The two studies will shed some light on the duration of immunity following infection with COVID-19, a question that has haunted scientists since the pandemic began. The research appears to show that IgG antibodies—the virus-specific, slower-forming antibodies associated with long-term immunity disappear within weeks or months after recovery.
While most people who become infected with COVID-19 do produce antibodies, and even small amounts can still neutralize the virus in vitro, according to earlier work, the latest studies were unable to determine if a lack of antibodies leaves people at risk of reinfection.
However, both studies suggest that it could be risky to assume that recovered patients are immune to reinfection, which may have implications for how long to maintain physical distancing restrictions.
The first study
The first study was published on June 16, 2020, on the preprint server medRxiv. Nearly 1,500 coronavirus patients in Wuhan, China were screened for antibodies to COVID-19. Those results were compared to three other groups.
The three other groups included nearly 20,000 members of the general population; more than 1,600 patients hospitalized for reasons other than COVID-19; and more than 3,800 medical workers, whom the authors assumed had “inevitably” been exposed to the virus in its early days, meaning they should have developed antibodies.
The researchers found that while almost 90 percent of COVID-19 patients had antibodies, roughly 1 percent to 5 percent of individuals in the others groups had them as well.
The study’s authors made a big assumption, writing they had concluded that the remaining 10 percent of infected patients with no detectable antibodies, combined with the lack of antibodies in healthcare workers, suggests that “after SARS-CoV-2 infection, people are unlikely to produce long-lasting protective antibodies against this virus.”
Keep in mind that this does need to be further studied, particularly the assumption about virus exposure to healthcare workers without confirmed positive tests. It is dangerous to draw conclusions based on a low proportion of antibodies in any particular group without knowing for sure how many were actually infected with the virus.
The second study
The second study, published in the journal Nature Medicine on June 18, 2020, focused on 37 asymptomatic and 37 symptomatic patients.
This particular study noted that over 90 percent of both groups showed steep declines in levels of SARS-COV-2 IgG antibodies within 2 to 3 months after the onset of infection. Additionally, this study showed that 40 percent of the asymptomatic group tested negative for IgG antibodies 8 weeks after they were released from isolation, compared to 13 percent of the symptomatic patients.
“Overall, these results are interesting and provocative but more research is needed, following large numbers of people over time,” Daniel Davis, an immunologist at the University of Manchester, tells Newsweek. “Only then will we clearly know how many people produce antibodies when infected with coronavirus, and for how long.”
Taking into account the cellular immune response
In the studies, the researchers did not into account the protection immune cells offer in fighting the virus on their own or making new antibodies when the virus invades. A few studies have shown that the coronavirus stimulates a robust and protective cellular immune response.
“Most people are generally not aware of T cell immunity, and so much of the conversation has focused on antibody levels,” said Angela Rasmussen, a virologist at Columbia University, according to the New York Times.
Besides T-Cells that can fight the virus, some people who have been infected make so-called memory B cells, which can also speed up antibody production when needed.
“If they find the virus again, they remember and start to make antibodies very, very quickly,” said Florian Krammer, a virologist at the Icahn School of Medicine at Mount Sinai, who has led several studies of antibodies to the coronavirus.
Krammer points out that in the new study, antibodies to one viral protein dropped below detectable levels, however, antibodies targeting the so-called spike protein of the coronavirus — needed to neutralize the virus and prevent reinfection — were still present.
“In fact, these antibodies seemed to show a smaller decline in asymptomatic people than in symptomatic people. The neutralizing antibody is what matters, and that tells a very different story,” Dr. Krammer said.
