COVID-19 Herd Immunity Is Much Closer Than Antibody Tests Suggest, Say 2 New Studies

If the findings are true, that's really great news.


The prevalence of immunity to the coronavirus that causes COVID-19 may be much higher than previous research suggests according to an intriguing new study by researchers associated with Karolinska Institute in Sweden. In addition, a new German study by researchers associated with the University Hospital Tübingen in Germany reports that people who have been previously infected with versions of the coronavirus that cause the common cold also have some immunity to the COVID-19 virus. If these reports stand up to further scrutiny, it would be very good news because they suggest that the pandemic could be over sooner and ultimately be less lethal than feared.

First, a few caveats: Both studies are based on small sample sizes and neither have yet been vetted by peer review.

In the Swedish study, researchers not only checked 200 participants for the presence of immunological proteins called antibodies produced in response to COVID-19 infections, but also for T-cells which are another virus-fighting component of the immune system. Detecting and evaluating T-cells is a bit trickier than measuring antibodies.

The Karolinska researchers, according to the accompanying press release, "performed immunological analyses of samples from over 200 people, many of whom had mild or no symptoms of COVID-19." The study tested COVID-19 patients, exposed asymptomatic family members, healthy blood donors who gave blood during 2020, and a 2019 donor control group.

"One interesting observation was that it wasn't just individuals with verified COVID-19 who showed T-cell immunity but also many of their exposed asymptomatic family members," said Karolinska researcher Soo Aleman. "Moreover, roughly 30 per cent of the blood donors who'd given blood in May 2020 had COVID-19-specific T cells, a figure that's much higher than previous antibody tests have shown."

"Our results indicate that roughly twice as many people have developed T-cell immunity compared with those who we can detect antibodies in," noted Karolinska Center for Infectious Medicine researcher Marcus Buggert.

Study co-author Hans-Gustaf Ljunggren told The Telegraph that if the study's findings are replicated, they would apply to any country. London, for instance, might have about 30 percent immunity and New York above 40 percent. If so, some parts of the U.S. are much closer to herd immunity than population-wide antibody testing currently suggests.

Herd immunity is the resistance to the spread of a contagious disease that results if a sufficiently high proportion of a population is immune to the illness. Some people are still susceptible, but they are surrounded by immune individuals who serve as a barrier, preventing the microbes from reaching them. Epidemiologists typically estimate that the COVID-19 threshold for herd immunity is around 60 to 70 percent.

Still the Swedish researchers caution, "It remains to be determined if a robust memory T cell response in the absence of detectable circulating antibodies can protect against [the virus]."

In a second study, German researchers analyzed blood samples of 365 people, of which 180 had had COVID-19 and 185 had not. When they exposed the blood samples to the COVID-19 coronavirus, they found, as expected, that blood from those who had had the illness produced a substantial immune response. More significantly, they also found that 81 percent of the subjects who had never had COVID-19 also produced a T-cell immune reaction, reports The Science Times. If the German study's results prove out, that would suggest that earlier common cold coronavirus infections may provide about eight in 10 people some degree of immune protection from the COVID-19 virus.

The findings in both of these studies are potentially very good news with respect to public health and the course of the COVID-19 pandemic. Here's hoping that future replications will validate them.