Measles, which once killed an estimated 2.6 million people a year, is still killing almost 90,000 people a year according to the World Health Organization (WHO), and may be endemic again in the Americas, according to the latest data from the Pan American Health Organization.

Measles is a virus that people transmit through air droplets when they breathe. It affects mostly children, and mostly in populations with low vaccination rates.

Venezuela’s measles outbreak, now numbering around 1842 people, is just over one year old, meaning that by the standards of global health authorities, it’s no longer just an outbreak. A years’ local transmission makes a disease endemic, as opposed to cases brought by travelers. Whenever health organizations formally re-designate Venezuela’s measles status, it will take the region of the Americas off the list of ‘measles-free’ regions.

The World Health Organization declared the Americas endemic measles-free in late 2016. That followed a 16-year global mass vaccination campaign.

Venezuela’s government is expanding measles vaccinations, it announced late last month. When a high enough fraction of the population is vaccinated, it makes it almost impossible for the disease to spread, even if it is brought in from time to time by travelers.

The United States, for example, reports some 107 confirmed cases of the measles, but they are likely to have foreign origins within the last 12 months. If populations in the U.S. lower their vaccination rates, however, it will be easier for measles to thrive without foreign transmission.