New evidence of the instability of Covid-19 antibodies, a surveillance exercise conducted by the Centers for Disease Control and Prevention (United States) and the results of which were published in the Morbidity and Mortality Weekly Report indicates that they disappear easily.
93% of people who had Covid-19 antibodies saw their presence decline
Covid-19 antibodies, do they disappear over time? To find out, the study authors measured the presence of Covid-19 antibodies in 3,248 caregivers in 13 hospitals, in April-June 2020, then again 60 days later. Of these 3,248 people, 194 (or 6%) had antibodies. 60 days later, in 146 of 156 people retested (or 93.6%) the presence of antibodies declined, while 44 (or 28.2%) saw their antibodies disappear (or at least decline. below the detection threshold). Notably, during the second test antibodies could be detected in people who had more of them when they were tested the first time.
It is not immediately clear whether this disappearance of antibodies makes people more vulnerable to the risk of reinfection. On the other hand, these results show us that measuring the presence of antibodies in a given population is not a valid method for evaluating the proportion of the population that has already had Covid-19. Conversely, the fact that a person does not have antibodies at time T does not mean that they have never had Covid-19.
Antibodies disappear more in asymptomatic form
It also appears that the decline of antibodies is more characteristic of asymptomatic forms of Covid-19. Of the 108 caregivers who had a symptomatic form of this disease, 21 (or 19.4%) saw their antibodies decline. At the same time, among the 48 caregivers who had tested positive at one time or another for the PCR test without having had any symptoms, 23 (or 47.9%) saw their antibodies decline.