The threat of dangerous measles outbreaks is high and progress toward eliminating the disease has declined as more than 22 million infants globally failed to get their first measles vaccine dose last year, according to a joint statement from the World Health Organization and the Centers for Disease Control and Prevention.

Last year's figure is three million more than in 2019, representing the largest increase in two decades and creating dangerous conditions for outbreaks to occur, the statement added.

Moreover, measles surveillance also declined with the lowest number of specimens sent for laboratory testing in more than a decade.

Two-thirds of children who missed out on the vaccine live in just 10 countries: Afghanistan, Angola, Brazil, the Democratic Republic of Congo, Ethiopia, India, Indonesia, Nigeria, Pakistan and the Philippines.

The COVID-19 pandemic was cited as a major factor in the disruption of general immunization campaigns with both institutions calling for a return to pre-pandemic levels of immunization.

"The COVID-19 pandemic caused significant disruptions to immunization services and changes in health-seeking behaviors in many parts of the world. While the measures used to mitigate COVID-19 – masking, handwashing, distancing - also reduce the spread of the measles virus, countries and global health partners must prioritize finding and vaccinating children against measles to reduce the risk of explosive outbreaks and preventable deaths from this disease," the statement said.

Measles is one of the world's most contagious human viruses but is almost entirely preventable through vaccination.

It is estimated that more than 30 million deaths globally have been averted in the last two decades because of the vaccine.

CDC Global Immunization Director Kevin Cain said the likelihood of measles-related deaths and serious complications in children were increased by large numbers of unvaccinated children, outbreaks of measles, and disease detection and diagnostics diverted to support the response to the COVID-19 pandemic.

"We must act now to strengthen disease surveillance systems and close immunity gaps, before travel and trade return to pre-pandemic levels, to prevent­­ deadly measles outbreaks and mitigate the risk of other vaccine-preventable diseases."

Though the number of measles cases dropped in 2020 to 7.5 million, Dr. Kate O'Brien, the director of WHO's department of immunization, vaccines and biologicals, warned "evidence suggests we are likely seeing the calm before the storm as the risk of outbreaks continues to grow around the world."

"It's critical that countries vaccinate as quickly as possible against COVID-19, but this requires new resources so that it does not come at the cost of essential immunization programs," O'Brien said.

"Routine immunization must be protected and strengthened; otherwise, we risk trading one deadly disease for another."

(With input from agencies)