Antibody levels decline after 2 months, CDC finds

COVID-19 antibody levels declined within two months in 156 front-line healthcare workers involved in a CDC study published Nov. 27. 

Researchers collected blood samples from 3,248 front-line healthcare professionals between April 3 and June 19. The healthcare employees worked at 13 hospitals in 12 states. 

Overall, 194 participants had detectable antibodies at the beginning of the study. Among the 156 employees who repeated testing, 93.6 percent saw antibody levels decline within 60 days. Twenty-eight percent of healthcare workers saw antibody levels drop to below the threshold for positivity.

Healthcare workers with higher initial antibody levels were more likely to have detectable antibody levels on repeat testing, compared to those with a low initial response. 

"These results suggest that a substantial proportion of persons infected with SARS-CoV-2 might have negative serologic test results in the months following infection," the CDC said. "Cross-sectional seroprevalence studies that estimate the number of persons who have been infected with SARS-CoV-2 will likely underestimate incidence." 

The CDC added that the study didn't assess whether the antibody declines resulted in a loss of protective immunity.

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