July 15, 2020 -- After people contract SARS-CoV-2, the coronavirus that causes COVID-19, they develop natural antibodies and immunity, although that immunity may decline within months, according to a new pre-print paper. The study was released on medrxiv.org on Saturday and has not yet been peer-reviewed.
Antibody responses began to decline about 20 to 30 days after symptoms started, according to the UK researchers from King’s College London and Guy’s and St. Thomas’ Hospital in London. They also found that the antibodies were higher among those who had more severe disease.
“This study has important implications when considering protection against re-infection with SARS-CoV-2 and the durability of vaccine protection,” they wrote.
The research team tested samples from 65 COVID-19 patients up to 94 days after symptoms started and 31 health care workers who had antibody tests every 1 or 2 weeks between March and June. They found that the “peak” antibody responses happened around 23 days after symptoms began and declined until about 40-50 days after symptoms started.
Some antibodies remained 50-80 days after symptoms started, the authors wrote, but additional studies are needed to understand whether levels plateau or continue to fall.
Antibodies for other human coronaviruses tend to decline over time, too, the researchers wrote, and can last for a few months to a couple of years. The differences are likely related to the variation in symptoms and severity of disease that people experience, they wrote. For instance, antibodies for seasonal coronaviruses associated with the common cold tend to decline quickly and lead to reinfection.
Researchers still need to understand more about the antibody response to SARS-CoV-2, they said, which would influence vaccine clinical trials. Even if antibody levels decline, people may still have some protective immunity. Likewise, so-called “memory immune” cells such as T cells and B cells could remember the infection and reignite the immune system again but lead to a milder infection.
“As time has passed since the SARS-CoV-2 virus emerged, a degree of ‘COVID caution fatigue’ appears to be developing,” James Gill, MD, of Warwick Medical School, said in a statement released by the UK Science Media Centre on Monday. Gill wasn’t involved with the study.
The pre-print study “potentially gives a warning shot to those who have been found to have antibodies to COVID yet have only had mild, if any, symptoms,” Gill said. “We should NOT be surprised if any protective benefit is mild, or at least transient.”