The results of a small study by Chinese scientists published in the journal Nature Medicine indicate that immunity of those who recovered after COVID-19 is not very extended, the Business Insider reports.
Researchers tested the antibodies of 37 people who had the coronavirus in Wanzhou, an urban submission area in Chongqing. In addition, 37 people were tested who tested positive for the virus but did not show symptoms during the illness. The study was supposed to answer two key questions: whether most people develop immunity after infection and how long this protection lasts.
As the results showed, antibodies - blood proteins that fight the virus and can prevent re-infection - most patients had enough for only a few months. About eight weeks after recovery, antibodies dropped to undetectable levels in 40% of asymptomatic people and 13% of those who had symptoms. Asymptomatic generally had a weaker immune response, the study authors report.
Is a low antibody level sufficient to provide immunity? Previous studies have shown that there is such a possibility, but there are still many ambiguities on this issue. In any case, the new results make the introduction of “immunity passports” pointless and do not bode well for the development of an effective vaccine.
Nevertheless, the study has weaknesses that do not allow us to accept its results as the only true ones: the sample size is small, and individual antibody tests may not reflect the overall picture. As practice shows, the immune responses to the new coronavirus are very different in different patients.
There is another important limitation. Researchers from Wanzhou tested two types of antibodies: immunoglobulin G (IgG) and immunoglobulin M (IgM). IgM is produced by the body as a result of the first reaction to a viral infection, IgG develops over a longer period of time, therefore it is considered to be the best indicator of long-term immunity. It was he who dramatically decreased in the test participants: after eight weeks, IgG remained at the same level in only three people, and some did not have detectable IgG at all.
However, antibodies are not the only way the human body can fight the virus: it also uses T-cells to kill the virus and B cells to quickly produce new antibodies. Neither one nor the other was measured in a new study.
In the photo, a health worker takes blood from a patient to determine the level of antibodies to COVID -19, Krakow. Photo: Omar Marques / Getty Images