LONDON—A large English study showed the number of people with Covid-19 antibodies declined significantly over the summer, suggesting that getting the virus may not confer long-lasting immunity from future infection.
The survey of 365,000 adults in England who tested themselves at home using a finger-prick test showed the proportion of people testing positive for Covid-19 antibodies declined by 26.5% between June 20—12 weeks after the peak of infections in the country—and Sept. 28.
The results also suggested that people who didn’t display symptoms were likely to lose detectable antibodies before those who had showed symptoms. The study, conducted by Imperial College London and the Ipsos Mori polling organization, was funded by the British government, which announced the results and published the study on Monday night. The results haven’t yet been reviewed by other experts.
Doctors don’t yet know whether antibodies confer any effective immunity against reinfection by Covid-19. But even if they do and the results of this survey are confirmed, it suggests the prospect of widespread long-term herd immunity to the virus will be difficult to achieve. Herd immunity occurs when enough people in a population develop an immune response, either through previous infection or vaccination, so that the virus can’t spread easily and even those who aren’t immune have protection.
The findings showed 18-24 year olds lost antibodies at a slower rate than those aged 75 and over. The smallest decline of 14.9% was of people aged between 18 and 24 years, and the largest decline of 29% was of people aged 75 and over.
The study reflects earlier smaller trials and suggests that antibodies to the virus decline over 6-12 months after infection, as in other seasonal coronaviruses such as the common cold. The study doesn’t indicate whether other types of immune responses—such as that contributed by so-called T cells—would help protect against reinfection.
The study showed 6% of the population of England had antibodies on June 20, compared with 4.4% on Sept. 28. At the end of September, 9% of people displayed antibodies in London, compared with just 1.6% in the least affected region in the southwest of England.
Among ethnic groups, 13.8% of Black people tested with antibodies at end-September and 9.7% of Asians—mainly South Asians. This compared with 3.6% of white people. Minority ethnic groups in the U.K., as in the U.S., have suffered disproportionately from the virus.
The authors admitted the trial had limitations. “It included nonoverlapping random samples of the population, but it is possible that people who had been exposed to the virus were less likely to take part over time, which may have contributed to apparent population antibody waning,” they said.
Write to Stephen Fidler at firstname.lastname@example.org