The effectiveness of all vaccines against the Delta variant of SARS-CoV-2 is significantly lower, making a vaccination rate of 90 percent necessary to achieve herd immunity. Several studies have shown that the efficacy of vaccines against the Delta variant is much lower than against earlier strains of the virus, particularly in terms of protection against infections that significantly influence the spread of the virus. Martin Eichner from the Institute of Clinical Epidemiology and Applied Biometry at the University of Tübingen has investigated the impact of this on the necessary vaccination rate to achieve herd immunity. According to a publication by the Ministry of Social Affairs, Health and Integration of Baden-Württemberg, the efficacy of BNT162b2 from BioNTech has decreased from 77-95 percent to 54-80 percent. The protective effect of mRNA-1273 from Moderna and AZD1222 from AstraZeneca against the Delta variant is also significantly lower.
The scientists at the University of Tübingen used three efficacy values of 60 percent (pessimistic), 70 percent (average), and 80 percent (optimistic) for their calculations. They found that, under the optimistic assumption, a vaccination rate of 86.9 percent is necessary to prevent the spread of the virus if 15 percent of the population has already recovered from an infection and there are no contact restrictions. With an average vaccine efficacy, a vaccination rate of 93.3 percent is required, and with a pessimistic assumption, a vaccination rate of 100 percent is necessary. If only 70-80 percent of the population gets vaccinated, herd immunity would only be achieved within a year if there is a very high 7-day incidence rate between 400-800 per 100,000 inhabitants. However, this is not expected in Germany according to current data.
According to the epidemiologist, booster vaccinations are useful for better protecting older and pre-existing conditions individuals and preventing outbreaks in nursing homes. However, they have only a minimal impact on the transmission situation in the general population. In conclusion, the Delta variant poses a significant challenge to achieving herd immunity, and a high vaccination rate is necessary to prevent the spread of the virus.
