In the period from 1 February 2022 to 19 April 2022, vaccine effectiveness of the basic series of COVID-19 vaccinations in preventing hospital admission was 30%. After the booster jab, that percentage was 79%. Vaccine effectiveness against ICU admission was 38% after the basic series, compared to 89% after booster vaccination. This means that the risk of hospital admission after a booster jab is more than 3 times lower than for people who have only received the basic series of vaccinations. The protection provided by the COVID-19 booster vaccination does wane somewhat over time. In people aged 70 years and older, the repeat vaccination seems to restore vaccine effectiveness against hospital admission to the level just after the booster vaccination. It is not yet possible to assess this in younger age groups, since not many people have been admitted to hospital. 

The decrease in vaccine effectiveness in preventing hospital and ICU admission after the booster jab can probably be largely attributed to waning effectiveness over time. Another partial explanation could be that many people who were not vaccinated against COVID-19 have had a SARS-CoV-2 infection by now, and have built up immunity as a result. The difference in the risk of hospital admission for vaccinated and unvaccinated people may grow smaller as a result.

In the period from 1 February 2022 to 19 April 2022, less than 10% of hospital admissions were caused by the BA.2 subvariant of Omicron; that percentage has now risen to more than 90%.