key: cord-0920866-ixjo8dwu authors: Sapkal, Gajanan; Srivastava, Rajni Kant; Dwivedi, Gaurav; Sahay, Rima R; Yadav, Pragya D; Deshpande, Gururaj R; Singh, Rajeev; Nyayanit, Dimpal A; Patil, Deepak Y; Shete-Aich, Anita M; Zaman, Kamran; Chaudhari, Anil K; Gupta, Nivedita; Panda, Samiran; Abraham, Priya; Bhargava, Balram title: Immune responses against different variants of SARS-CoV-2 including omicron following six months of administration of heterologous prime-boost COVID-19 vaccine date: 2022-03-04 journal: J Travel Med DOI: 10.1093/jtm/taac033 sha: 0aba5d9938f2d5cfabe39f380809ded5c9397840 doc_id: 920866 cord_uid: ixjo8dwu Comparative analysis at one- and six-months post-vaccination showed modest reduction in S1-RBD IgG antibody and NAb titers against B.1, Alpha, Beta and Delta variants in heterologous and homologous vaccine recipients groups. However, significant reduction in NAb titers against Omicron in vaccinees’ sera post-six months underlines need for cautious prospective follow-up. concern (VOC) Omicron with its high transmissibility, has led to rapid surge in the number of COVID-19 cases including the breakthroughs and re-infections. 1 cohorts, receiving either two doses of homologous Covishield or Covaxin. 4 Out of the eighteen individuals in the heterologous group reported earlier, 4 we could follow-up 17 individuals in the second round at 6 months following administration of the second dose. Here, we report the findings of the IgG antibody responses against S1-RBD and the neutralizing antibody (NAb) titres of the heterologous and homologous vaccination regimes against the SARS-CoV-2 VOCs (Alpha, Beta, Delta) and its comparison with prototype B.1 at 1 and 6 months and with Omicron post-six months. Venous blood (5 ml) was collected in serum separator gel tube vacutainers from each of the participants at 6 months after the second dose. The samples were tested for anti-SARS-CoV-2 IgG antibodies against S1-RBD ELISA as described earlier. 5 Further, the plaque reduction neutralization test ( A significant reduction was observed in the S1-RBD IgG antibody titers in all the three groups i.e., CS/CV group (4.13-fold; p-value <0.0001), CS/CS group (6.80; p-value <0.0001)) and CV/CV group (4.87-fold; p-value <0.0001)) ( Figure-1 B) . The groups were compared using the Wilcoxon matched-pairs signed rank test to assess the statistical significance. Even with the waning antibody response at 6 months, the heterologous group had shown better immune response compared to the homologous groups administered with either Covishield or Covaxin. The comparison of the S1-RBD GMT ratios for heterologous group (1 month/6 month) to the S1-RBD GMT ratios for homologous Keeping in view the ongoing third wave of the pandemic with the emergence of Omicron, the National Technical Advisory Group on Immunization (NTAGI), Government of India has recommended the precautionary doses for those individuals who have completed 9 months after the second dose of Covishield or Covaxin. 9 Immunization with the additional dose has been initiated for all the health care and front-line workers as well as for the elderly above 60 years (with comorbidities) from 10 th January 2022. The gradual shift of VOCs from Delta to Delta-sub-lineage to Omicron along with the observed waning of immunity post-six months of vaccination, has prompted discourses around devising innovative vaccination strategy. The present investigation findings contribute meaningfully to such discussions. Regardless of the findings of this study, longitudinal monitoring for breakthrough severe disease should remain a part of any surveillance system. The study was approved by the Institutional Ethics Committee of the ICMR-Regional Omicron largely evades immunity from past infection or two vaccine doses Immunogenicity and safety of a heterologous prime-boost COVID-19 vaccine schedule: ChAdOx1 vaccine Covishield followed by BBV152 Covaxin Safety and immunogenicity of an inactivated SARS-CoV-2 vaccine, BBV152: interim results from a double-blind, randomised, multicentre, phase 2 trial, and 3-month follow-up of a double-blind, randomised phase 1 trial. The Lancet Infectious Diseases An in vitro and in vivo approach for the isolation of Omicron variant from human clinical specimens. bioRxiv The authors would like to gratefully acknowledge the staff of ICMR-NIV, Pune including Ms. No competing interest exists among the authors.