COVID-19 booster vaccines administration in different countries

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that resulted in the COVID-19 global pandemic had consequently led to the development of different types of COVID-19 vaccines, including the messenger RNA (mRNA) vaccines, inactivated virus vaccines, a protein subunit vaccine, and viral vector recombinant vaccines. Countries worldwide started their national vaccination program as soon as the COVID-19 vaccines got approved by the World Health Organization (WHO) under the emergency use listing. This includes COVID-19 vaccines by Pfizer-BioNTech, Moderna, AstraZeneca, Janssen, Sinovac, and Sinopharm. Findings suggested that protection against COVID-19 provided by these vaccines may be waning or that the protection reduces against variants of concern (VOC) or even inadequate protection of the primary vaccination for some risk groups. This led to the development of the COVID-19 booster vaccine that aims to improve and prolong the protection against COVID-19. This review aims to discuss the various COVID-19 booster vaccines that are being authorized and administered, the eligibility criteria for the different booster vaccines, and the extent of protection these booster vaccines provide in the United States (US), Israel, United Kingdom (UK), Singapore and Chile.