Fewer than 4% of adults in Wuhan, China, tested positive for antibodies against COVID-19, putting the possibility of countries developing “herd immunity” against the virus without a vaccine in doubt, according to an analysis published [October 23] by JAMA Network Open.
The findings also suggest that those who experience mild disease or who have no outward symptoms of the virus may not develop long-lasting immunity to it naturally, the researchers said.
The term herd immunity refers to a scenario in which most of a population has become immune to a virus and these people effectively provide indirect protection to those who are not.
Although some studies have suggested that people infected with COVID-19 develop antibodies — proteins produced by the immune system that help fight off disease — against it that last several months, there have also been cases of reinfection, where someone who has recovered gets sick again with a different strain of the virus.
“What this study shows us is that we need to continue testing people in large numbers — both those with symptoms and without — so we can identify all people with active virus, because even people who don’t have symptoms may be shedding virus,” meaning they’re still contagious, [biostatistician and epidemiologist Henry Raymond] said.