THL for 5th vaccine dose for severely immunodeficient

The Finnish Institute for Health and Welfare (THL) recommends new booster doses for those aged 12 or over whose immune system is severely weakened.

The new booster dose means a fifth dose of the coronavirus vaccine, said the THL in a press release on Friday.

Severely immunocompromised people have either a congenital immunodeficiency, an illness or medication that affects their immune response and significantly weakens their response to the vaccine. This group consist of about 10,000 to 30,000 people.

Fourth vaccine doses were recommended for those with severe immunodeficiencies as early as December 2021.

For them, the fourth vaccine dose was considered to be a booster equivalent to that of the third dose administered to the rest of the population. Previous studies have shown that booster doses can improve the vaccine response in severely immunodeficient people.

According to the preliminary research results of THL, the amount of antibodies in severely immunodeficient people after the fourth vaccine dose is on average one third of the vaccine response of healthy adults after three doses. Vaccine responses of severely immunodeficient people vary, as the severity of the immunodeficiency affects the level of the response.

Persons aged 18 or over, who had received the fourth coronavirus vaccine dose after the recommendation for those with severe immune deficiencies was issued on 22 December 2021, were invited to THL’s study.

The antibody levels of 433 subjects were measured about one month after the fourth dose.

Vaccine responses of severely immunodeficient people were compared with responses in healthy adults who had received the third vaccine dose about one month before the sample was taken.

According to a previous study by THL, the third vaccine dose produced Omicron neutralising antibodies in all healthy adults examined. On average, three out of four (76%) of those with severe immunodeficiency were measured to have Omicron BA.2 variant neutralising antibodies one month after the fourth dose.

The number of antibodies decreases in the months following vaccination. Protection against the coronavirus infection also decreases rapidly after the latest vaccine dose.

However, protection against serious disease is based not only on antibodies but also on memory cells and cell-mediated immunity, which function in healthy persons for a long time.

Although three doses of the vaccine are likely to provide long-term protection against severe coronavirus disease in healthy adults, the risk of serious disease is particularly high for those with severe immune deficiencies.

The booster dose can be administered four to six months after the fourth dose. The coronavirus infection also corresponds to one vaccine dose for those with immunodeficiencies, so a person who has had the disease and has received four vaccine doses does not need a fifth vaccine dose at this stage.

THL's recommendation is based on a joint assessment by the National Advisory Committee on Vaccines (KRAR) and the National Institute for Health and Welfare.