Asymptomatic COVID-19 patients have weaker immune response, China study finds

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Asymptomatic coronavirus patients have a weaker immune response to the virus, according to a China study.

The findings of the study, which has not been throgh a rigorous peer review process, were published on the pre-print website medRxiv.

Scientists examined the blood samples of 1,470 COVID-19 patients in three hospitals in Wuhan, China, the first epicenter of the pandemic, to determine if they had antibodies for the virus. They also assessed the blood of 3,832 health care providers who did not test positive for the coronavirus from three hospitals in Wuhan.

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The team found that 89 percent of hospitalized COVID-19 patients had virus-specific antibodies against the coronavirus, compared with 4 percent of health care workers and the general population, and 1 percent of non-COVID patients.

"These data suggest that asymptomatic individuals had a weaker immune response to SARS-CoV-2 infection," lead author Ai-Long Huang from Chongqing Medical University told The Daily Mail.

However, the study also revealed COVID-19's ability to cause lung abnormalities, even in asymptomatic patients, as University of Washington Biology Professor Carl Bergstrom noted.

Antibodies are usually detectable about seven days after a person is infected, while virus-specific antibodies can take around two weeks, according to research cited by the scientists. The participants had antibody tests from February 29 to April 29.

According to scientists, the 10 percent of COVID-19 patients in the study who didn't have antibodies 21 days after their symptoms started probably "lost" them after recovering from the illness.

"The data are in line with several recently reported studies suggesting that those with mild or asymptomatic infections make a less robust antibody response to SARS-CoV-2 than those with more severe disease," Eleanor Riley, a professor of infectious disease at Edinburgh University who was not involved in the study, told the British publication.