Register study: Variant-tailored coronavirus vaccines have reduced the number of severe cases among people over 65 years of age
Variant-tailored coronavirus vaccines have provided additional protection against severe coronavirus disease for people over 65 years of age in Finland. According to preliminary analyses, protection seems to decrease slightly a few months after vaccination. Despite the decrease in the effectiveness of the protection, the risk of severe coronavirus disease remains relatively low for those who have been vaccinated.
This is revealed in a register study examining the protection provided by variant-tailored coronavirus vaccines for people aged 65 or over and persons aged 18 to 64 belonging to risk groups in Finland. In the analysis, recipients of a variant-tailored vaccine were compared to people of the same age who had received at least two doses of the original vaccine before 1 September 2022 and whose latest vaccine dose or laboratory-confirmed case of the coronavirus disease had been at least three months earlier.
The analysis included about 1,200,000 older persons and about 445,000 persons belonging to risk groups. The monitoring period was from 1 September 2022 to 31 January 2023.
During the five-month monitoring period, the number of cases requiring hospitalisation among the group of over 65-year-olds included in the analysis was 1,721. In the monitored group of over 65-year-olds, the coronavirus caused 1,002 deaths and contributed to 809 deaths. The number of cases of coronavirus disease requiring hospitalisation among persons belonging to risk groups included in the analysis was 240. Among the persons belonging to risk groups, the coronavirus disease caused 16 deaths and contributed to 18 deaths.
"Compared to the early days of the pandemic, the risk of severe coronavirus disease among older persons and those belonging to risk groups has decreased considerably. At the end of last year, the increase in the number of severe cases was related to the large overall number of infections," explains Eero Poukka, Medical Specialist at Finnish National Institute for Health and Welfare (THL).
More research evidence needed on the effectiveness of variant-tailored vaccines
Based on the analysis, the additional benefit provided by variant-tailored vaccines seemed to decrease after two months.
"However, the relative decrease in the protective effect of variant-tailored vaccines does not mean that the risk of severe coronavirus disease would be significant after two months," Poukka explains.
In the interpretation of the results, it is essential to take into account that the control group consisted of previously vaccinated persons, some of whom had also had the coronavirus disease. For this reason, the risk of severe coronavirus disease was relatively low even among those in the control group.
"We still have very little research literature on the duration of the protective effect of variant-tailored vaccines. Before the final conclusions, the analysis should be repeated with a longer monitoring period and with other study designs,” Poukka continues.
People belonging to risk groups had relatively few cases of severe coronavirus disease
In the analysis, the 18 to 64-year-olds belonging to risk groups had few severe cases of coronavirus disease.
In this group, those who received a variant-tailored vaccine had the same risk of developing a severe case of the coronavirus disease as those who did not get a variant-tailored vaccine, i.e. the vaccine did not seem to provide any additional benefits. However, this observation might be biased.
"The persons whose coronavirus disease has been confirmed with home testing cannot be identified on the basis of national registers. These persons were likely to apply for a variant-tailored vaccine more rarely. However, they had hybrid immunity from getting the previous vaccines and having had the disease, and it provides excellent protection against severe coronavirus disease. This may explain why those who received a variant-tailored vaccine were not found to have a lower risk of severe coronavirus disease than the control group that had not applied for the variant-tailored vaccine," explains THL Statistical Researcher Ulrike Baum.
THL continues to monitor the effectiveness of vaccines and the epidemic
The epidemic situation in Finland is calm at the moment, and there is most likely no reason to expect any major epidemic surges in the spring similar to last year.
"In Finland, there is currently no need for extensive booster vaccinations at the population level, as there are few coronavirus infections at the moment. From the perspective of society, vaccinations at the population level require a lot of resources, and when considering extensive vaccinations, it is important to assess the relationship between the required resources and effectiveness,” says Eero Poukka.
THL will continue to monitor the effectiveness of the vaccines and the development of the epidemic.
"Almost real-time register data is utilised in the analysis," Baum points out.
Further information
Getting vaccinated against COVID-19
Eero Poukka
Medical Specialist
THL
[email protected]
Ulrike Baum
Statistical Researcher
THL
[email protected]
