The widespread interruption of routine immunization programs around the world during the coronavirus pandemic is putting 80 million children under 1 year old at risk of contracting deadly, vaccine-preventable diseases, according to a report Friday by the World Health Organization, UNICEF and Gavi, the Vaccine Alliance.

The groups surveyed 129 poor and middle-income countries and found that 68 had some degree of disruption of vaccine services through clinics and through large inoculation campaigns.

Measles initiatives, for example, have been suspended in 27 countries, including Chad and Ethiopia, and polio programs are on hold in 38, including Pakistan and the Democratic Republic of Congo.

Many public health experts say they are worried that deaths from diseases including cholera, rotavirus and diphtheria could far outstrip those from Covid-19 itself.

The report highlighted warnings about polio, which had recently been all but eradicated, a hard-won victory that resulted from mass immunization programs that reached millions of children.

Dr. Seth Berkley, chief executive of Gavi, said that developing countries had made big gains in immunizations against numerous diseases in recent years. Before the pandemic hit, he said, more children in more countries had been protected against more vaccine-preventable diseases than ever before.

“Due to Covid-19, this immense progress is now under threat, risking the resurgence of diseases like measles and polio,” he said.

Restarting immunization programs is crucial not just for preventing more outbreaks of life-threatening diseases, he said: “It will also ensure we have the infrastructure we need to roll out an eventual Covid-19 vaccine on a global scale.”