(ats) This effect is now well known following two doses of vaccines, but has been little studied following the third injection. The study examined 93,000 hospitalizations and more than 240,000 Covid-19-related visits to emergency departments in ten US states.
It was conducted between the end of August 2021 and January 2022, covering both waves related to the Delta and Omicron variants. During both periods, the effectiveness measured following a third dose was always higher than following two doses, noted the Centers for Disease Prevention and Control (CDC), which publishes this study.
Once Omicron became the dominant variant, efficacy once morest hospitalizations was 91% for those who received their third dose within two months, but fell to 78% for people who received it four months and more ago. A percentage that “remains high”, according to the CDC.
Also following the arrival of Omicron, the effectiveness of the booster dose once morest emergency room visits was 87% within two months, 66% following four months and only 31% over five months later. The CDC notes, however, that this latest figure is “imprecise”, due to the small number of people in the study who received their third dose more than five months ago.
Overall, these results “reinforce the importance of additional considerations for additional doses, in order to maintain or improve protection once morest Covid-19”, write the CDC.
During a press conference on Wednesday, Dr. Anthony Fauci, adviser to the White House on the health crisis, had estimated that it was possible that vulnerable people, such as the elderly or immunocompromised, will in the future need a fourth dose.
