The US Centres of Disease Control and Prevention (CDC) on Friday said that the efficacy of the third doses of the Pfizer and Moderna mRNA vaccines starts falling by the fourth month after being administered, news agencies reported.

The CDC also highlighted that this new finding indicates that additional dose or a fourth dose may be required to enhance protection. While countries are yet to achieve the fully vaccinated target, which means vaccinating citizens with the first two doses, and only some have rolled out boosters, this finding raises new challenges.

The study was conducted between August last year and January 2022 and was based on more than 241,204 visits to the hospital’s emergency section for Covid-related complications and was also based on 93,408 hospitalizations of serious nature.

The study recommended citizens to remain updated with the latest vaccines in order to prevent severe illness and hospitalizations caused due to Covid-19. US president Joe Biden’s top medical advisor Anthony Fauci also highlighted that a fourth dose could be needed to better people who mount weaker immune responses.

Israel earlier in January was the only nation which recommended a fourth dose to all its adults to enhance protection against Covid-19. In Israel, only the elderly, the immuno-compromised and the population over the age group of 60 years are the only ones who are eligible for the fourth dose.