In two-thirds of the studied nursing home residents, the number of virus-neutralizing antibodies decreased by more than 80 % after six months of vaccination.

Six months after vaccination with a drug from Pfizer, less than a third of the elderly people studied retained full-fledged immunity to a new type of coronavirus. Scientists from the United States reached this conclusion; the results of their study are published on medRxiv.

“In six months, the number of antibodies capable of combining and neutralizing coronavirus particles in all groups of volunteers fell by more than 80%. As a result, six months after vaccination, 72% of nursing home residents had no or almost no antibodies,” the researchers write.

Doctors do not yet have a clear answer to the question of whether vaccines or a previous coronavirus infection can cause long-term immunity to existing and new strains of SARS-CoV-2. Observations of recent months show that in some cases, antibodies to the virus disappear within 6-8 months after the disease, while in other cases, immunity persists much longer.

Such results force doctors and biologists to study even more actively how exactly antibodies disappear from the body of those who have been ill and how this process affects the body’s resistance to the action of coronavirus. In addition, scientists are trying to understand whether there are differences in this regard between different COVID-19 vaccines.

In a new study, doctors led by Professor David Canaday of Case Western Reserve University (USA) tried to find out how quickly the concentration of antibodies in the body of the most vulnerable people to COVID-19-residents of nursing homes and their nurses-decreases.

This study involved 120 Americans with an average age of about 76 years and 92 medical professionals who reached the fourth or fifth decade of life. All of them received two doses of the vaccine from Pfizer earlier this year.

Scientists collected blood samples from all of them two weeks after vaccination and determined the level of antibodies. The researchers conducted similar tests six months after the first study. A comparison of these data showed that the effectiveness of the vaccine in nursing home residents was significantly lower than the average in the United States.

In particular, this was manifested because the concentration of antibodies in their bloodstream was initially low – they were present in the body of only 84% of elderly patients. After six months, this indicator decreased by another 80%, resulting in which antibodies were absent or observed in minimal amounts in 72% of residents of nursing homes.

This was not observed among medical professionals and those elderly people who had suffered COVID-19 before vaccination. Only 9% of such volunteers lost immunity to the coronavirus six months after vaccination.

According to Canaday and his colleagues, such observation results indicate the need for regular and frequent re-vaccination of the elderly. This became especially important after the penetration of the delta strain into the United States, the researchers concluded.