Study: Covid-19 antibodies, possible immunity last at least four months

The THL said follow-up research would track possible immunity up to seven months after infection.

The study found that nearly all research subjects developed antibodies within one month of infection. Image: Sami Takkinen / Yle

Coronavirus antibodies remain in the body for at least four months after infection and confer possible immunity from the virus during that time, according to a new Finnish study.

The study looked at 129 people from 39 families in which at least one individual had recently tested positive for Covid-19. Tests were conducted to determine the level of antibodies present that could neutralise the virus in laboratory conditions.

Lead researcher Merit Melin said that the presence of neutralising antibodies in particular suggests possible immunity, although it is not yet known for certain how long it would last.

"The results of the THL study confirm evidence that antibodies created by natural infection and possible immunity would remain for at least four months," Melin said in a statement.

The joint study was conducted by the Finnish Institute for Health and Welfare (THL) and the city of Helsinki.

Antibodies form within one month

The study included a total of 64 people who had lab-confirmed positive coronavirus tests. Researchers identified antibodies in 63 of them.

Another 17 were found to have antibodies although they had not tested positive for the disease.

Nearly all of the Covid-positive research subjects had formed antibodies within the first month after infection.

The quantity of antibodies declined during the monitoring period, but they were present in nearly all subjects four months after infection.

The majority of infected subjects experienced a mild form of the disease and did not require hospitalisation.

Promising results from vaccine standpoint

Previous studies of this nature have yielded inconsistent results about how long antibodies remain in the body. Some studies suggested that antibody counts fell quickly, in some cases in under three months. However more recent research has shown that antibodies remain in the body for longer periods.

The THL said that the results are promising from the perspective of vaccine development.

"Because vaccination also aims to produce long-lasting neutralising antibodies, it is promising that the immunity gained from infection lasts longer than previously reported," THL chief physician Hanna Nohynek said in the statement.

The THL next plans to determine whether or not immunity remains six to seven months after infection. Those results are expected at the end of the year.