Covid-19 vaccines may be less effective in people who have intestinal parasite infections, or roughly a of the world鈥檚 population. This is suggested by experiments in mice infected with parasitic worms, who developed significantly weaker immunity after covid-19 vaccines than mice without parasitic infections.

Previous research has shown that people with intestinal parasites have impaired immune responses to some vaccines, such as those for tuberculosis or measles. This is because the parasites suppress processes that vaccines trigger to confer immunity, such as the activation of pathogen-killing cells. Intestinal parasite infections are most prevalent in tropical and subtropical regions and often occur due to limited access to clean water and sanitation.

Scientists haven鈥檛 tested whether these pathogens reduce covid-19 vaccine effectiveness. at Washington University in St. Louis, Missouri, and his colleagues inoculated 16 mice with a covid-19 mRNA vaccine, half of which had been infected 12 days before with an intestinal parasite that only occurs in rodents. They gave each mouse a booster shot three weeks after the first shot.

About two weeks after the booster dose, the researchers analysed the animals鈥� spleens to measure the concentrations of CD8+ T cells 鈥� a special type of white blood cell important for clearing other cells infected by the SARS-CoV-2 virus. On average, the spleens of mice with intestinal parasites had roughly half the number of these cells as those without parasites, suggesting an impaired immune response to the vaccine.

The researchers repeated this vaccine process in a separate group of 20 mice 鈥� half of which had been infected with intestinal parasites 鈥� and exposed them to a highly infectious omicron subvariant of the SARS-CoV-2 virus. Five days later, vaccinated rodents with intestinal parasites had about 20 per cent more of the virus in their lungs, on average, than those without them.

Together, these findings indicate that intestinal parasites may reduce the efficacy of covid-19 vaccines in people. However, different types of intestinal parasites are known to affect immunity in different ways, says at the University of Utah. So, it is unclear if those that infect people would have a similar effect on covid-19 vaccination as those in mice. Plus, people tend to have multiple types of intestinal parasites at once, further complicating the picture, she says.

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Still, it is important to understand how parasitic infections alter immune responses to vaccination given their prevalence, and these findings suggest researchers may want to further evaluate vaccine efficacy in areas of the world where a high proportion of the population has intestinal parasites, says Fairfax.

AI training focused on identifying eggs from three types of parasitic worms: the roundworm Ascaris lumbricoides, the human whipworm Trichuris trichiura and hookworms such as Ancylostoma duodenale or Necator americanus.

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翱耻谤听New Scientist Book Club has been reading Lauren Beukes’s 叠谤颈诲驳别,听a thrilling sci-fi novel exploring neuroparasitology and the multiverse. This week our culture editor Alison Flood got to catch up with the Arthur C Clarke award-winning novelist to find out what inspired the creation of the ‘dreamworm’, how music theory influenced her novel and why she has a slice of a rat’s brain in her cupboard.

Bridge is the latest pick for New Scientist鈥檚 new book club, for which you can sign up here

Fossilised faeces of a crocodile-like predator living 200 million years ago reveal the animal was infected with multiple parasite species. Evidence of ancient parasites is notoriously hard to find in the fossil record, so this discovery can help give us a picture of how they spread from species to species.

Parasites infect animals鈥� soft tissues, which rarely preserve well over time. So at Mahasarakham University in Thailand and his colleagues analysed a sample of fossilised dung, also called a coprolite, that was first unearthed in 2010 from the Huai Hin Lat Formation in north-eastern Thailand.

鈥淚 wanted to know what鈥檚 inside the coprolite, so I decided to cut it open and examine its internal structure,鈥� says Nonsrirach.

The shape and contents of the faeces helped the researchers narrow down which creature it came from. They first photographed and measured the coprolite before hardening it with an epoxy resin. They then cut the log 鈥� 7 centimetres long and 2 centimetres thick 鈥� into thin, salami-like slices.

When the team examined the slides under the microscope, they found parasite eggs in a range of sizes and shapes trapped in the droppings. The eggs were mostly round and oval, and around the thickness of a human hair. The team suspects as many as six parasite species 鈥� including intestinal worms called nematodes from the order Ascaridida 鈥� are represented in the ancient faeces.

The researchers concluded that the excrement was probably left by an armoured, semi-aquatic reptile that looked like and lived similarly to a modern crocodile. 鈥淐onsidering that crocodiles appeared around 100 million years ago during the Late Cretaceous, it is likely that the coprolite came from a crocodile-like animal or one that co-evolved with crocodiles, such as phytosaurs,鈥� says Nonsrirach.

Based on the remains of ancient plants and animals also found in the area, the researchers estimate the specimen is from the early Late Triassic Epoch, around 237 million to 208 million years ago. 鈥淭his discovery is crucial for understanding the variety of parasites and how they interacted in ancient ecosystems,鈥� says Nonsrirach. He suspects the animal ingested the parasites by feeding on infected fishes, amphibians or other reptiles.