Antibody levels remain high nine months after a SARS-CoV-2 or Covid-19 infection, whether symptomatic or asymptomatic, a new study based on testing an entire Italian town concludes on Monday.
Researchers from the University of Padua in Italy and Imperial College London tested more than 85 per cent of the 3,000 residents of Vo’, a commune in Italy, in February-March 2020 for infection with SARS-CoV-2, the virus that causes Covid-19, and tested them again in May and November 2020 for antibodies against the virus. The team, which has published its findings in the ‘Nature Communications’ journal, found that 98.8 per cent of people infected in February-March showed detectable levels of antibodies in November, and there was no difference between people who had suffered symptoms of and those that had been symptom-free.
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“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,” said Lead Author Dr Ilaria Dorigatti, from the MRC Centre for Global Infectious Disease Analysis and Abdul Latif Jameel Institute for Disease and Emergency Analytics at Imperial College London.
“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,” she said.
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 increasing in some people, suggesting potential re-infections with the virus, providing a boost to the immune system.
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Professor Enrico Lavezzo, from the of Padua, said: “The May testing demonstrated that 3.5 per cent of the Vo’ population had been exposed to the virus, even though not all of these subjects were aware of their exposure given the large fraction of asymptomatic infections.
“However, at the follow-up, which was performed roughly nine months after the outbreak, we found that antibodies were less abundant, so we need to continue to monitor antibody persistence for longer time spans.”