Results of clinical trials on vaccine efficacy revealed that Pfizer-BioNTech had 95% efficacy at preventing symptomatic COVID-19 infection in people without prior infection. 22, 23 Israel was far ahead of other countries in terms of the proportion of vaccinated inhabitants, exceeding 62% at the end of April 2021, with the UK reaching 50% and the USA 42% at the same time. The threshold for COVID-19 ‘herd immunity’ was placed between 60 and 70% of the population gaining immunity through vaccinations or past disease exposure however, scientists warn that herd immunity is unlikely to be achieved owing to factors such as vaccine hesitancy and the spread of new variants.
21 The worldwide vaccination campaign started in December 2020 aiming to provide herd immunity across societies. To control the SARS-CoV-2 spread, a number of different vaccines have been developed and analyzed in clinical trials, including eight vaccines having emergency use or conditional marketing authorizations worldwide or across regions, as of May 2021. 20 The region of Maharashtra, where the B.1.617 variant emerged, experienced a significant rise in daily infection rate after the new variant appeared. 19 Preliminary findings suggest also a significant increase in case fatality rate in young and middle-aged population for the P.1 mutant. 18 Higher incidence of COVID-19 cases in younger age groups was observed in the Amazonas state, suggesting changes in pathogenicity of the P.1 variant. 8, 11, 12, 13, 14, 15, 16 The B.1.351 variant was found to have an increased transmissibility and immune escape 17 and was estimated to be 50% more transmissible than pre-existing variants. 7, 8, 9, 10 An increased risk of transmissibility, hospitalization, and death associated with the B.1.1.7 variant was reported by a number of authors. 6 The disease mortality has been increased in these countries after new variants were developed. 1, 2 Then, several variants of concern (VOCs) have been identified, including B.1.1.7 developed first in the UK in September 2020, 3 B.1.351 in South Africa in December 2020, 4 P.1 in Brazil in January 2021, 5 and the ‘Indian’ variant B.1.617 reported first in Maharashtra in January 2021. EU2 variant (mutation S:447N), first observed in July 2020 in Western Europe, was found to be capable of increasing virus infectivity. During the second half of 2020 and early 2021, a variety of new SARS-CoV-2 variants emerged. The pandemic of the coronavirus infectious disease 2019 (COVID-19) is continuously evolving, driven by the spread of new variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).
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