COVID-19 antibodies persist at least nine months after infection, study finds

Andrea Crisanti

Antibody levels remain high nine months after infection with SARS-CoV-2, the virus that causes the novel coronavirus (COVID-19), whether symptomatic or asymptomatic, according to a new study published in the journal Nature Communications.

For the study, researchers from the University of Padua and Imperial College London tested more than 85 percent of the 3,000 residents of Vo', Italy in February and March 2020 for infection with SARS-CoV-2, and tested them again in May and November 2020 for antibodies against the virus.

The team found that 98.8 percent of people infected in February and March showed detectable levels of antibodies in November, and there was no difference between people who had suffered symptoms of COVID-19 and those that had been symptom-free. 

Antibody levels were tracked using three assays, tests that detect different types of antibodies that respond to different parts of the virus. The results showed that while all antibody types showed some decline between May and November, the rate of decay was different depending on the assay. The team also found cases of antibody levels increasing in some people, suggesting potential reinfections with the virus, providing a boost to the immune system.

Additionally, the team investigated the infection status of household members, to estimate how likely an infected member is to pass on the infection within the household. Their modelling suggests that there was a probability of about 1 in 4 that a person infected with SARS-CoV-2 passes the infection 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 generating no further infections and a minority of the infections generating a large number of infections.

The large differences in how one infected person may infect others in the population suggests, researchers said, that behavioral factors are key for epidemic control, and physical distancing, as well as limiting the number of contacts and mask wearing, continue to be important to reduce the risk of transmitting the disease, even in highly vaccinated populations.

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