In the period from 1 February 2022 to 31 May 2022, vaccine effectiveness of the basic series of COVID-19 vaccinations in preventing hospital admission was 23%. After the booster jab, that percentage was 77%; for people over 60 who received a repeat vaccination against COVID-19, vaccine effectiveness against hospital admission rose to 86%. Vaccine effectiveness against ICU admission was 28% after the basic series and 88% after booster vaccination; for people over60 who received a repeat vaccination, that percentage was 87%. 

This means that the risk of hospital admission after a booster jab was more than 3 times lower than for people who have only received the basic series of vaccinations. For people over 60 who received a repeat vaccination, the risk of hospital admission was 1.5 times lower than for people over 60 who had received one booster jab. Since mid-March 2022, hospital and ICU admissions have been decreasing among both vaccinated and unvaccinated people in all age groups. 

This means that the booster jab still helps to prevent hospital and ICU admission due to COVID-19, and continues to be effective after three months. However, we do see that vaccine effectiveness wanes over time. The repeat vaccination against COVID-19 restores vaccine effectiveness to levels comparable to shortly after the booster jab. Looking at the basic series of vaccinations as well as the booster jab, the decrease in vaccine effectiveness in preventing hospital and ICU admission can probably be attributed in part to waning effectiveness over time. Another partial explanation could be that many people who were not vaccinated against COVID-19 still built up immunity as a result of a SARS-CoV-2 infection.