The antibody response to the Covid-19 virus declines over time, according to a new analysis published Tuesday based on fingerstick tests in more than 365,000 randomly selected people in England.
Tests conducted at home between June 20 and September 28 found that the number of people who tested positive decreased by 26.5% during the study period, said the researchers led by Imperial College London.
The downward trend was seen in all areas and age groups, but not in healthcare workers, which could indicate repeated or higher initial exposure to the virus, the authors suggested.
The decrease was greater in people 75 years of age and older compared to younger people, and also in people with suspected rather than confirmed infection, indicating that the antibody response varies with age and severity of the disease, said the university.
Paul Elliott, program director at Imperial College, said: “Our study shows that over time there is a reduction in the proportion of people who test positive for antibodies. A positive antibody test does not mean that you are immune to Covid-19. ”
“It is not clear what level of immunity the antibodies provide, or how long this immunity lasts. If someone tests positive for antibodies, they should still follow national guidelines that include social distancing measures, get a swab test if they have symptoms and wear face covers when necessary, “he added.
The study used fingerstick tests to detect coronavirus antibodies in the blood. When they are present, they indicate that a person has previously been infected with the virus. The test kits, called Lateral Flow Tests, detect antibodies above a particular concentration in the blood and do not measure the amount of antibodies in a particular person.
The findings include the results of three rounds of tests conducted over a three-month period. There were 17,576 positive results in all three rounds, about 30% of which did not report any symptoms.
After taking into account the precision of the test, confirmed by laboratory evaluation, and the characteristics of the population of England, the study found that the prevalence of antibodies decreased from 6.0% to 4.8% and then 4.4% during the three months .
This was found in all ages, but the smallest drop was found in the youngest age group, 18 to 24 years old, going from 7.9% to 6.7% (14.9%), while the oldest decrease was found in the oldest age group, 75 years and over. decreasing from 3.3% to 2.0% (39%).
Helen Ward, one of the lead authors of the research report, said: “This large study has shown that the proportion of people with detectable antibodies is decreasing over time. We do not yet know if this will leave these people at risk of reinfection with the virus that causes Covid-19, but it is essential that everyone follow the guidelines to reduce the risk to themselves and others. “
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