U.N. agencies and the GAVI vaccine alliance said on Friday that 80 million children in at least 68 countries may be at risk of diphtheria, measles and polio because routine immunisation efforts have been thrown into disarray by travel restrictions, delivery delays, and parents’ fear of leaving home.

If these continue to disrupt programmes, GAVI chief executive Seth Berkley said, much of the world may also be unprepared to administer vaccines against COVID-19 being developed by more than 100 projects worldwide.

“If we neglect the supply chains and immunization infrastructure that keep these programmes running, we also risk harming our ability to roll out the COVID-19 vaccine that represents our best chance of defeating this pandemic,” Berkley told reporters via a World Health Organization conference call.

London is hosting a virtual Global Vaccines Summit on June 4 where GAVI is seeking $7.4 billion for 2021-2025 to immunise an additional 300 million children.

Fragile health care systems are coming under strain from COVID-19, with cases in parts of Africa escalating and Brazil’s count of people stricken now at over 300,000, with over 20,000 deaths.

“South America has become a new epicentre of the disease,” said Mike Ryan, the WHO’s top emergencies expert.

Ryan took issue with the Brazilian government’s approval of the malaria medicine hydroxychloroquine for broad use against COVID-19, which he said goes against WHO guidance to wait for trial results, since the drug has deadly heart risks and remains unproven.

WHO Director-General Tedros Adhanom Ghebreyesus, also on the call, did not address the latest U.S. demands that his organization immediately begin investigating the novel coronavirus’s source, as well as the WHO’s pandemic response.

President Donald Trump, a WHO critic, has threatened to permanently withdraw U.S. funding. (Reporting by Stephanie Nebehay and John Miller; Editing by Catherine Evans and Jan Harvey)