Elderly with few antibodies may need an extra dose of vaccine

Linnea Vikström, doktorand vid Institutionen för klinisk mikrobiologi

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“The result suggests that we should be able to identify in advance which people have the greatest risk of being seriously affected and may need extra efforts in the form of, for example, additional vaccine doses”, says Linnea Vikström, PhD student at the Department of Clinical Microbiology at Umeå University and joint first author of the study.

Starting in September 2021, the researchers have followed 114 different special housing units with a total of just over 3,000 people in Skåne, Stockholm, Örebro, Jämtland-Härjedalen and Västerbotten Counties. Finger prick blood samples have been taken every three months from the residents and compared with data on illness and death. The average age in special housing for the elderly is 86 years.

96-fold increase

By October 2021, almost all residents had received the third dose of the covid vaccine. The researchers could then see a 96-fold increase in the amount of antibodies in the blood. The fourth dose in March 2022 only gave a fourfold increase in the antibodies, which can be explained by the fact that the level was already high then. The researchers were also able to establish that the amount of antibodies was largely the same for people over and under 65 years of age. This suggests that the mRNA vaccines given in doses three and four worked just as well for the elderly as for the younger.

The researchers continued with studies on a smaller group of how vaccination protects against the different omicron variants of COVID-19. With supplementary blood samples, the ability of the antibodies to neutralize the virus variants was analysed. It was then possible to see that the antibodies did not protect against contracting the disease in themselves. In contrast, the antibodies greatly reduced the risk of dying from the disease.

Higher mortality

People with lower levels of antibodies had increased mortality within 30 days of infection. When the researchers performed statistical analyses on test results of all the elderly who participated in the study, they saw that the people with the ten percent lowest levels of antibodies in their blood were three to four times as likely to die within 30 days of being diagnosed with the virus.

The lower level of antibodies in some elderly people is probably related to the fact that there may be individual differences in how different people's immune systems react to vaccines.

“The study can help us and other researchers understand how the different variants of the virus get past the immune system among the elderly and how the vaccine needs to be developed to protect against serious illness and death”, says Linnea Vikström.

The research will continue in 2023. It is supported by the Swedish Public Health Agency, Vinnova and Scilifelab via the Knut and Alice Wallenberg Foundation. The study is published in the scientific journal The Lancet Regional Health – Europe.