Lower vaccine efficacy among weak people against virus variants

The protective efficacy of coronavirus vaccines may be lower for those in frail health than among vaccine recipients on average, according to a study conducted by the Finnish Institute for Health and Welfare (THL).

This applies especially to coronavirus infections caused by virus variants, said the THL in a press release, quoting the study conducted at two nursing homes this spring.

A second vaccine dose is especially important for strengthening the protection.

The study involved testing for antibodies to ascertain what kind of protection can be attained through vaccination against COVID-19, especially against disease caused by virus variants.

The study examined infections caused by variants of the virus in two nursing homes for the elderly. In both, infections were diagnosed among both residents and personnel.

Coronavirus infections caused by the so-called British variant of the virus were diagnosed in a Helsinki nursing home in February this year. All residents of the nursing home and two thirds of the nursing staff had been given one dose of vaccine.

About one in four of the vaccinated residents were infected. Most of the employees who were infected had not been vaccinated.

Coronavirus infections caused by the South African variant were detected in a nursing home in Vantaa, mainly in March. Nearly all residents of the nursing home and half of the personnel were fully vaccinated; they had received two vaccine doses. Half of the personnel had not been vaccinated at all.

In the unit where infections were diagnosed, about half of the residents were infected. Infections were diagnosed among both unvaccinated, and vaccinated residents and among unvaccinated employees.

Symptoms were mild among most of the 15 residents who were infected, and some of the personnel and residents who were infected showed no symptoms. Five of the residents who were infected died. It is not yet certain to what degree the deaths were caused by the coronavirus infection, or to what degree other illnesses may have been involved.

The coronavirus vaccine causes the body to produce antibodies which recognise the virus and can later protect against infection and serious disease. Already after one dose of vaccine, all nursing home employees and nearly all residents had antibodies against the coronavirus. As expected, those who had received two doses of vaccine had higher levels of antibodies.

However, residents had significantly fewer antibodies than personnel did. After the first vaccine dose most residents and a few members of staff had no measurable amount of so-called neutralising antibodies, which probably play the biggest role in developing the protection. The level of neutralising antibodies was especially low against virus variants, and especially against the South African mutation.

“The likely reason is that some variants of the virus are capable of dodging the protection given by the vaccines. This seems to be the case especially among frail and elderly people with a lower level of antibodies”, said Merit Melin, Research Manager at THL.

However, after two vaccine doses, neutralising antibodies were detected among all of those who were studied.

“This means that getting a second vaccine dose is very important to ensure that the vaccine gives optimal protection against both the original virus and virus variants”, Melin said.

“Monitoring virus variants and developing vaccines against the variants must be continued, as some of the variants can avert the protection afforded by vaccines more effectively than others. Even after two vaccine doses, neutralising antibodies against the South African variant were detected only from one of the residents. This does not mean that there would be no protective efficacy; in addition to the antibodies, it is likely that so-called cell-mediated immunity helps the body to defend against serious disease.”

The so-called Indian variant of the virus was not found in the nursing homes that were studied, but it has been detected more frequently in Finland in recent weeks.

“According to a recently published study in the U.K., the efficacy of coronavirus vaccines against the Indian variant is weakened, but less than with the South African variant. After a second vaccine dose, the effectiveness of both the Biontech-Pfizer and the AstraZeneca vaccines against the Indian variant was about 34 percent. This means that infections are to be expected after the first dose of the vaccine”, said THL Chief Physician Hanna Nohynek.

The lower efficacy of the AstraZeneca coronavirus vaccine could be partially attributable to the fact that more elderly people were among those getting the vaccine, and that the monitoring period in the study after the second dose was shorter than it was with the Biontech-Pfizer vaccine. The efficacy of vaccines is often lower with the elderly than it is among the young.