It’s not just whether someone is immune themselves. The next assumption is that people who have antibodies cannot spread the virus to others. Again, that hasn’t been shown yet.
“We don’t have nearly the immunological or biological data at this point to say that if someone has a strong enough immune response that they are protected from symptoms, … that they cannot be transmitters,” said Michael Mina, an epidemiologist at Harvard’s T.H. Chan School of Public Health.
A number of countries have launched large serosurveys, so hopefully we’ll have a better sense soon of the levels of antibodies being generated by individuals who recover from Covid-19 and among the general population. For now, though, there have only been limited data released from a couple small studies.
Scientists in Europe have pointed to strong antibody production in patients within a few weeks of infection. One study found that people were generally quick to form antibodies, which could help explain why the majority of people do not develop severe cases of Covid-19.
But one preprint released this month complicated the landscape. (Preprints have not been peer-reviewed or published yet in a research journal.) Researchers in Shanghai reported that of 175 patients with confirmed #Covid-19, about a third had low antibody levels and some had no detectable antibodies. The findings suggest that the strength of the antibody response could correlate to the severity of infection, though that’s not known for sure. They also raised concerns that those with a weaker antibody response might not be immune from reinfection.
But outside researchers have said that conclusions about immunity can’t be drawn from what the study found. For one, there are different kinds of antibodies, so some might exist that the test wasn’t looking for . Secondly, studies in other coronaviruses have shown that antibody responses vary from person to person, without clear implications for how protected someone is from another infection.
And, researchers say, antibodies are not the only trick the body has to protect itself . Immune cells also form memories after an initial infection and can be rallied quickly should that same pathogen try to strike again, even without antibodies or after antibody levels fade.