A group of American scientists collected blood samples from 72 people in whom the coronavirus was confirmed by PCR testing. Only two study participants had an asymptomatic infection, 18% had a mild course of COVID-19, 67% had a moderate course, another 12% were seriously ill and needed hospitalization.
All blood samples were tested for the presence of an immune response using various test systems at least three weeks after the patients had disappeared from all symptoms of the disease. The results showed that only 46 out of 72 people developed neutralizing IgG and IgA antibodies to coronavirus. The amount of antibodies was very different, some of the participants had them slightly higher than the reference values, some had the maximum concentration. Similar results were obtained when scientists separately identified antibodies to the receptor binding domain (RBD) and nucleocapsid (N) of the coronavirus.
The study authors also found that people who did not develop an immune response were, on average, 10 years younger than the participants with antibodies, and all had very low viral load in the nasopharynx, as shown by PCR testing.
“This suggests that patients with a low SARS-CoV-2 viral load in the airways are less likely to develop a systemic antibody response. People who have suffered from COVID-19 may think that they do not need vaccinations because they are protected, but our results warn against this assumption, ”the scientists wrote.
The study was conducted on a limited cohort of people and its results cannot yet be interpreted for a wide population, but they are consistent with the findings of other scientific works, which showed that not all patients who have recovered from the disease develop antibodies. So, in an Israeli study with the participation of 698 people, 5% remained seronegative. This figure was even higher when testing New Yorkers – 20%. In another study from Germany, 85% of asymptomatic patients were free of antibodies.