A few months ago, a COVID-19 outbreak in a retirement home may have been a simple disaster. As it is, an outbreak in Germany has turned into a real-world acid test for COVID-19 vaccines. It's a disaster, but one from which scientists and society can learn.  

In Leichlingen, near Cologne, 17 people including residents and staff at a retirement home have been infected with the novel coronavirus. Fourteen of those people have been fully vaccinated. At time of writing, those who had tested positive for the virus reported mild symptoms or no symptoms at all.

What the outbreak appears to show is that coronavirus vaccines do not necessarily stop a person becoming infected with COVID-19, but that they do prevent the most severe symptoms. Germany's vaccine authority, the Robert Koch Institute, says that would be true for the BioNTech-Pfizer vaccine in about 95% of cases. 

And in that sense, the vaccine appears to be working exactly as predicted. So far, it has successfully saved infected residents and staff members from worse, and potentially fatal, symptoms. But some researchers would like to be able to predict such outbreaks — and the efficacy of vaccines, especially against variants of the virus — even better.

What about the variants?

Reports suggest that the outbreak in the retirement home involves the B.1.1.7 variant. The variant was originally identified in the United Kingdom and has since become a dominant strain around the world, including Germany, where a leading epidemiologist, Christian Drosten, has said "we may as well stop testing for it."

A study in the medical journal The Lancet suggests that the B.1.1.7 variant is not deadlier than the original virus, but it is considered to be more infectious.

Other variants of concern, as they are called, have been detected in South Africa, Brazil and, most recently, one called B1617, which is thought to have caused a sharp rise in cases in India.  

The question on everyone's lips

There has been some concern that the vaccines in circulation, which were developed for the original strain of the virus, SARS-CoV-2, may be less effective against mutated versions of the virus. 

Scientists have tried to assess the situation, using laboratory studies. But the results have been mixed so far.

There are indications that existing vaccines may still be effective against the strain from the UK, but less effective against the one from South Africa.

However, it is difficult to fully replicate "real-world" conditions in a laboratory.

So, researchers in Israel are trying to address that. Their study has become the first to test a vaccine's efficacy against different variants in real-world settings.

Professor Adi Stern of the Shmunis School of Biomedical and Cancer Research at Tel Aviv University was part of the team of researchers who conducted the study.

In an email to DW, Stern said she and her colleagues had found "real world evidence for reduced effectiveness of the BioNTech-Pfizer vaccine against particular variants in specific time windows post vaccination." 

From 'slightly concerning' to 'reassurance'

The researchers "matched" vaccinated and unvaccinated people, according to age, biological sex, ethnic group and location. That was to ensure the most valid comparison possible.

Then they compared the prevalence of different variants amongst vaccinated and unvaccinated people. The researchers wanted to see which variants were more likely to "breakthrough" the barrier of protection offered by a vaccine.

The scientists found that the variant from South Africa was more likely than the UK variant to achieve a "breakthrough" a short time after people had received a second vaccine dose.

Professor Stern describes this reduced effectiveness against the South African variant as "slightly concerning." But she says her study also provides reassurance.

"Overall, our study suggests effectiveness of the vaccine remained very high at two weeks after the second dose against both variants," writes Stern.   

Their findings do not include the P.1 variant from Brazil or the B1617 variant from India as they were not detected in anyone who participated in the study.

The study was a collaboration between Tel Aviv University and Clalit Health Services, the largest health services organization in Israel.