Study suggests coronavirus immunity drops after 3 months

The evidence follows several studies published earlier this year from China, the United Kingdom and the USA, which found that people's antibody levels declined sometimes as early as two months after infection. London has maintained the highest prevalence of antibodies across the different rounds, with 9% testing positive in round three, compared with the South West which consistently had the smallest proportion.

The study and university release included suggestions over declining immunity.

Helen Ward, one of the lead authors, said in a statement: "This very large study has shown that the proportion of people with detectable antibodies is falling over time".

Antibodies would be expected to decline over time, as they do with other coronaviruses, like the common cold, but how fast and how far they fall is unknown for Covid-19.

Antibodies are a key part of the body's immune defence and stop viruses from getting inside the body's cells.

Such results have delivered a blow to herd immunity - which, remember, is definitely not the government's real policy of dealing with the virus - due to fears over reinfection once recovery from coronavirus is complete.

Protective antibodies in people who have had Covid-19 wane "quite rapidly", according to researchers.

The research noted a reduction in people's immune response to Covid-19 over time. "If someone tests positive for antibodies, they still need to follow national guidelines including social distancing measures, getting a swab test if they have symptoms and wearing face coverings where required".

"What is not clear is how quickly antibody levels would rise again if a person encounters the Sars-CoV-2 virus a second time". So it isn't unusual to see the prevalence of antibodies drop in the community.

He said healthcare workers were found to have higher levels of antibodies in the study, as did people living in large households and those from black, Asian and minority ethnic backgrounds. "It is possible they will still rapidly respond, and either have a milder illness, or remain protected through immune memory".

The research also raises questions about how long a vaccine would last.

The decline was largest in people who didn't report a history of COVID-19, dropping by nearly two-thirds (64 per cent) between rounds one and three, compared to a decrease of 22.3 per cent in people who had an infection confirmed by lab testing.

The study verifies an observation that other studies have shown, namely, that infection with the coronavirus may not confer "durable immunity", meaning long-lasting immunity, on patients.

Riley also notes this research should not be used to imply vaccine-induced immunity would be short-lived. The researchers say it's still important, as a vaccine might provide better protection than the infection itself. Natural immunity to the novel coronavirus is a complex and murky area, as well.