Infected despite immunity: Why breakthroughs don’t surprises experts

Many of us have been hearing of more and more breakthrough cases in recent weeks – friends of friends, celebrities and government figures are testing positive for coronavirus despite being fully vaccinated.

Some get Covid-19 symptoms, albeit mostly mild. In Germany alone, 117,763 probable 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 see a lack of effectiveness of vaccines, which continue to protect very well 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.

The best protection is one to two weeks after the second vaccination, after which the protection against infection slowly decreases, Sander says. However, vaccinated people remain much better protected than unvaccinated people.

While many are surprised at the fact that the coronavirus is still a threat to those who are vaccinated, this diminishing level of immunity is not unexpected in the scientific community.

Leading German virologist Christian Drosten said in April that vaccinated people could contribute to the transmission of the virus again after a few months.

Much more important than being safe from infection, however, is a protection against a severe case of Covid-19 – which remains stable, emphasises Streeck.

According to experts, those who become infected despite vaccination are usually mildly ill or do not notice anything. In general, vaccine breakthroughs also occur with vaccinations against 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 particularly dangerous in older people or those with previous illnesses. The immune response of 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 the beginning of February and the end of last week 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 hospitalised, 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 is able to 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 programmes have helped immunize the majority of the country are now keen to maintain that level of immunity with booster jabs. And yet some experts are worried the level of trust in vaccines will suffer if there were 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.

Opponents of an expansion of booster vaccinations, including Streeck, point to the worldwide shortage of vaccines, and stress that the majority of countries still need doses more urgently than those where booster vaccination are an issue.

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