Herpesviruses, including the pathogen that causes chickenpox, have long been suspected of being associated with dementia. The new results support this hypothesis.
Vaccination against shingles appears to reduce the risk of dementia. This is the conclusion reached by a working group led by Markus Eyting from the Heidelberg Institute of Global Health based on data from unvaccinated people in Wales and those vaccinated with the live vaccine Zostavax. As the team reports in a preliminary publication, people in a group with a vaccination rate of around 50 percent were one-fifth less likely to develop dementia than an almost completely unvaccinated comparison group. The result supports the hypothesis that the chickenpox virus, which causes shingles, is involved in the development of dementia.
Study confirms suspicion
Dementia is a growing problem worldwide and to date there is no effective therapy for mental loss. For some time, however, there has been a suspicion that infectious diseases could be involved in some dementia diseases. Several studies have provided evidence that herpesviruses, particularly HSV-1 and the chickenpox virus, are associated with a higher risk of dementia. These viruses infect nerve cells and in some cases can cause encephalitis. They also appear to damage the brain in subtle ways, contributing to Alzheimer’s and other neurodegenerative diseases.
Shingles as a late consequence of chickenpox
Shingles is a late effect of chickenpox infection, in which the virus becomes active again and causes a painful rash. The Zostavax vaccine cuts the incidence of shingles by about half. In Wales, the vaccine is only offered to people born after September 2, 1933. This cut-off date allowed the working group to carry out its analysis. In the study, the team compared people who were born in the week before the deadline with those whose birthday falls in the week after. In the latter, the vaccination rate was 47 percent, in the former almost zero.
The study does not directly compare the vaccinated with the unvaccinated. However, the working group argues that in this way differences between them, which are difficult to reliably determine, do not skew the result. A higher willingness to vaccinate could be associated with higher education and possibly a lower risk of dementia. On the other hand, the two groups examined in this study are easily comparable: there is no plausible reason why it should make a systematic difference whether someone was born in the week before or after September 2, 1933.
Greater protection in women
According to the team’s analysis, dementia occurred about 20 percent more often in the unvaccinated group than in the group with a 47 percent vaccination rate over the seven-year period examined. The data also show that the protective effect is stronger in women than in men. This could be due to differences in the immune system or that the chickenpox virus causes a higher proportion of dementia cases in women. The publication has not yet been independently checked, and the result has yet to be verified in further studies. However, the finding is not unexpected and fits in with the results of previous studies and the general state of research on neurodegenerative diseases and herpes viruses.