“During 2023 and 2024 multiple European countries, including the UK, have reported an increase in the number of measles infections,” the agency wrote in a statement.

“Measles is extremely contagious, and even though there are few cases in Sweden, sometimes unvaccinated people are infected on trips abroad, spreading it once they return home.”

There is an effective vaccine against measles, the MMR vaccine (MPR in Swedish), which also provides cover against mumps and rubella, one dose of which is offered to children at 18 months of age, and another once they start school in year one or two.

Although the agency mentions that cases are rising in other European countries, the UK is the only country it specifically names.

Anti-vaccine conspiracy theories are spreading in the UK, according to The Guardian, with the percentage of children under 5 in London who have received both doses of the MMR vaccine 9.1 points lower than ten years ago.

This has led to an increase in cases in the country, which the UK Health Security Agency (UKHSA) recently predicted could lead to between 40,000 and 160,000 cases in London alone.

In Sweden, the situation is different.

“So many people are vaccinated here that the risk of larger outbreaks is low,” state epidemiologist Magnus Gisslén wrote in a statement.

“However, unvaccinated people do run a risk of becoming infected during trips to countries with lower vaccination rates and an ongoing spread of infection. With an increased spread of infection in multiple European countries, it’s important to check your vaccinations before travelling abroad.”

Children who have not yet received an MMR vaccine can do so from 9 months of age if they are due to travel abroad to an area with an increased risk of infection, with the vaccine offered to children as young as 6 months if there is an exceptionally high risk, the agency writes.

Adults who have not had measles or have only had one dose of the vaccine are also advised to get vaccinated, especially if they are planning a trip abroad. There’s no need to get a booster after the second dose, even if it was given a long time ago.

“Measles is one of the most contagious illnesses in existence, and it can be dangerous for the unvaccinated, especially for small children and people with a weakened immune system,” Gisslén added.

“The vaccine on offer provides very good protection, and we have a well-functioning childhood vaccination programme. That’s why, thankfully, we see so few cases of the illness in Sweden today.”

“One in ten children who get measles will get complications, and sometimes it can be fatal,” UKHSA measles lead Vanessa Saliba told The Guardian. “And sometimes it can be fatal. But it’s completely preventable with a vaccine. Every case is a real shame.”