HPV vaccination does not affect the risk of hospitalisation for infectious diseases in Denmark

Disease and treatment 12. okt 2021 2 min Senior Researcher, Professor Anders Peter Hviid Written by Kristian Sjøgren

Some researchers have been concerned that human papillomavirus (HPV) vaccination may increase the susceptibility of girls and women to non-targeted infectious diseases – but research in Denmark refutes this.

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Tens of thousands of girls and women in Denmark are HPV vaccinated each year to avoid becoming infected later in life with HPV, which can lead to cancer in the worst case.

However, some researchers have claimed that vaccination with types of vaccines such as HPV may increase susceptibility to non-targeted infections. Naturally, the worst-case scenario would be if vaccination against one virus increases the risk of being infected by another type.

However, a new study in Denmark refutes these concerns.

The researchers reviewed registry data for 853,879 girls and women born in Denmark, and the result was clear: HPV vaccination did not increase the risk of being hospitalised with another type of infection.

“Because both researchers and social media have raised concerns, achieving clear results from a large study is important. We have now done this, and our extensive data set provides no evidence that HPV vaccination increases the risk of developing other infectious diseases. In fact, the data show slightly fewer hospital admissions than expected after HPV vaccination,” explains the lead researcher behind the study, Anders Hviid, Professor and Senior Researcher, Department of Epidemiology Research, Statens Serum Institut, Copenhagen.

The research has been published in The Lancet Regional Health Europe.

Some vaccinations may affect the general immune response

Several research projects have raised concerns that some vaccinations may alter the risk of becoming infected with viruses or bacteria other than those they are designed to combat.

Some of these projects have indicated that vaccination with non-live vaccines leads to increased mortality from other non-targeted infectious diseases. However, most of the available evidence is from observational studies in western Africa, primarily among young girls.

Conversely, other studies, including registry research in Denmark, have shown that vaccination with some live vaccines such as the smallpox vaccine actually provide protection that extends beyond the viruses the vaccine is designed to help the immune system recognize.

“The idea was not plucked from thin air, but we do not know anything about how long the effect lasts or whether it is clinically relevant at all. But since concerns have been raised, we should examine whether there is an association. This is especially true because today we produce more and more non-live vaccines, including for HPV and COVID-19. So naturally it is worrying if modern vaccines turn out to weaken the immune system. We therefore sought any signs that this might be true,” says Anders Hviid.

Examined data on more than 850,000 girls and women in Denmark

Anders Hviid and a colleague combed Denmark’s comprehensive health registries, which enable researchers to search for health information on all residents.

They included 853,879 girls and women born in Denmark and 10–29 years old during 2007–2016. They then used the Danish National Patient Registry to identify those who had been hospitalised with an infectious disease.

The researchers compared the risk of this hospitalisation among the vaccinated women and girls versus the unvaccinated women and girls in the 3 months after vaccination.

The researchers identified 65,293 hospitalisations for infectious diseases among 50,599 women and girls, including 46,955 cases among 37,003 vaccinated women and girls.

HPV vaccination may have protective effects

The researchers found that the risk of hospitalisation from infectious diseases did not differ among vaccinated versus unvaccinated girls and women.

In fact, the risk ratio was 0.92, indicating that more unvaccinated than vaccinated girls and women were hospitalised with an infectious disease.

However, the difference was small, and after 3 months, the unvaccinated and vaccinated groups did not differ.

“Fortunately, most vaccine safety studies are negative – meaning no association. These negative studies may still attract a lot of attention, simply because vaccination is so important for public health and people want to clarify these questions. In our study, we can conclude that HPV vaccination does not seem to alter the risk of being hospitalised with an infectious disease caused by another virus or bacterium in Denmark, which is reassuring. However, this does not mean that we can currently exclude any association for other non-live vaccines,” concludes Anders Hviid.

Quadrivalent human papillomavirus vaccination and non-targeted infectious disease hospitalisation: population-based self-controlled case series analysis” has been published in The Lancet Regional Health Europe. The Novo Nordisk Foundation awarded lead author Anders Hviid a Hallas-Møller Scholarship in 2014 and a Data Science Investigator grant in 2020.

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