A group of Swedish scientists working under the leadership of Charlotte Thalin from the Karolinska Institute in Uppsala decided to find out how long and how effectively the immune system protects people who have had coronavirus and people vaccinated against covid. Patients from Danderyd Hospital in Stockholm were selected as "test subjects".
The scientists published their findings as a preprint in the electronic library medRxiv. Let's make a reservation right away that the preprint is not a full-fledged scientific article, so it did not pass the verification of third-party experts.
According to the authors of the publication, after suffering a mild SARS-CoV-2 infection, patients experience an initial decrease in the level of IgG antibodies to SARS-CoV-2. This antibody level then remains stable for 12 months. These antibodies effectively neutralize both the "wild" strains of SARS-CoV-2 and the subsequently emerging "alpha" and "delta" strains, which indicates the formation of stable immunity to them. It is noteworthy that the neutralizing ability of antibodies is significantly reduced in relation to strains "beta" and "gamma".
Doctors conducted their experiment on a hundred volunteers who had recovered from COVID-19 with mild symptoms, without hospitalization, in the middle of spring 2020.
All study participants had a blood test every four months, which allowed the researchers to compare how the ability of their immunity to resist the "wild" and mutated strains of SARS-CoV-2 changed.
The results of the experiment showed that the number of antibodies in the blood serum of those who had recovered significantly decreased over the year of observation. However, antibodies have not lost their ability to effectively neutralize the coronavirus. This applied to both the original SARS-CoV-2 strain and its British ("alpha") and Indian ("delta") mutations. But with the Brazilian ("gamma") and South African ("beta") strains of the virus, antibodies coped worse, both immediately after the illness and within 12 months after it.
A similar picture was observed in the study of antibodies of groups of volunteers vaccinated against coronavirus with vaccines from Pfizer and AstraZeneca. There were three such groups. The first received two shots of Pfizer, the second two shots of AstraZeneca. The third group received the AstraZeneca vaccine at the first shot and Pfizer on the second shot.
According to the researchers, the same effectiveness of antibodies in those who have been ill and vaccinated suggests that both the transferred infection and vaccinations contribute to the development of stable immunity to the "wild" version of COVID-19, and to its alpha and delta mutations.
But to combat the strains "beta" and "gamma", scientists, apparently, will have to look for additional weapons. New data will need to be used in the development of a new generation of vaccines, Swedish scientists emphasize.