïve HCW at 9m.

Methods: This prospective observational single-centric cohort study included 63 HCW of either sex, aged 18-70y who completed 9m post-vaccination. The IgG-titre was tested at 9-10m post second vaccination in COVID-survivors and COVID-naïve HCW.

Results: At 1m and 9m post-vaccination IgG-levels in COVID-survivors (23.097±4.58 and 15.103±4.367 respectively; p<0.0001) and COVID-naïve HCW (16.277±6.36 and 9.793±6.928 respectively; p=0.0013) had unequal variance (Welsch test; p=0.0022 at 9m). 9/31 COVID-naïve HCW but none of the 32 COVID-survivors tested COVID-positive in the second wave post second vaccination. 11/31 and 3/32 HCW belonging to the former and latter groups developed COVID-19 in the third wave consequently deferring their third/precautionary vaccination.

Conclusions: Although HCW with IgG-levels in all brackets developed COVID-19, the severity of symptoms corresponded with the IgG-levels. COVID-19 is here to stay, but in peaceful co-existence in endemic proportions. Considering evidence that immunity acquired by vaccination/natural infection is ephemeral, re-invention of vaccines to match the ever-mutating virus is foreseen.  


COVID-19, Immunity, Vaccine

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COVID-19 Vaccine Third Dose Recommendations. Available at: ams/publichealth/coronavirus/docs/vaccine/COVID-19_vaccine_third_dose_recommendations.pdf. Accessed on 15 March 2022.

FDA Authorizes Booster Dose of Pfizer-BioNTech COVID-19 Vaccine for Certain Populations. Available at: Accessed on 14 March 2022.

Precaution dose and children vaccination. Available at: Accessed on 15 March 2022.

Countries weigh need for COVID-19 booster shots. Available at: thcare-pharmaceuticals/countries-weigh-need-covid-19-booster-shots-2022-01-18/ Accessed on 15 March 2022

Shah SB, Chawla R, Mehta A, Bansal N, Jain CR, Prakash A et al. SARS-CoV-2: Comparison of Active Immunity Acquired by Natural Exposure versus Inoculation of HCW. Gal Int J Health Sci Res. 2021;6:54-63.

Singh AK, Phatak SR, Singh R, Bhattacharjee K, Singh NK, Gupta A, Sharma A. Antibody response after first and second-dose of ChAdOx1-nCOV (CovishieldTM®) and BBV-152 (CovaxinTM®) among health care workers in India: the final results of cross-sectional coronavirus vaccine-induced antibody titre (COVAT) study. Vaccine. 2021;39(44):6492-509.

Thiagarajan K. What do we know about India’s Covaxin vaccine?. BMJ: British Medical Journal (Online). 2021;373.

Jones I, Roy P. Sputnik V COVID-19 vaccine candidate appears safe and effective. Lancet. 2021;397:642-3

Voysey M, Clemens SA, Madhi SA, Weckx LY, Folegatti PM, Aley PK et al. Safety and efficacy of the ChAdOx1 nCoV-19 vaccine (AZD1222) against SARS-CoV-2: an interim analysis of four randomised controlled trials in Brazil, South Africa, and the UK. The Lancet. 2021;397(10269):99-111.

Instructions for use CoV2G. Available at: Instructions for use CoV2G VITROS Immunodiagnostic Products Anti-SARS-CoV-2 IgG Reagent Pack 619 9919 - Bing. Accessed on 15 March 2022.

Lahariya C. Third wave of the COVID-19 pandemic in India: What lies ahead? Available at: Accessed on 15 March 2022.

Thiagarajan K. COVID-19: India is at centre of global vaccine manufacturing, but opacity threatens public trust. BMJ. 2021;372:196-8.

Das S, Kar SS, Samanta S, Banerjee J, Giri B, Dash SK. Immunogenic and reactogenic efficacy of Covaxin and Covishield: a comparative review. Immunol Res. 2022;22:1-27.

Covid vaccine: India starts jabs for 12- to 14-year-olds. Available at: -asia-india56345591#:~:text=The%20country%2 0has%20administered%20over,been%20partially%20vaccinated%. Accessed on 15 March 2022.

Bubar KM, Reinholt K, Kissler SM, Lipsitch M, Cobey S, Grad YH et al. Model-informed COVID-19 vaccine prioritization strategies by age and serostatus. Science. 2021;9:10-8.

COVID vaccine makers brace for a variant worse than Delta. Available at: articles/d41586-021-02854-3. Accessed on 15 March 2022.