By Jacqueline Howard
CNN
February 20, 2022
(CNN)As the world approaches the second anniversary of the declaration of the Covid-19 pandemic by the World Health Organization, on March 11, more nations are rolling out — or are discussing the possibility of — fourth doses of coronavirus vaccine for their most vulnerable. In the United States, leading public health officials say they are “very carefully” monitoring if or when fourth doses might be needed.
Fourth vaccine dose boosts antibodies, researchers say, but likely not enough to prevent Omicron breakthrough infections
Israel was the first nation to roll out fourth doses, announcing in December that adults 60 and older, medical workers and people with suppressed immune systems were eligible to receive the extra shot if at least four months have passed since their third dose.