BOSTON — They are the body’s natural big guns when it comes to COVID-19: neutralizing antibodies that should, in theory, kill off the coronavirus.
But new research suggests it doesn’t take long after an infection for those antibodies to retreat -- and that may have implications for long-term immunity to COVID-19.
South Korean scientists looked at around 20 symptomatic and asymptomatic coronavirus patients. They found all had developed neutralizing antibodies two months after infection, but the symptomatic group had a higher amount or titer than the asymptomatic group.
But by five months, levels in both groups had declined.
Between the two groups combined, the mean antibody titer dropped from 219 to 143.
The research appears in the Centers for Disease Control and Prevention publication Emerging Infectious Diseases.
“I wouldn’t say that loss of neutralizing antibodies means those people are all ready to be re-infected,” said Epidemiologist Marc Lipsitch, DPhil., director of the Center for Communicable Disease Dynamics at Harvard School of Public Health. “Whether someone who once had neutralizing antibodies and no longer does has totally lost protection -- it’s unlikely that they’ve totally lost protection. But also it’s possible they’ve lost some of their protection.”
And to some extent, a drop in neutralizing antibody levels with COVID-19 is not surprising. Its predecessor coronaviruses, SARS and MERS, also seemingly left, over time, little in the way of immunological evidence of infection.
“It could be that there’s (SARS and MERS) antibody present but it’s just that it’s not detectable with the tests we can use to detect them,” said David Walt, PhD, a faculty member at Harvard Medical School and in the Department of Pathology at Brigham and Women’s Hospital. “It’s not that they’re not there, necessarily. It may be that they’re at really low levels.”
If that is the case, Walt said the potential remains for a healthy immune response on rechallenge with the virus.
Walt said it’s important to remember the immune system has other options to respond to foreign invaders... including memory B-cells and T-cells which attack virus-infected cells, so even with limited antibodies an immune response is possible.
And what hasn’t even been determined yet is the importance of low antibody levels to COVID-19.
“It’s still unknown whether there’s a correlation between low levels of antibodies and a lack of protection,” Walt said.
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