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People who develop antibodies after becoming infected with the coronavirus may not keep them more than a few months, especially if they showed no symptoms to begin with, a Chinese study shows.
Previous studies had found that most people who became infected developed antibodies. Health departments around the world give antibody tests as a way to prove a person has already had the coronavirus.
Scientists in the Wanzhou district of China studied 37 people who became infected with the coronavirus and showed symptoms and 37 people who became infected and showed no symptoms, according to the study published in the online journal Nature Medicine.
Eight weeks after recovery, antibody levels fell to undetectable levels in 40% of asymptomatic people and 13% of symptomatic people, Nature Medicine said.
The researchers noted that only a small group of people were studied and that the human body can also use T cells to kill the virus and B cells to produce new antibodies, Business Insider reported. Neither T cells nor B cells were measured in the new study.
Business Insider reported that the researchers tested for two types of antibodies: immunoglobulin G (IgG) and immunoglobulin M (IgM). IgG usually develops over a longer time period, meaning it’s a better indicator of long-term immunity, Business Insider said.
The decrease in detectable antibodies was sharp after 8 weeks, with a 71% median drop for IgG levels in the asymptomatic group and a 76% median drop in the symptomatic group, the study said.
The findings call into question the idea of “immunity passports,” which some countries want to issue to people who test positive for antibodies. These people would be allowed to go back to work and travel because they’re supposedly immune to the virus.
“Together, these data might indicate the risks of using COVID-19 ‘immunity passports’ and support the prolongation of public health interventions, including social distancing, hygiene, isolation of high-risk groups and widespread testing,” the authors wrote.