Background 

• Pathogen : Measles (link information only in Swedish) is caused by the measles virus (MeV), a member of the genus Morbillivirus in the family Paramyxoviridae. It is one of the most contagious human viral pathogens. Infection typically presents with high fever, cough, coryza (runny nose), and conjunctivitis, followed by a characteristic maculopapular rash. Serious complications, including pneumonia and encephalitis, can occur, particularly in infants and immunocompromised individuals.

• Transmission: Measles spreads through airborne respiratory droplets and aerosols released when an infected person breathes, coughs, or sneezes. The virus enters through the mucous membranes of the respiratory tract or eyes. For more information, please see the dedicated page on the outbreak from the Swedish Health Agency (Folhälsomyndigheten, available only in Swedish).

• Sources and risk factors: Major risk factors include a lack of vaccination or incomplete vaccination, close contact with an infected individual, attendance at crowded events where exposure can occur, and international travel to areas where measles remains endemic. In this outbreak, the primary exposure event was attendance at the Urkult festival in Västernorrland. Most confirmed cases occurred among unvaccinated school-aged children and young adults.

• Seasonality: There is no seasonality to infections. Transmission depends primarily on population immunity and exposure to infected individuals, rather than season. In Sweden, outbreaks are uncommon due to high vaccination coverage (around 95%) and are typically associated with imported infections or exposure in groups with insufficient immunity.

Brief Summary of the Outbreak

The outbreak was first identified in August 2026, when five measles cases were reported in Sweden. Epidemiological investigations linked three of these cases to the Urkult festival held in Västernorrland from 30th July to 2nd August 2026. As surveillance and contact tracing continued, additional linked cases were identified across multiple Swedish regions. By 17th August, the number of confirmed cases had increased to 10, and by 25th August, 31 laboratory-confirmed cases had been reported from nine regions. Most infections occurred among unvaccinated individuals, highlighting the importance of maintaining high vaccination coverage.

Regional public health authorities continue contact tracing and monitoring to limit further transmission. Folkhälsomyndigheten has created a page on the outbreak (available only in Swedish).

Outbreak Timeline