More than 2,500 participants who tested positive in February / March 2020 were tested again in May and November 2020 for antibodies to the virus. Antibody levels were tracked precisely, using 3 tests detecting different types of antibodies that respond to different parts of the virus.
All types of antibodies have gone down with the time since infection,
here, between May and November, however, the analysis finds that:
- 98.8% of people infected in February / March still have detectable levels of antibodies in November;
- no difference in antibody levels was seen between people who had exhibited symptoms of COVID-19 and those who had developed an asymptomatic form
- there are cases of increased antibody levels in some people, suggesting possible re-infections that have boosted the immune system;
- sub-analyzes by outbreak estimate the risk of a person infected with SARS-CoV-2 transmitting the infection to another family member at 25%;
- finally, 79% of transmissions seem to be caused by 20% of infections, which suggests the existence of “ supercontaminateurs »But above all confirms the importance of behavioral factors for controlling the epidemic, and in particular measures such as physical distancing, limiting the number of contacts and wearing a mask.
“These distancing measures continue to be essential in reducing the risk of transmission, even in highly vaccinated populations”, write the authors.
The lead author, Dr. Ilaria Dorigatti of the Imperial, comments on these results: “We found no evidence that the antibody levels between symptomatic and asymptomatic infections differ significantly, suggesting that the strength of the immune response does not depend on the symptoms and the severity of the infection.”
According to the test: antibody levels vary, however, and sometimes markedly, depending on the test used. This means that care should be taken when comparing estimates of infection levels in a population obtained in different parts of the world with different tests and at different times.
With time : the end-of-study evaluation, carried out approximately 9 months later, shows that the antibodies are still less abundant, which suggests the need for monitoring the persistence of the antibodies for longer periods. This result also seems to announce the need for regular or seasonal booster shots.
“It is clear that the epidemic is not over and that it is of fundamental importance to continue administering the first and second doses of the vaccine as well as to strengthen surveillance, including contact tracing.”