Pandemic Lockdowns Resulted in Stronger Immune Responses to Viruses

Research from Radboudumc shows that the lockdowns during the COVID-19 pandemic had an impact on people's immune response to microorganisms. During the lockdown, inflammation levels in the body were low, but afterwards the immune system responded more strongly to viruses and bacteria. The results have now been published in Frontiers in Immunology.

In this study, the researchers looked at the effects of various health measures that were introduced during the pandemic, such as lockdowns and vaccinations. The study was conducted among people with HIV and a control group consisting of people without HIV or other conditions. The researchers found that the inflammation values ​​in the blood of people from both groups were low during the lockdown. But when they brought the immune cells from the blood into contact with microorganisms such as viruses and bacteria in the laboratory, the immune system responded more strongly.

Hygiene hypothesis

As a possible explanation for this immune response, Radboudumc professor Mihai Netea mentions the hygiene hypothesis. This hypothesis investigates whether the lack of exposure to environmental factors contributes to the increase in the number of people with autoimmune diseases and allergies, among other things. Netea: 'In our daily lives, we continuously come into contact with all kinds of micro-organisms. As a result, we train our immune system, which recognizes which micro-organisms are dangerous and which are harmless. During the lockdown, we missed that interaction, people were indoors a lot and there was less contact between each other. After the lockdown, when people sought each other out again and came into contact with each other, the immune system reacted more strongly to micro-organisms.'

About the design of the study

This study was initiated by the Radboudumc and three other Dutch HIV treatment centers, which started a large study of people with HIV. The recruitment of participants for that study was between October 2019, just before the COVID-19 pandemic broke out, and October 2021. 1895 people with HIV are participating in this so-called 2000HIV study. This study is part of a large research project into the functioning of the immune system and the variety of immune responses.

The study participants were divided into four groups:

• 368 individuals were included for the pandemic
• 851 individuals were included after the lockdown, and before any vaccination or COVID-19 infection
• 175 people who had had a COVID-19 infection
• 404 vaccinated people

The participants donated blood, among other things, which was examined for the degree of inflammation. The researchers also looked at the interaction between isolated blood cells and viruses and bacteria in the laboratory. Professor Andre van der Ven: 'The results of this study say something about people living with HIV, but we also looked at a healthy control group. We saw comparable results there, which means that the effects may apply to society as a whole. However, more research is needed on this group.'

Being aware of impact

The study also found that the vaccines and COVID-19 infection affected the immune system’s response. However, these effects were small and short-lived, Netea explains, and were much smaller than the impact of the lockdowns on the immune system’s effects. Netea: ‘We need more knowledge about social conditions that may affect our defenses. During the pandemic, the lockdowns were necessary, especially in the beginning. In addition, we need to investigate whether a lockdown can have adverse effects, and how we can possibly reduce or prevent these effects. This way, we can optimally use drastic social measures in a possible future pandemic.’

Reference: Otten T, Jiang X, Gupta MK, et al. Impact of COVID-19, lockdowns and vaccination on immune responses in a HIV cohort in the Netherlands. Front Immunol. 2024;15. doi: 10.3389/fimmu.2024.1459593

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