Measles outbreaks are ongoing in the United States. As of 1 October 2026, 3,887 confirmed measles cases were reported in the United States in 2026. Among these, 3,869 measles cases were reported by 47 jurisdictions. There have been 42 new outbreaks reported in 2026, and 95% of confirmed cases are outbreak-associated. That is about 70% more cases than were recorded during the whole of 2025. New York has just declared a state of emergency as measles cases continue to rise.

Measles is caused by the measles virus. It can be transmitted by airborne droplet spread or by direct contact with the nasal or throat secretions of infected persons, and less commonly, by articles soiled with such secretions. Measles is a highly communicable infectious disease. A patient can transmit the disease to others from four days before to four days after the onset of the rash. The incubation period usually ranges from 7 to 18 days, but can be up to 21 days.

Vaccination against measles is the most effective preventive measure. Under the Hong Kong Childhood Immunisation Programme, children receive a two-dose course of measles vaccination. In general, people can be considered as non-immune to measles if (i) they did not have measles infection confirmed by laboratory test before, and (ii) they had not been fully vaccinated against measles or have unknown vaccination status.

Please visit the Centre for Health Protection’s Measles Webpage for more details.