Recent studies indicate that Covid-19 vaccines may be less effective for individuals suffering from intestinal parasite infections, affecting around a quarter of the global population. Experiments conducted on mice infected with parasitic worms revealed a marked decrease in immunity following vaccination compared to their uninfected counterparts.
Previous research has established that intestinal parasites can impair immune responses to various vaccines, including those for tuberculosis and measles. This suppression occurs because parasites hinder the immune processes that vaccines aim to activate, specifically the mobilization of pathogen-fighting cells. Intestinal parasite infections are notably prevalent in tropical and subtropical regions, often linked to inadequate access to clean water and sanitation.
In a recent experiment, researchers at Washington University in St. Louis inoculated 16 mice with a Covid-19 mRNA vaccine, half of which had been infected with an intestinal parasite 12 days prior. Following a booster dose three weeks later, analysis of the mice’s spleens showed that those infected with parasites had about half the concentration of CD8+ T cells—crucial for combating SARS-CoV-2—compared to healthy mice, suggesting a weaker immune response.
A second group of 20 mice underwent a similar vaccination process, where half also had intestinal parasites. When exposed to an infectious omicron subvariant of the SARS-CoV-2 virus, vaccinated mice with parasites showed approximately 20% more virus present in their lungs five days post-exposure than those without parasitic infections.
These findings raise concerns about the potential impact of intestinal parasites on the efficacy of Covid-19 vaccines in humans. However, the exact effects may vary, as different types of intestinal parasites influence immune response in unique ways. Moreover, individuals often harbor multiple types of parasites simultaneously, complicating the understanding of this issue. It remains vital to explore how parasitic infections affect vaccine responses, particularly in regions with high rates of intestinal parasites, to ensure effective public health strategies moving forward.
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