THL study: antibodies from coronavirus disease still present a year after the illness

Note! This press release was first published in Finnish on the 22nd of July

A study by the Finnish Institute of Health and Welfare (THL) has shown that neutralising antibodies were present in most former coronavirus patients a year after the infection. The fresh study examined the preservation of antibodies produced by coronavirus disease in people both six months and a year after being infected.

As many as 97 percent of those examined were found to have the IgG antibody, which recognises the spike protein of the coronavirus, a year after the infection. Although antibodies were detected in many former patients, the amount was one third lower than it had been six months after the infection.

“Studying the antibody levels after a case of coronavirus disease gives important information that also helps in evaluating the protection offered by vaccines, and the duration of the protection”, says Merit Melin, Research Manager at THL.

Those taking part in the study had coronavirus disease in the spring of 2020

People invited to take part in the study had been infected by coronavirus in the spring of 2020. The infection was confirmed by a PCR test, after which they had no new coronavirus infections, and had not received a coronavirus vaccine before the samples were taken.

A total of 1292 people were examined six months after the infection and 367 were checked after a year. Of those examined after six months, 15 percent had been stricken by a serious coronavirus infection requiring hospitalisation. Of those examined after a year, the figure was 13 percent.

Those who had suffered a severe case of the disease requiring hospitalisation had a significantly higher antibody level than those with a mild case. All those who suffered a severe case of the disease had neutralising antibodies a year later.

“The results of the study indicate that after an infection of the coronavirus, the neutralising antibodies and the protection against a new infection last for a long time if the level of antibodies was high from the outset”, Melin says.

Antibody level lower against virus variants

The study also examined the ability of the antibodies to neutralise mutated forms of the virus. The level of neutralising antibodies against the Alpha variant was slightly lower than with the original form, and significantly lower against the Beta and Delta variants. The antibody levels had declined significantly among those with a mild form of the disease.

Infections caused by virus mutations have also been diagnosed among those who have been vaccinated, both after a single dose and two doses of the vaccine. However, the vaccines give good protection against serious forms of the disease caused by variants of the virus.

“Protection that comes as a result of an infection or vaccination is based both on antibodies and cell-based immunity, as well as memory cells which are activated and produce antibodies when they confront the cause of the disease”, Melin explains.

Persistence of neutralizing antibodies a year after SARS-CoV-2 infection

More information

THL, Communications
tel. 029 526 6161, mon-fri at 9-16
[email protected]