COVID-19 Antibodies Last at Least 9 Months After Infection

New research indicates that COVID-19 antibodies persist for at least nine months after infection.

Tests from an entire Italian city show that antibody levels remain high, whether symptomatic or asymptomatic, nine months after SARS-CoV-2 infection.

Researchers from the University of Padua and Imperial College London tested more than 85 percent of the 3,000 residents of Vo’, Italy, for infection with SARS-CoV-2, the virus that causes COVID-19, in February/March 2020. she tested. again in May and November 2020 for antibodies to the virus.

The team found that 98.8 percent of people infected in February/March had detectable levels of antibodies in November, and there was no difference between people who had symptoms of COVID-19 and those who had no symptoms. The results will be published today (July 19, 2021) in Nature Communications.

A researcher who tests a child as part of the study. Credit: Andrea Crisanti

Antibody levels were monitored using three ‘assays’ – tests that detect different types of antibodies that react to different parts of the virus. The results showed that while all antibody types showed some decline between May and November, the degree of decay was different depending on the test.

The team also found cases of elevated antibody levels in some people, indicating possible re-infections with the virus, which boosts the immune system.

Lead author Dr. Ilaria Dorigatti, of the MRC Center for Global Infectious Disease Analysis and the Abdul Latif Jameel Institute for Disease and Emergency Analytics (J-IDEA) at Imperial, said: “We found no evidence that antibody levels between symptomatic and asymptomatic infections differ significantly, which suggests that the strength of the immune response does not depend on the symptoms and severity of the infection.

“However, our research shows that antibody levels vary, sometimes significantly, depending on the test used. This means that caution should be exercised when comparing estimates of infection levels in a population obtained in different parts of the world with different tests and at different times.”

Professor Enrico Lavezzo, from the University of Padua, said: “The tests in May showed that 3.5 percent of the Vo’ population had been exposed to the virus, although not all of these subjects were aware of their exposure given the large fraction of asymptomatic infections.

“However, at the follow-up, which was done about nine months after the outbreak, we found that antibodies were less abundant, so we need to continue monitoring the persistence of antibodies for a longer period of time.”

The team also examined the infection status of household members to estimate how likely an infected member is to pass the infection on within the household. Their modeling suggests that there was about a 1 in 4 chance that a person infected with SARS-CoV-2 will pass the infection on to a family member, and that most transmission (79 percent) is caused by 20 percent of infections.

This finding confirms that there are large differences in the number of secondary cases generated by infected people, with most infections causing no further infections and a minority of infections causing a large number of infections.

The large differences in how an infected person can infect others in the population suggests that behavioral factors are key to epidemic control, and physical distancing, as well as limiting contact and wearing masks, remain important to reduce the risk of transmission. reduce disease, even in highly vaccinated populations.

The team’s dataset, which includes the results of the two mass PCR testing campaigns conducted in February and March and the antibody studies conducted in May and then in November, also allowed them to discern the impact of different control measures. .

They showed that manual contact tracing alone would not have been enough to suppress the epidemic in the absence of isolation and short lockdowns.

Project leader Professor Andrea Crisanti, from Imperial’s Department of Life Sciences and Department of Molecular Medicine at the University of Padua, said: “Our study also shows that manual contact tracing – the search for positive individuals based on known and declared contacts – would have had a limited impact on the containment of the epidemic had it not been for massive screening.”

dr. Dorigatti added: “It is clear that the epidemic is not over, neither in Italy nor abroad. Going forward, I think it is fundamental to continue administering first and second vaccine doses and to strengthen surveillance, including contact tracing. Encouraging caution and limiting the risk of contracting SARS-CoV-2 remains essential.”

Reference: July 19, 2021, Nature Communications.
DOI: 10.1038/s41467-021-24622-7