Fact check: Breakthrough COVID infections

"Breakthrough infection in a care home — 15 infected, two dead." Headlines like these are making many people nervous, and spreading alarm. Are the coronavirus vaccines less effective than initially thought?

When someone who is fully vaccinated comes down with COVID-19, and also displays symptoms of infection, it's classified as a breakthrough infection. Instances of vaccinated people who become infected but remain asymptomatic do not fall into this category.

Do breakthrough infections mean the vaccine isn't working?

No. The claims circulating on social media — that breakthrough infections prove vaccinations don't work or are not very effective — are false. What is true is that no coronavirus vaccine developed so far can offer 100% protection.

According to a study by the CDC, the American health authority, "meta-analyses [from international real-world studies] indicate an average effectiveness of full vaccination against SARS-CoV-2 infection of 85%–95% shortly after completion of vaccination. However, many of the studies in these reviews were conducted prior to the emergence of the variants of concern." With regard to the delta variant, one US study concluded that, on average, the COVID vaccine protects up to 86% of people from hospitalization.

The fact that COVID vaccines aren't 100% effective also means that some fully vaccinated people — the remaining percentage — will nonetheless get sick, may require hospitalization or may even die of COVID-19. Nonetheless, as the CDC points out, studies have shown that "vaccinated people are 8 times less likely to be infected and 25 times less likely to experience hospitalization or death."

Time is also a factor in vaccine protection. "So far, there are no people who have been vaccinated for more than one year. So we cannot yet say precisely how long the vaccine protection lasts," Christine Falk, the president of the German Society for Immunology (DGfI), explained in a DW interview. What is now known, she said, is that antibody levels will fall somewhat six to nine months after vaccination.

However, although the degree of protection against infection is reduced over time, protection against serious illness remains. On October 14, the weekly report by the Robert Koch Institute (RKI), Germany's disease control center, stated that only 0.6% of the 80,181 probable breakthrough infections identified in Germany since February 1 had required treatment in an intensive care unit. The death rate for patients with probable breakthrough infections is 1%.

By way of comparison, during the first wave of infection in Germany, when no vaccines had yet been developed, the RKI estimated that the mortality rate — the proportion of all those who fell ill with COVID who died — was around 6.2%.

The RKI report also said: "Of the total 817 breakthrough cases of COVID-19 cases who died, 606 (74%) were aged 80 and above. This reflects the generally higher risk of death for this age group, irrespective of vaccine efficacy."

Has the number of breakthrough infections increased?

Yes. In some countries where many people have already been vaccinated against COVID-19, the number of breakthrough infections is also increasing — including in Germany. However, the RKI said this development was "to be expected, as more and more people are vaccinated and SARS-CoV-2 is currently spreading again. This increases the likelihood of a fully vaccinated person coming into contact with the virus."

According to the RKI, the week from October 4 to 10 saw an additional 12,520 breakthrough infections. In the previous week, there were 10,824.

Suspected breakthrough infections among symptomatic COVID cases in the 18-59 age group are now at 8.2%, if one looks at the entire period since the beginning of the vaccination campaign in Germany. Looking only at the last four weeks, to October 10, the percentage is considerably higher, at 31.6%. The proportion of vaccinated patients in this age group who have required intensive care treatment is 2.6% since the start of the year, but over the four weeks to October 3 it was a much higher average of 10.1%.

Increases have also been observed in the over-60 age group. The proportion of breakthrough infections among symptomatic COVID cases is 11.7% for the entire period since the start of the vaccination campaign. However, looking only at the four weeks ending October 10, that figure rises to 55.4% of symptomatic cases. The proportion of vaccinated COVID patients over 60 requiring intensive care unit treatment is 7% since the beginning of the year, and 28.8% for the four weeks to October 10.

How much does vaccine protection decrease over time?

The degree of protection people acquire from vaccination will decline over time, but it will do so at different rates in different people, because there are several contributing factors. These include age, preexisting conditions, the interval between vaccinations and the type of vaccine itself.

In particular, compared to other population groups, vaccine protection declines faster in the elderly and the very old, as well as in cancer or transplant patients.

Some countries, such as the United States, the United Kingdom, Israel and Germany, have therefore already recommended that certain groups should receive a third vaccination as a booster. Staff in health care facilities or hospitals will also be offered a third vaccination. More than 1 million people in Israel have already received a third dose.

The length of the interval between the first and second COVID vaccinations may also have an impact on their effectiveness. In Israel, for example, where the majority of the population was vaccinated with BioNTech-Pfizer, the gap between the first and second vaccinations was only 21 days.

As immunologist Christine Falk explained: "The second vaccination is extremely important for creating an immunological memory. The protective function is based on this memory." For this to be effective, she said, longer intervals are better — "so, six weeks with BioNTech instead of three, or 12 instead of six weeks with Astra[-Zeneca]."

Rachel Baig contributed to this report, which has been translated from German