Coronavirus infection despite vaccination? Maybe, but blows still save lives | Science | Detailed reports on science and technology | DW


Reports of vaccinated people receiving COVID-19 have been in the news again and again in recent weeks, but that is not a reason to get angry or an argument to reject vaccines. Even if someone experiences mild symptoms after a vaccine or tests positive for the coronavirus, the vaccine is still effectively doing what it is supposed to do: preventing severe disease progression and death.

How effective are currently approved vaccines?

All vaccines approved by the health authorities of the European Union (EMA) and the United States (FDA) have shown high efficacy.

For example, the BioNtech-Pfizer and Moderna mRNA vaccines achieve an efficacy of around 95%, while the AstraZeneca vector vaccine reaches 76%, according to recent data. However, this means that it is still possible to get infected after a vaccine.

Still, if efficacy is considered according to the severity of the disease course, all vaccines perform significantly better than without them. In case of infection, for example, vaccines generally prevent the kind of serious reaction that requires people to put on ventilators, or even kill them.

Why have COVID deaths occurred after vaccination?

In Germany, however, there have been some cases where older people in nursing homes still had severe courses of COVID-19 even after vaccination. Some even died.

The Robert Koch Institute (RKI), Germany’s central authority for infectious diseases, writes that two particular circumstances can lead to disease after vaccination, namely whether the infection occurred shortly before vaccination or in the days immediately thereafter.

The reason? It takes the body about two weeks to fully develop immunity. Therefore, full protection is only achieved two weeks after the patient has received their second vaccine injection.

What do sterilizing immunity and functional immunity mean?

When it comes to vaccination, doctors distinguish between sterilizing immunity and functional immunity. Sterilizing means that a vaccinated person can no longer infect anyone. The first evaluations of the BioNTech-Pfizer vaccines administered in Israel showed that people who had been vaccinated twice had a 92% lower risk of infecting other people.

In this regard, it is safe to say that the BioNTech-Pfizer vaccine offers quite high sterilizing immunity against the most common coronavirus variants. Although conclusive figures are not yet available for other vaccines, efficacy is likely to be comparable.

However, only when there is clear evidence that vaccinated individuals cannot infect others, or when a sufficiently high “herd immunity” has been achieved, can the authorities exempt vaccinated persons from obligations such as the use of face masks or the compliance with the rules of physical distancing.

Still, while we haven’t gotten to that point yet, all currently available vaccines have been shown to provide functional immunity – that is, they prevent or reduce the risk of severe symptoms. And even in rare cases of disease occurrence, vaccines have significantly shortened the course of the disease.

How long does a COVID-19 vaccine protect against infection?

So far, there is no clear answer to this question for any of the vaccines. Before vaccines are approved, researchers must determine how safe they are. And in phase III of vaccine development, experts focus on functional efficacy.

But only with time will we know how long immunity from COVID vaccines lasts. That is why the period after vaccine authorization is also known as Phase IV of vaccine development. We are now in the middle of this phase. Reliable statements about the duration of immunity will only be possible after several months or even years.

What are the effects of mutations and variants?

Each vaccine responds differently to viral mutations. At the moment, vaccine developers are concerned about the P.1 variant found in Brazil. This mutant variation has infected numerous people despite having been previously infected or vaccinated. The South African variant B.1.351 can also infect people who have been vaccinated, as medical experts were able to test with the AstraZeneca vaccine.

But here too, doctors assume that vaccines will at least lead to milder courses of the disease and reduce the number of patients requiring intensive care medical treatment.

This has to do with the fact that immunity consists of two components: antibody immunity against the spike protein, in which individual components can mutate, and T-cell immunity, which continues to protect even when antibodies are already they are not that effective.

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