Recovering from COVID-19 may not offer much protection from future infections, particularly for those with only a mild case, researchers said in the New England Journal of Medicine.
The study analyzed antibodies taken from the blood of 34 patients who had recovered after suffering mainly mild symptoms that didn't require intensive care, according to the report. Just two needed supplemental oxygen and received an HIV medication in an effort to help them battle the disease, and none were on a ventilator or getting Gilead Sciences Inc.'s remdesivir.
The first analysis was done on antibodies taken an average of 37 days after symptoms began, with a second after about 86 days, or less than three months. The researchers determined that antibody levels had fallen precipitously, with a half-life of about 73 days between the two time frames. The loss of antibodies occurred more quickly than with SARS, an earlier type of coronavirus infection. It is likely that the decline will slow with additional time, the authors said.
The findings raise concern that immunity from an infection may not last long in people who develop a mild infection, which accounts for the majority of cases. While the protective role of antibodies against infection with the novel coronavirus isn't fully understood, they are generally considered a good representation of some protection against infection in general, according to the report.
The results call for caution regarding antibody-based "immunity passports," herd immunity and perhaps vaccine durability, especially in light of short-lived immunity against common human coronaviruses, according to the researchers led by F. Javier Ibarrondo, from the David Geffen School of Medicine at the University of California Los Angeles.
The researchers said further studies will be needed "to define a quantitative protection threshold and rate of decline of antiviral antibodies beyond 90 days."
The brief report was in the form of a correspondence letter published in the medical journal.
Thirty of those studied had their infections confirmed via tests for the virus, while the remaining 4 had symptoms and lived with someone who had been diagnosed with the disease, though they weren't personally tested due to a lack of diagnostics early in the outbreak.
