Study shows: Single vaccination hardly helps against delta variant

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Severe changes caused by mutations so that antibodies no longer recognize them: So-called immune escape variants are a bugbear in the Corona pandemic. Now there is new data on Delta.

The delta variant of the coronavirus, which is now also prevalent in Austria, appears to partially escape antibodies of first-time vaccinated and unvaccinated convalescents in laboratory tests. A study in the scientific journal “Nature” provides further evidence of this.

Antibodies can hardly fend off mutant after single dose
In the experiments, the antibodies produced by Biontech/Pifzer and Astrazeneca after a single dose were hardly able to bind to the mutant discovered in India and render it harmless, report researchers led by Olivier Schwartz of the Institut Pasteur in Paris. Both vaccines produced an efficient reaction against Delta only after the second dose – in 95 percent of the individuals (after one dose: ten percent).

According to the study, antibodies in blood samples from unvaccinated convalescents are also less able to bind to delta compared to the previously predominant variant alpha. Following analyses of samples from convalescents who had already received vaccination, the researchers write, the results strongly suggest that such a booster most likely protects convalescents against a variety of circulating viral strains, including Delta.

Antibody levels provide strong indication of immune protection
Results from such laboratory experiments cannot be directly extrapolated to vaccine protection in practice. However, the team of authors writes, the studied levels of so-called neutralizing antibodies would be considered a strong indication of immune protection against symptomatic corona infections. The human immune system not only defends itself against pathogens with antibodies, there is also cellular immunity.

The researchers further report that Delta is resistant to some of the antibody preparations made in the lab, including bamlanivimab. Such therapies are used in some places in high-risk patients at the onset of infection to avert a severe course of covid-19.

The delta variant was first discovered in India and has spread to many countries worldwide. It is considered to be significantly more contagious than previous variants and has been classified as a cause for concern by the World Health Organization (WHO). It has several alterations to the so-called spike protein, which the virus uses to enter human cells.