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It remains uncertain whether lowering antibodies increases the risk of reinfection.
FILE: A healthcare worker processes a COVID-19 antibody test after obtaining the patient’s blood. Image: AFP
WASHINGTON – Covid-19 prevalence surveys that detect antibody levels to determine whether people have been infected in the past may not be reliable given how quickly these infection-fighting proteins vanish, according to a US government study. USA
It remains uncertain whether lowering antibodies increases the risk of reinfection.
It is believed that if you are exposed to the virus again, most people’s immune systems will produce new antibodies, as well as immune cells that attack and destroy cells that have been infected.
But the new study highlights an important limitation of the “seroprevalence studies” that are being carried out around the world in an attempt to better understand the actual number of people who have been infected by a virus that often causes no symptoms.
The U.S. Centers for Disease Control and Prevention collected blood serum samples from front-line healthcare personnel at 13 hospitals between April 3 and June 19, 2020, and followed approximately two months later.
Overall, 194 of 3,248 participants (6%) had detectable antibodies to SARS-CoV-2 the first time they were tested.
Among the participants who tested positive, 156 agreed to retest, between 50 and 91 days later.
In this group, 94% saw a decrease in their antibody levels, and 28% did not produce enough Covid-19 antibodies to reach a clear threshold that would suggest a previous infection.
“These results suggest that single-time serologic testing likely underestimates the number of people with prior SARS-CoV-2 infection, and a negative serologic test result may not reliably exclude a prior infection,” the authors wrote. .
Participants who had reported symptoms of the disease had higher levels of antibodies initially than those who had an asymptomatic infection and were less likely to fall below the “positive” threshold.
Most people infected with the virus develop antibodies over the next several weeks, but people with a milder or asymptomatic infection develop fewer antibodies.
In addition to helping to quantify how many seroprevalence studies of infections may be missing, the results “challenge the notion of using individual-level serologic test results to designate a prior SARS-CoV-2 infection,” the authors said.
Finally, the study also shows that the window is limited for collecting potentially effective “convalescent plasma” from the blood of patients who have battled Covid-19, they added.
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