The lowdown: Immunity to covid-19 may be short-lived, according to a new longitudinal study of people who have caught the disease and recovered.
The study: Researchers at King’s College London repeatedly tested 96 patients and healthcare workers at Guy’s and St Thomas’ NHS foundation trust for antibodies between March and June. All of the participants were confirmed to have had covid-19, either via a PCR test or a positive antibody test. The researchers found that levels of virus-fighting antibodies peaked about three weeks after symptoms started, then rapidly fell away. Although 60% of participants produced a “potent” antibody response while they had covid-19, only 17% had the same level of potency at the end of the three-month testing period. Antibody levels were higher and longer-lasting in people who had had more severe cases of covid-19. For some milder cases, it was impossible to detect any antibodies at all at the end of the three months. The research is published in a pre-print paper in medRxiv, which means the findings have yet to be subject to peer review.
What it means: The study raises the prospect that, like other coronaviruses, covid-19 could reinfect people repeatedly. If that’s the case, “herd immunity” may never arrive, either through a one-shot vaccine or through community spread of the virus, as any protective antibodies would wane with time. However, antibodies are not the only way people can fight off covid-19. T cells, which seek and destroy cells infected with SARS-CoV-2, could also provide some protection. In short, we are not yet far along enough into this pandemic to have been able to generate enough data from patients to be able to draw conclusions on immunity with a high degree of certainty. There have been anecdotal reports of people catching covid-19 for a second time, but none have been confirmed.