By NewsDesk  @bactiman63

A study by the Finnish Institute for Health and Welfare (THL) has found that a very large share of people infected with coronavirus in the spring still had detectable antibodies six months later.

The main aim of the study was to find out how long the antibodies last in SARS-CoV2 virus infected persons, and thus also to assess the duration of possible protection. A previous study by THL and the City of Helsinki found that nearly all those infected with coronavirus (63/64) formed antibodies, which also remained for a period of four months in most of the participants.

Persistence of antibodies examined from samples from coronavirus patients

Image by Pete Linforth from Pixabay

The follow-up study for the serological population study of the coronavirus epidemic began in October. People aged 18 or over, who had a coronavirus infection confirmed by PCR-testing in the spring at least six months prior, were invited to take part in the study. The study subjects were selected on the basis of information from the National Infectious Diseases Register. The first blood samples were taken in early November. To date, 1,164 subjects from five different hospital districts have participated in the study.

A microneutralization test developed at THL, was utilized in the antibody study. The microneutralization test measures antibodies that neutralize the virus. Thus far, these antibodies have been found in 792/867 subjects (91%) in the follow-up study.

“The fact that antibodies persist in such a large proportion of those infected for a long time is a promising finding, and, in particular, the persistence of neutralizing antibodies can mean longer-term protection from new infection,” says THL’s Research Manager Merit Melin.

Other recent studies have also shown that neutralizing antibodies persist in a large proportion of those infected, despite a decrease in total antibodies in the months following infection.

The immune response resulting from a coronavirus infection can be influenced by both the characteristics of the virus and the differences between individuals. Coronaviruses that cause severe infections, such as SARS and MERS, can produce antibodies that persist for several years.

The THL study found neutralizing antibodies in all 129 COVID-19 patients who had been hospitalized. Other studies have also shown that patients with severe COVID-19 develop higher levels of antibodies, which also persist longer.


Neutralizing antibodies can protect against infection

The neutralizing antibodies formed in infected persons are likely to provide protection against symptoms or severe symptoms of a new infection, as evidenced by animal experiments. However, it is not yet known which amount of antibodies is sufficient to protect a person from an infection or how long the protection will last.

Neutralizing antibodies target the viral spike protein, on which the majority of vaccines under development are also based. In clinical trials, coronavirus vaccines have produced as good or stronger antibody responses compared to natural infection.

International studies have found that the levels of neutralizing antibodies achieved with new types of mRNA vaccines were high in both young adults and older people. The effectiveness of vaccines has been equally good in people of different ages.

“Our observation that neutralizing antibodies persist in most people for more than six months after infection also increases optimism about the long-term protection provided by vaccines,” says THL’s Research Manager Arto Palmu.

Long-term surveillance of immunity induced by coronavirus infection and by vaccines is important.