Many of us have been hearing of increased breakthrough COVID-19 cases in recent weeks – friends of friends, celebrities and government figures are testing positive for the coronavirus despite being inoculated.

Some develop COVID-19 symptoms, albeit primarily mild. In Germany alone, 117,763 potential vaccination breakthroughs, i.e. infections with symptoms, were recorded since the beginning of February by the Robert Koch Institute (RKI), leading the country's pandemic response.

And yet, experts do not doubt the effectiveness of the vaccines, which continue to protect against severe symptoms, even if booster vaccinations are needed to maintain this level of protection.

How breakthrough infections occur

"You have to know: the protection against infection is no longer as good six months after vaccination," says virologist Hendrik Streeck. Vaccine researcher Leif Sander from the Charite hospital in Berlin agrees. Sander says that the adequate protection period is one to two weeks after the second dose of vaccine, after which it slowly decreases. However, vaccinated people remain better protected than unvaccinated people.

While many are surprised that the coronavirus is still a threat to those who are vaccinated, this diminishing level of immunity is not unexpected in the scientific community. In April, leading German virologist Christian Drosten said that vaccinated people could contribute to the transmission of the virus again after a few months.

However, much more important than being safe from infection is protection against a severe case of COVID-19, emphasizes Streeck.

According to experts, those getting infected despite vaccination develop mild symptoms or are asymptomatic. In general, vaccine breakthroughs also affect those who have been vaccinated for other diseases. The risk posed by vaccinated and unvaccinated infected persons also differs.

"According to one study, when vaccinated persons become infected, their viral load is briefly as high as that of unvaccinated persons," Streeck explains. "But this drops much more quickly. Thus, vaccination shortens the time span in which the virus can be passed on."

Vaccine breakthroughs can be dangerous

It's important to know that an infection can be fatal in older people or those with underlying diseases. The immune response in older people, for example, is lower after vaccination, and they can then become more seriously ill.

According to the RKI, 782 of the 1,076 COVID-19 cases with vaccine breakthroughs that died between February and October were at least 80 years old.

"This reflects the generally higher risk of death – regardless of vaccine efficacy – for this age group," it says.

The share of vaccine breakthroughs in all COVID-19 cases shows, "that only a small proportion of hospitalized, ICU-attended or deceased COVID-19 cases can be assessed as vaccine breakthroughs."

The RKI calls the increase in breakthrough infections over time "predictable" – more and more people are vaccinated, and the virus can spread more again as restrictions end.

"This increases the probability of coming into contact with the virus as a fully vaccinated person."

Experts, where vaccination programs have helped immunize the majority of the country, are now keen to maintain that level of immunity with booster jabs. However, some experts worry that people will not trust the efficacy of vaccines if there is a widespread call for boosters now.

And yet, for Charite scientist Sander, "offering all vaccine-ready people a third vaccination six months after the second vaccination would also have a dampening effect on the spread of the virus in the population."

Sander also cites Israel's recent experience, where they "boosted" themselves out of the past wave.

Those not in favor of booster vaccinations, including Streeck, point to the worldwide shortage of vaccines and stress that most countries still need doses more urgently than those where booster vaccination is an issue.

In addition: The health system would be more relieved if vaccination gaps were closed for people over 60 – and less with third vaccinations for people in their mid-20s.