Measles deaths globally spiked by more than 40% last year and cases rose after vaccination levels dramatically dropped during the pandemic, leading health agencies said. The highly infectious disease triggered epidemics in 37 countries last year, versus 22 countries in 2021. It sickened 9 million children and killed 136,00, mostly in poorer countries, the World Health Organization and the U.S. Centers for Disease Control and Prevention said in a new report.

The number of measles cases also rose by nearly 20% after immunization levels dropped to their lowest in 15 years during the pandemic, the agencies said.

“The increase in measles outbreaks and deaths is staggering, but unfortunately, not unexpected given the declining vaccination rates we’ve seen in the past few years,” said CDC’s John Vertefeuille, said in a statement.

Two doses of the measles vaccine are highly protective against the disease. Children in developing countries in Africa, Southeast Asia, Latin America and India are at highest risk. WHO and CDC said that immunization rates in poorer countries are about 66%, “a rate that shows no recovery at all from the backsliding during the pandemic.”

Measles is among the most infectious diseases known and spreads in the air when an infected person coughs or sneezes. It is most common in children under 5. Symptoms include fever, cough, runny nose and a distinctive rash.

Most deaths are due to complications like encephalitis, severe dehydration, serious breathing problems and pneumonia. Complications are most likely in young children and adults over 30.

The disease has also surged in some rich countries in recent years. British health authorities warned in July that there was an extremely high risk of outbreaks in London, with some areas of the capital reporting that only 40% of children were vaccinated.

Immunization rates against measles in the U.K. have never fully recovered since spurious claims that linked the vaccine to autism were made by discredited British doctor Andrew Wakefield more than two decades ago. No scientific studies have ever confirmed the link, but Wakefield’s research led to millions of parents worldwide abandoning the shot.