Vaccination delays among young children, combined with international travel, threaten to re-establish measles in the United States, where the virus was officially eliminated two decades ago.

More than 600 people in New York City contracted measles between October 2018 and July 2019, and 49 had to be hospitalized. The outbreak started after one unvaccinated child fell sick with the disease after returning home from Israel in September 2018. Although no deaths were reported, complications among those infected included diarrhoea, ear infections and pneumonia.

Jane Zucker at the New York City Department of Health and Mental Hygiene and her colleagues interviewed people who showed symptoms of measles and reviewed the immunization records of affected children.

The authors found that reduced vaccination rates in some neighbourhoods facilitated the spread of the disease. Among 37 children hospitalized with the virus, 35 had not received the measles, mumps and rubella vaccine. Most of those infected belonged to New York City’s orthodox Jewish community, which had been targeted by anti-vaccination groups — leading parents to shun immunization for their children, the researchers say. The outbreak cost New York City at least US$8.4 million.