More than 22 million infants across the globe didn’t get their first measles vaccine dose last year, according to a joint statement Wednesday from the World Health Organization and the Centers for Disease Control and Prevention.

Two-thirds of those children live in just 10 countries: Nigeria, India, the Democratic Republic of the Congo, Ethiopia, Indonesia, Pakistan, Angola, the Philippines, Brazil and Afghanistan.

Even in countries with high vaccination rates, anti-vaccine sentiment has led to outbreaks in some communities. In 2019, for example, the United States saw the highest number of preventable measles cases since 1992, according to the CDC.

Measles, one of the most contagious viruses in the world, is “almost entirely preventable” through the two vaccine doses, the WHO and CDC said.

Globally in 2019, 19 million infants missed their first dose; this increase to 22 million marks the biggest jump in two decades, which creates “dangerous conditions for outbreaks,” the organizations warned.

Only 70% of kids received their second dose last year, which is well below the 95% threshold needed to protect communities, the organizations said.

The number of measles cases actually dropped in 2020 to 7.5 million, but Dr. Kate O’Brien, the director of WHO’s department of immunization, vaccines and biologicals, warned in a statement, “evidence suggests we are likely seeing the calm before the storm as the risk of outbreaks continues to grow around the world.”

“It’s critical that countries vaccinate as quickly as possible against COVID-19, but this requires new resources so that it does not come at the cost of essential immunization programs,” O’Brien said. “Routine immunization must be protected and strengthened; otherwise, we risk trading one deadly disease for another.”