Delta variant requires higher vaccination rate for herd immunity

The delta variant of the corona virus is causing lockdowns and stricter contact restrictions worldwide. Despite a high vaccination rate, the virus continues to spread – the reason for this is the lower effectiveness of the vaccines against the dominant mutation. Initial studies show that a higher vaccination rate is necessary than for the archetypal variant of SARS-CoV-2.

The Baden-Württemberg Ministry of Health commissioned the study.

Delta variant affects vaccine efficacy

The vaccines against  COVID-19  continue to provide reliable protection against a severe course, but fully vaccinated people are more easily infected with the delta variant of SARS-CoV-2 than with the original type. According to the experts at the Institute for Clinical Epidemiology and Applied Biometry, the effectiveness of the vaccines has decreased by these factors:

  • The vaccination protection of the  Moderna vaccine  is said to have dropped from 82 to 100 percent to 51 to 87 percent.
  • BioNTech/Pfizer vaccine  effectiveness  is said to have decreased from 77 to 95 percent to 54 to 80 percent.
  • AstraZeneca ‘s vector vaccine   also dropped from around 79 percent to 67 percent.

Existing studies also indicate an insufficient protective effect of the single-use vaccine from  Johnson  & Johnson, which is why the Standing Vaccination Commission (STIKO) has already recommended a booster vaccination.

Very high vaccination rate needed for herd immunity

Herd immunity , also known as community protection, can be achieved through a high number of vaccinations or recoveries. Although people primarily protect themselves through vaccination, it also reduces the spread and infection of others with a disease. Vaccination thus also indirectly protects people who have not (yet) received a vaccination. These include, for example, babies and small children or people with certain previous illnesses.

Your own vaccination protection also contributes to the protection of the community. The scientists’ calculations are based on various assumptions, since the effectiveness of the vaccines against Delta cannot be precisely defined.

  • Optimistic assessment: A total of 86.9 percent would have to be vaccinated to prevent the spread of the delta variant despite the lifting of contact restrictions. In addition, the experts assume that around 15 percent have recovered.
  • Neutral assessment: With an average vaccination effectiveness, around 93.3 percent should be vaccinated in order to be able to protect the entire population.
  • Pessimistic assumption: Overall, 100 percent of the population would have to be vaccinated to prevent the further spread of the delta variant.

Booster vaccinations are particularly helpful in protecting older people or people with previous illnesses. However, this effect is only a small factor in achieving herd immunity. It is important to achieve a higher vaccination rate in order to release the health system, prevent the spread as much as possible and reduce the number of severe cases.


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