A prospective study of 3,249 Marine recruits—who were mostly male and between the ages of 18 and 20—shows a significant risk of reinfection among those who have antibodies to SARS-CoV-2, the virus that leads to COVID-19.
The study, posted on MedRxiv, was led by researchers at the Icahn School of Medicine at Mount Sinai working with the Naval Medical Research Center. It found that the risk of reinfection in those with antibodies was 18 percent of the risk of infection in those without antibodies. Most of the reinfected Marines were asymptomatic, and none required hospitalization. The infections were detected by PCR tests.
The findings support the importance of vaccinating all segments of the population, including individuals who have SARS-CoV-2 antibodies but were never actually diagnosed with COVID-19, and those who were diagnosed, recovered, and think they are now safe from another infection. The study also points to the fact that young people, who are typically asymptomatic, may unknowingly spread the disease to others more than once.
“It is important that we don’t neglect this college-age group of the population,” says the study’s lead author, Stuart Sealfon, MD, the Sara B. and Seth M. Glickenhaus Professor of Neurology, Neuroscience, and Pharmacology and Systems Therapeutics at Icahn Mount Sinai. “They are such an important group in spreading the disease. Many young people have this ‘get it and get over it mentality’ and unfortunately they still have a surprisingly high risk of recontracting it and possibly spreading the virus to others.”
The six-week study was highly controlled. It involved two separate periods of quarantine and multiple tests for COVID-19 before the recruits entered basic training at Marine Corps Recruit Depot, Parris Island, in South Carolina. The study found that among those with antibodies, the reinfected individuals had lower antibody levels and more often lacked detectable levels of the virus-neutralizing antibody activity that blocks infection.
According to Dr. Sealfon, the findings should help resolve any concerns over whether people who have already had COVID-19 should receive the vaccine, particularly in light of current vaccine shortages.
Stuart Sealfon, MD,
“That’s an important take-home message,” says Dr. Sealfon. “Certainly we can show from this study that there’s a fairly high risk of reinfection and not everybody who has had infection will generate effective immunity. So you really want to vaccinate everyone and not worry if they’ve had it or not.”
Why some people fail to generate persistent immunity against reinfection from COVID-19 remains unknown. But highly variable responses to any disease are actually beneficial for evolution.
“When a new disease shows up, individual immune responses are variable to ensure survival at a population level,” says Dr. Sealfon. “People have different genetics that make up their immune systems. They have different previous exposure histories that train the immune system in how to respond to new infections. Immunity uses combinatorial systems to hedge its bets to try and generate the best response it can within an individual and to vary what’s happening across individuals. As a result of individual differences, some people generate more effective long-term immune responses than others.”
In the November 11, 2020, issue of The New England Journal of Medicine, Dr. Sealfon published an earlier study of these marine recruits during their initial supervised quarantine period. He showed that strict public health measures including wearing face masks, social distancing, hand washing, and widespread testing did not completely suppress transmission of SARS-CoV-2.