Study shows evidence of waning immunity to Covid-19

Researchers who sent out home finger-prick tests to more than 365,000 randomly selected people in England found a more than 26% decline in Covid-19 antibodies over just three months.

“We observe a significant decline in the proportion of the population with detectable antibodies over three rounds of national surveillance, using a self-administered lateral flow test, 12, 18 and 24 weeks after the first peak of infections in England,” the team wrote in a pre-print version of their report, released before peer review.

“This is consistent with evidence that immunity to seasonal coronaviruses declines over 6 to 12 months after infection and emerging data on SARS-CoV-2 that also detected a decrease over time in antibody levels in individuals followed in longitudinal studies,”

The study was published Monday by Imperial College London and Ipsos MORI, a market research company. At the beginning of the study, in June, 6% of those who took the tests had IgG antibody responses to the coronavirus, they reported. By September, just 4.4% of them did. For health care workers, the rates stayed about the same.

Antibodies are the proteins your body naturally generates to fight infection. IgG are one type – the tests were not designed to detect other types of antibodies. Other research teams have found that other types of antibodies may persist longer than IgG does.

The results also confirm earlier studies that showed that people who did not have symptoms of Covid-19 are likely to lose detectable antibodies sooner rather than those who had more severe infections.

Younger people who had recovered from Covid-19 had a slower loss of antibodies, compared to people older than 75 who had survived an infection, the researchers found.

Still, not enough is known to determine if antibodies provide any effective level of immunity to Covid-19, or how long people may be immune to reinfection with the coronavirus.

Some infections, such as measles, cause what’s known as sterilizing immunity. People infected once have antibodies that can be detected for many years after infection.

With coronaviruses, scientists know less. It’s also unclear what contribution T cell immunity and the body’s memory responses to threats like Covid-19 will play in providing protection if someone is exposed again to the novel coronavirus. More research is needed to better understand the ongoing risks of reinfection.

The study has limits. The samples were not taken from the same people over and over again, but from different people over time. It’s possible people who had been exposed to the coronavirus were less likely to take part over time and that may have skewed the numbers, researchers said.

“This very large study has shown that the proportion of people with detectable antibodies is falling over time,” Helen Ward, who is on the faculty of medicine at the school of public health at Imperial College London, said in a statement.

“We don’t yet know whether this will leave these people at risk of reinfection with the virus that causes COVID-19, but it is essential that everyone continues to follow guidance to reduce the risk to themselves and others,” added Ward, who worked on the study.

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