Jan 23, 2022
All WHO-approved COVID-19 vaccines offer protection against severe illness, hospitalisation, and death. Breakthrough infections in vaccinated persons, in most cases, are less severe than those in unvaccinated persons. However, the duration of protection from the vaccines is still unknown and emerging data consistently show a decline in vaccine effectiveness against SARS-CoV2 infection and COVID-19 over time after vaccination, with a more significant decline in older adults. Booster doses are administered to increase or restore protection from all variants of COVID-19. Both homologous and heterologous booster regimens have been found to be immunologically effective. The recommended interval for booster vaccination is 3 to 6 months after the primary series.
As of 22 December 2021, at least 126 countries worldwide have already issued recommendations on a booster or additional vaccinations and more than 120 have started programmatic implementation. The most commonly prioritized target populations for booster doses are older adults, health workers, and immunocompromised individuals.
References:
1. World Health Organization (WHO) Interim statement on booster doses for COVID-19 vaccination, Update 22 December 2021 (https://www.who.int/news/item/22-12-2021-interim-statement-on-booster-doses-for-covid-19-vaccination---update-22-december-2021)
2. The U.S. Centers of Disease Control and Prevention (CDC) Interim Clinical Considerations for Use of COVID-19 Vaccines Currently Approved or Authorized in the United States (https://www.cdc.gov/vaccines/covid-19/clinical-considerations/covid-19-vaccines-us.html)