We know booster vaccinations significantly improve protection against Omicron - but for how long?
According to new research, the high level of protection against the risk of a serious Omicron coronavirus infection requiring hospital treatment begins to drop only a few months after a BioNTech/Pfizer booster vaccination.
"Pfizer BioNTech Covid-19 booster doses significantly improve protection against omicron, although that protection seems to wane after 3 months against emergency room visits, and even for hospitalization," said the study's lead author, epidemiologist Sara Y. Tartof of the Kaiser Permanente Health Consortium in South California. Nevertheless, some efficacy remained even after this time.
For the study, published in The Lancet Respiratory Medicine, researchers analysed 11,123 hospital admissions and emergency department visits that did not result in hospitalisation for an acute respiratory infection. Both the Delta and Omicron variants were in circulation during the research period of December 2021 to February 2022.
The result of the Pfizer-funded study: After three vaccinations, the effectiveness of BioNTech/Pfizer's vaccine against hospitalisation with an Omicron infection was 85% at less than three months. However, it dropped to 55% after three months or longer.
In terms of emergency room admissions, the efficacy of three doses at less than three months against Omicron was 77%, but fell to 53% at three months or longer.
For the Delta variant, trends were generally similar in terms of decline in efficacy against Sars-CoV-2, but at all times efficacy was estimated to be higher than that against the Omicron variant.
The efficacy of the BioNTech/Pfizer vaccine against Omicron was also significantly higher on average after three doses than after two doses.
Officials in some countries are now recommending a second booster for people over 70 and people with certain pre-existing conditions, however the EU Medicines Agency (EMA) stated at the beginning of April that a fourth dose for all citizens was currently not necessary. However, it could make sense for people over 80 years of age in view of the higher risk of a severe infection.