The World Health Organization warned Monday, April 27 that children across the world will die as the coronavirus pandemic forces some countries to temporarily halt vaccinations for other deadly diseases such as polio, CNBC reports.

At least 21 countries are reporting vaccine shortages as a result of travel restrictions meant to curb the spread of the Covid-19 pandemic, WHO Director-General Tedros Adhanom Ghebreyesus said during a press conference at the agency’s Geneva headquarters. “The tragic reality is children will die as a result.”

Just as immunization has been postponed in some countries, heath-care services for other diseases, such as malaria, have been disrupted, Tedros said, noting that the number of malaria cases in sub-Saharan Africa could double.

Tedros urged member countries to help ensure vaccination programs are fully funded, saying the Global Alliance for Vaccines and Immunization will need $7.4 billion to immunize 300 million children with 18 vaccines by 2025.

“When vaccination coverage goes down, more outbreaks will occur,” Tedros said.