| Since upsurge of coronavirus pandemic in December 2019, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the number of confirmed cases has increased more than 308 million worldwide, with nearly 5 million deaths. Vaccines are best way to control covid-19 pandemic as suggested by researchers all over world. Current COVID-19 vaccines were based on the SARS-CoV-2 spike protein, which virus used to bind and infected host cells. But the emerging “variants of concern” seemed to be more transmissible or deadlier than the wild-type SARS-CoV-2,containedmutations in the spike protein, questioning vaccine efficacy concerns. Multiple vaccines Pfizer-BioNTech, Moderna Sinopharm, Sinovac, Oxford-AstraZeneca, Sputnik V, Novavax have been granted authorization for vaccination against covid -19 in different countries. Despite authorization having been granted for multiple vaccines, as the ongoing global outbreaks demonstrated, the pandemic is far from over. This review discussed mutations in spike proteins and compared effectiveness of mRNA and
AstraZeneca against variants of concern. Vaccine effectiveness was increased ≥7 days after the second dose against Alpha for all three vaccines: mRNA-1273=92% (95% CI, 88–95%), Pfizer=89% (95% CI, 87–90%), and AstraZeneca=91% (95% CI, 62–98%). Efficacies for double dose mRNA vaccines are 84%, 88%, and 77% respectively against both Beta and Gamma variants together in multivariate analysis. Efficacy reported for greater for Beta compared to Gamma variant. Vaccine effectiveness of the two-dose regimen of AstraZeneca after 14 days of the second dose is 77.9% (95% CI, 69.2–84.2) against Covid-19, 87.6% (95% CI, 78.2–92.9) against hospitalization, and 93.6% (95% CI, 81.9–97.7) against death for Gamma variant. The effectiveness of two doses Of Pfizer and AstraZeneca was documented 88.0% (95% CI, 85.3 to 90.1) and 67.0% (95% CI, 61.3 to 71.8) against the Delta variant. There was no effect against Omicron from 15 weeks after AstraZeneca two dose regimens, while VE after Pfizer two dose regimen was 88.0% (95%CI: 65.9 to 95.8%) 2-9 weeks after dose 2, dropping to between 34 and 37% from 15 weeks post-dose regimen.
Keywords: Vaccine efficacy,SARS-CoV-2,AstraZeneca,Pfizer.
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