There is now an  of measles spreading in various regions globally, as the Covid pandemic has led to a steady decline in vaccination coverage and weakened surveillance of the disease, the World Health Organization and the Centers for Disease Control and Prevention said Wednesday.

Measles is one of the most contagious human viruses and is almost entirely preventable through vaccination. However, it requires 95% vaccine coverage to prevent outbreaks among populations.

A record high of nearly 40 million children missed a measles vaccine dose in 2021 due to hurdles created by the Covid pandemic, the WHO and the CDC said in a joint report.

While measles cases have not yet gone up dramatically compared to previous years, now is the time to act, the WHO’s measles lead, Dr. Patrick O’Connor, told Reuters.

“We are at a crossroads,” he said Tuesday. “It is going to be a very challenging 12-24 months trying to mitigate this.”