Measles cases in Pennsylvania have risen to 1,004, with the outbreak spreading and a fifth death reported. Here is what you need to know about one of the worst US measles outbreaks in decades.

The state has recorded 198 hospitalisations, and 106 new cases were added in just the last seven days. Lancaster County is the hardest hit with 391 cases. Five people have died — all were unvaccinated. More than 99 per cent of cases are in unvaccinated people.

Nationally, the CDC has counted 3,887 measles cases in the US in 2026 — the most since the 1989-91 epidemic. Health officials blame falling vaccination rates and misinformation.

The good news: the MMR vaccine is 97 per cent effective at preventing measles. Doctors urge anyone unsure of their vaccination status to check with their provider, especially before travel. Measles spreads through the air and is one of the most contagious diseases known — but it is also one of the most preventable.

Sources: reuters.com; sourcefirstnews.com; usatoday.com.