Covid-19 antibodies last for at least nine months after infection, new study finds

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  • A new study found that people still have Covid-19 antibodies nine months after infection.
  • Being symptomatic or asymptomatic did not make any difference.
  • The study observed 86% of households in an Italian town.

A new study has found that antibody levels remain high nine months after SARS-CoV-2 infection, regardless of whether people were symptomatic or asymptomatic.

The research published in Nature Communications assessed the antibody levels of residents of a town in Italy after they were tested during the first wave of Covid-19 infections.

Testing a town

The researchers from the University of Padua and Imperial College London tested almost all of the 3 000 residents of Vo', Italy, in February and March 2020 for infection with SARS-CoV-2, the virus that causes Covid-19. They tested them again in May.

Then, in November 2020,  the researchers collected blood samples of the people diagnosed with Covid-19, and tested for virus antibodies.

The study authors also investigated the individual infection status of household members to estimate the likelihood of cross-infection within a household.

Long-lasting antibodies

The study's findings show that  98.8% of people infected in February and March showed detectable levels of antibodies in November. There was no difference between people who had Covid-19 symptoms and those who had been asymptomatic.

"We found no evidence that 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," says lead author Dr Ilaria Dorigatti in a press statement.

"However, our study does show that antibody levels vary, sometimes markedly, depending on the test used. This means that caution is needed when comparing estimates of infection levels in a population obtained in different parts of the world with different tests and at different times," says Dorigatti.

The researchers also found that antibody levels increased in some people. This suggests a potential re-infection of the virus that gave a boost to the immune system.

The epidemic isn't over

The study results also show a probability that one in four people infected with SARS-CoV-2 passed the infection on to a family member.

According to the study authors, case isolation, short lockdowns and manual contact tracing alone would not have been enough to suppress the epidemic. Vaccination is vital to combat the virus.

"It is clear that the epidemic is not over, neither in Italy nor abroad. Moving forward, I think that it is of fundamental importance to continue administering first and second vaccine doses as well as to strengthen surveillance, including contact tracing. Encouraging caution and limiting the risk of acquiring SARS-CoV-2 will continue to be essential," says Dorigatti.

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