THL study: coronavirus vaccine protects the elderly and those in the risk group much better after the second injection
A study by the Finnish Institute for Health and Welfare (THL) shows that a second dose of a coronavirus vaccine is essential to give the elderly and those in the medical risk group sufficient protection against coronavirus disease. The protection provided by a single dose is significant, but it does not always prevent infection, and in some cases, it will not prevent a case of coronavirus disease that requires hospital care.
The study was conducted using medical and demographic register data from Finland. The study examined the protective effect of the first and second doses of a vaccine against coronavirus infections and cases of coronavirus disease that require hospitalisation. The results of the study are preliminary, and they have not yet been subjected to scientific peer-review.
Second dose provides excellent protection against severe disease
For the elderly, the protective effect of mRNA vaccines against coronavirus infection was on average 45 percent, i.e. about 45 out of 100 coronavirus infections were prevented by the first injection. The effectiveness of the first dose was 63 percent against coronavirus disease requiring hospital care. For those in the risk group, the results were 40 percent against infection and 82 percent against hospitalisation. The protective effects were calculated at the earliest three weeks after the first dose.
“After the first dose of the vaccine it is still possible to be infected and get ill. Coronavirus vaccines provide better protection against severe disease than against mild infections in the same way that seasonal flu shots do”, says Eero Poukka, Medical Specialist at THL.
Among the elderly, the protective effect of mRNA vaccines against infection increased to 75 percent after the second dose and to 93 percent against hospitalisation. In the risk group, the corresponding figures were 77 and 90 percent.
“These figures clearly indicate that a second dose of the coronavirus vaccine is worth taking. A second dose increases the protective effect to excellent levels both among the elderly and those in the risk group”, Poukka says.
Protective effect of adenovirus vector vaccine is similar to that of mRNA vaccines
The protective effect of the AstraZeneca adenovirus vector vaccine against infection three or more weeks after the first dose was 42 percent among those in the risk group, and 62 percent against hospitalisation.
“When we consider the fairly large confidence intervals of our estimates, we did not find meaningful differences between the effectiveness of mRNA and adenovirus vector vaccines. Similar results have been obtained previously in studies conducted in the UK”, says THL statistician Ulrike Baum.
During the study, only a few were vaccinated with the second dose of the AstraZeneca vaccine and the number of adenovirus vector vaccine doses given to the elderly was small. Consequently, data derived from them could not yet be utilised in the analysis. As the vaccination campaign goes on, THL is continuing to analyse the protective effect of the coronavirus vaccines, aiming for a more extensive evaluation of the effectiveness of adenovirus vector vaccines in the future.
The coronavirus vaccine effectiveness is also being monitored in younger age groups. According to results from other countries, coronavirus vaccines are on average more effective among those under 70 years of age than those who are older. In addition to age and underlying comorbidities, study results on vaccine effectiveness also depend on the virus variants that are circulating in the population during the study.
The research includes information on nearly 1.7 million recipients of the vaccine
The study was conducted between 27 December 2020 and 24 May 2021 using medical and demographic register data. More than 900,000 elderly persons and 775,000 persons at risk for severe coronavirus disease were followed up for their coronavirus vaccinations, infections, and related hospitalisations. The utilised register data did not include personal information that could reveal the identity of any individual person.
Of the elderly – those who are at least 70 years of age – 89 percent had received at least one dose of a coronavirus vaccine. Those in the risk group were 16–69 years of age and 69 percent of them were vaccinated at least once. With minor exceptions, the risk groups in this study were the same as those that determined the coronavirus vaccination order.
Vaccination order for risk groups
Further information:
Ulrike Baum
THL
Statistician
[email protected]
Eero Poukka
THL
Medical Specialist
[email protected]
