An American study was published today. According to the study, different booster doses prevent severe cases of the disease.

The in-depth study by the Centers for Disease Control and Prevention (CDC) examined data from more than 300,000 emergency room visits, urgent care clinics and hospital admissions in ten states from 26 August 2021 to 5 January 2022.

The study shows that during the period when the Delta variant dominated, vaccine efficacy against Covid-19-related hospitalizations was 90% between 14 and 179 days after the second dose of a vaccine. It fell to 81% more than 180 days after the second dose and to 94% 14 days or more after the third dose.

As soon as the Omicron variant became dominant, vaccine efficacy against hospitalizations between 14 and 179 days after the second dose was estimated at 81%. It was 57% after more than 180 days after the second dose, and 90% 14 days or more after the third dose.

Subsequently, a second study, based on data from 25 US states and local jurisdictions, showed that vaccine efficacy against infection fell from 93% before Delta to about 80% once Delta became dominant. But protection against death remained stable – and high – at 94%.
 
Efficacy against infection fell to 68% with Omicron. The authors were unable to estimate the vaccine’s protection against death during Omicron because of a delay in recording the information, but scientists generally expect it to remain very high.