International Journal of Research in Medical Sciences | May 2022 | Vol 10 | Issue 5 Page 1139 International Journal of Research in Medical Sciences Shah SB et al. Int J Res Med Sci. 2022 May;10(5):1139-1144 www.msjonline.org pISSN 2320-6071 | eISSN 2320-6012 Original Research Article 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 1 *, Rajiv Chawla 1 , Sudhir K. Rawal 2 , Anurag Mehta 3 , Anuj Parkash 3 INTRODUCTION The two methods of acquiring active immunity against COVID-19 infection are natural exposure to the pathogen or by vaccination. There exist no guidelines as to whether individuals who have previously been documented as COVID-19 positive by the RT-PCR test would require a modified vaccination schedule. Plasma B-cells rapidly divide when exposed to a second dose of the same virus/vaccine. The process of B-cell maturation is also activated by the booster dose resulting in better targeted antibodies. Hence, a second dose produces antibodies faster than the initial exposure/inoculation (which is known to produce an IgG antibody response only after 1 month of exposure). Currently, most countries including India have incorporated a third dose of vaccine for vulnerable 1 Department of Anaesthesia, 2 Department of Surgical Oncology, 3 Department of Laboratory and Transfusion Medicine, Rajiv Gandhi Cancer Institute and Research Centre, Rohini, Delhi, India Received: 23 March 2022 Accepted: 11 April 2022 *Correspondence: Dr. Shagun B. Shah, E-mail: drshagun_2010@rediffmail.com Copyright: © the author(s), publisher and licensee Medip Academy. This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. ABSTRACT 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. Keywords: COVID-19, Immunity, Vaccine DOI: https://dx.doi.org/10.18203/2320-6012.ijrms20221189