[Efficacy of Homologous and Heterologous Vaccine Applications on SARS-CoV-2 Omicron Variant: Cohort of Manisa Celal Bayar University Healthcare Workers]. / Homolog ve Heterolog Asi Uygulamalarinin SARS-CoV-2 Omicron Varyanti Üzerindeki Etkililigi: Manisa Celal Bayar Üniversitesi Saglik Çalisanlari Kohordu.

This study was aimed to determine the efficacy of homologous (only CoronaVac or only Pfizer-BioNTech) and heterologous (CoronaVac and Pfizer-BioNTech) vaccines during the period when the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) Omicron variant was dominant in Türkiye. Coronavirus disease-2019 (COVID-2019) infection was confirmed by reverse transcriptase polymerase chain reaction and data on vaccination status against COVID-19 were evaluated during the period of 15 January 2022-1 May 2022 when the SARS-CoV-2 Omicron variant was dominant among 1854 employees followed in the SARS-CoV-2 Vaccine Cohort of Manisa Celal Bayar University (MCBU) Hospital Health Workers. Two separate reference groups were used in the evaluation of vaccine efficacy: those who were never vaccinated and those who received only two doses of CoronaVac. The efficacy of homologous and heterologous vaccine models was evaluated with relative risks and attributable risk percentages. MS Excel, SPSS 23.0 and STATA 14.1 package programs were used for statistical analysis. The mean age of the participants was 36.6 ± 10.0. During the period from January 15th to May 1st 2022, 372 hospital workers were infected with COVID-19. Taking the never vaccinated as the reference group, the most effective model was found to be only the three or more doses of the Pfizer-BioNTech primary vaccination model (85.8%, 95% CI= 40.7-96.6). Models consisting of a single dose of CoronaVac (6.5%, 95% CI= -56.3-44.2) or a single dose of Pfizer-BioNTech (17.7%, 95% CI= -30.2-48.0) booster dose administered after two doses of primary CoronaVac vaccination was not found to be effective against the SARS-CoV-2 Omicron variant. When only two doses of primary CoronaVac vaccination model was taken as the reference group, the model consisting of two doses CoronaVac followed by two Pfizer-BioNTech booster doses was effective as 38.4% (95% CI= 15.4-55.3), whereas three doses of Pfizer-BioNTech booster model was effective as 56.4% (95% CI= 33.9-71.3). To conclude, none of the models other than the homologous or heterologous vaccine models containing at least three doses of Pfizer-BioNTech vaccine were effective compared to those unvaccinated. Compared with those who received only two doses of primary Coronavac, models with at least three doses of Pfizer-BioNTech reminder doses were more effective against the Omicron variant than other models.