Study: BA.1 or BA.4–5 bivalent Covid-19 vaccines decreased disease severity in the elderly population
According to a recent Nordic study, bivalent BA.1 and BA.4–5 Covid-19 vaccines reduced the number of severe Covid-19 cases in the elderly population.
The elderly are at high risk of severe Covid-19 requiring hospitalisation, which is why a fourth dose of the Covid-19 vaccine has been recommended for them. A study conducted in Finland, Sweden, Norway and Denmark compared elderly people who had received a bivalent vaccine as a fourth dose to those who had received only three doses of a monovalent (original) Covid-19 vaccine. Of the bivalent vaccines, the BA.4–5 vaccine reduced the number of Covid-19 cases requiring hospitalisation among the elderly by 80.5% (95% confidence interval 69.5–91.5%) and the BA.1 bivalent vaccine by 74% (68.6–79.4%).
“The research results are in line with the results from the United States, Israel and the United Kingdom. Bivalent vaccines provide good protection against severe disease when they are given as a booster to those who have received three doses of a monovalent vaccine," says Eero Poukka, Medical Specialist at THL.
The study also compared the protection of persons who were vaccinated with four monovalent doses to those who were vaccinated with three such doses. The fourth dose reduced the number of Covid-19 cases requiring hospitalisation among elderly people by 64.9% (57.7–72.2%).
The study population consisted of persons aged 50 to 65 years and older. The age range varied by country depending on the age groups for which four vaccine doses had been recommended. In Finland, the study population included persons aged 60 years or more. During the study, the BA.5 virus variant was the dominant SARS-CoV-2 strain.
Slight differences in the protection of bivalent vaccines among the elderly – further research is needed
The study also compared BA.1 or BA.4–5 bivalent vaccines. Those who were vaccinated with the BA.4–5 vaccine as fourth dose had a 32.3% (10.6–53.9%) lower risk of Covid-19 requiring hospitalisation than those who received the BA.1 vaccine as their fourth dose. This result is mainly based on data from Denmark.
“The protection of both bivalent vaccines against severe disease is good, but it is possible that the BA.4–5 vaccine provided slightly better protection against Covid-19 caused by the BA.5 virus variant. However, the study should be repeated elsewhere, or in the Nordic countries, but with a longer follow-up period. This would give a better picture of whether there is a real difference in vaccine effectiveness,” says THL's Statistical Researcher Ulrike Baum.
The difference in the protective effect of the bivalent vaccines may be explained by the fact that BA.5 was the dominant variant during the study. The virus is constantly mutating; and with the emergence of new virus variants, there will likely be no difference in the effectiveness of these bivalent vaccines. Furthermore, it should be noted that the difference in effectiveness between the bivalent vaccines is small.
“More important than which vaccine product has been used is that the elderly and others in risk groups receive their boosters as recommended,” says Poukka.
Further information
Vaccines and coronavirus (THL)
Eero Poukka
Medical Specialist
THL
tel. +358 29 524 7956
[email protected]
Ulrike Baum
Statistician
THL
tel. +358 29 524 7504
[email protected]
