What does it mean to get infected or sick despite Corona vaccination?

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Although even vaccinated people can become infected with the coronavirus, the shot helps them. In any case, they are less likely to get sick.

Received the full Corona vaccine and still infected or even sick: the number of such vaccine breakthroughs is increasing and unsettles many people. But such infections are not a sign that the shots are not working, as experts point out. Vaccinated people would still have a significantly lower risk of falling ill or even dying. In fact, in view of such infections of vaccinated people, it is mainly those who have not yet been vaccinated who need to worry.

More Corona vaccinations, more vaccine breakthroughs
The fact that people can become infected after receiving the Corona vaccine sounds paradoxical at first to laypeople. But to scientists, it’s no surprise. “We knew from the beginning that the vaccine was not 100 percent effective. Even in the approval studies, fully vaccinated people had become infected,” explains Carsten Watzl, an immunologist at the Leibniz Institute for Human Factors Research at the Technical University of Dortmund. That is why it is now more common for even fully vaccinated people to become infected or ill. Such cases are called breakthrough infections or vaccine breakthroughs. The more people are immunized, the more frequently they occur.

Covid-19 makes sterile immunity difficult
Leif Erik Sander, an infectious disease immunologist at Berlin’s Charité University Hospital, also emphasizes that a certain number of such infections were to be expected: “Especially with a respiratory pathogen that infects the upper respiratory tract, multiplies there and is also passed on from there, it is difficult to establish sterile immunity.” Sterile immunity is when both infection with a pathogen and its transmission are completely prevented.

Infected despite Corona vaccination – when do we speak of a vaccine breakthrough?
The Robert Koch Institute (RKI) defines a probable vaccine breakthrough as a Sars-CoV-2 infection with symptoms of disease diagnosed in a fully vaccinated person by PCR or pathogen isolation. Full vaccine protection is assumed when at least two weeks have passed after a completed vaccination series, he said. According to the RKI, there were 13,360 symptomatic vaccine breakthroughs since the start of the vaccination campaign through Aug. 17. Nationwide, 48 million people had been fully vaccinated by then. However, not all of them had passed the two weeks after the last vaccination.

Testing after Corona vaccination
It is not easy to detect infections of fully vaccinated people that are asymptomatic: “Such infections can only be detected by chance, because vaccinated people can hardly be tested,” explains Watzl, who is also secretary general of the German Society for Immunology. And even in the case of symptomatic infections, there is certainly still an unreported number, he adds: “In the case of vaccinated people, there is a likelihood that they do not associate symptoms with Corona, therefore do not see a doctor and do not get tested.”

Course of disease milder after Corona vaccination
In this context, the number of vaccine breakthroughs is an important measure to determine how effective the vaccines actually protect, he said. “Here we see two things: one is that the number of these breakthrough infections is still the smaller part of the total infections, even though the group of vaccinated people is the larger part. And from that, you can infer that vaccination protects against infection.” On the other hand, he said, infections in vaccinated people are much milder.

More “vaccine failures” among over 60s
But there also appear to be vaccine specifics for those over 60. For example, Watzl reports that there are older people who have been vaccinated twice but still have developed little or no immunity. “These individuals are considered vaccinated and protected, but actually have little to no protection and a corresponding risk of becoming severely ill if infected.” The proportion of such “vaccination failures” among the elderly is probably five percent, he said.

Vaccinated individuals can unknowingly spread Corona
“The individual vaccinated is certainly much better protected than a non-vaccinated person, but the latter in turn can no longer rely on being protected because everyone around him is vaccinated,” says Watzl. Sander also warns, especially in light of the delta variant, that vaccinated people could unknowingly spread the virus: “That’s why even vaccinated people should continue to wear a mask in certain areas, such as public transportation, and get tested regularly if they work in sensitive areas.”

Contact with virus acts like vaccination booster
It is quite clear, Sander said, that we will all come into contact with the virus – be it Delta or another variant – by the end of next year: “Either we will have been vaccinated, so that this contact will act like a vaccination booster and we will not notice anything or very little of the infection, or we will be unvaccinated and have a first contact with the virus – and thus the risk of becoming seriously ill.”