A woman in South Korea gets tested for COVID-19 on Monday. As the pandemic continues to spread and the number of cases continues to break the record, the government has decided to implement the most stringent (fourth-level) prevention and control measures in Seoul, Gyeonggi, Incheon and other capital regions. Photo: VCG

The UN warned Thursday that a "perfect storm" was brewing, with a raging pandemic disrupting access to routine vaccinations, leaving millions of children at risk from measles and other deadly diseases.

A full 23 million children missed out on basic childhood vaccines in 2020, as routine health services were hit worldwide by restrictions aimed at controlling COVID-19 and many parents shunned the clinics that were open for fear of exposure to the virus.

It marks the highest number in over a decade and 3.7 million more than in 2019, according to data published Thursday by the World Health Organization and the UN's children's agency UNICEF. And the sharp decline in routine vaccinations comes as many countries have begun loosening restrictions even as the pandemic is far from over.

This has the potential of not only driving up COVID-19 transmission, but also of allowing otherwise vaccine-preventable diseases to begin spreading. That is because the restrictions in many countries have until now also provided a buffer protecting unvaccinated children against exposure to childhood diseases.

"In 2021, we have potentially a perfect storm about to happen," Kate O'Brien, head of the WHO's vaccines and immunization department, told reporters. She warned there was now "an accumulation of children who are not immune because they haven't received vaccines, and more and more transmission because of too early release of public health and social measures.

"This is the sort of perfect storm we're ringing the alarm bell about right now," O'Brien said, stressing WHO's "high concern about these very outbreak prone diseases."

"We need to act now in order to protect these children."

The data published Thursday revealed that rising numbers of children across all regions missed first vital vaccine doses in 2020 while millions more missed later vaccines.

Compared with 2019, 3.5 million more children missed their first doses of the three-dose diphtheria, tetanus and pertussis vaccine (DTP) while 3 million more children missed their first measles dose, the data showed.

Even more concerning perhaps, as many as 17 million children, mainly living in conflict-affected communities or in under-serviced remote areas or in informal slum settings, likely did not receive a single vaccine in 2020.

"The COVID-19 pandemic and related disruptions cost us valuable ground we cannot afford to lose," UNICEF chief Henrietta Fore said in the statement, cautioning that "the consequences will be paid in the lives and wellbeing of the most vulnerable."

She said even before COVID-19, "there were worrying signs that we were beginning to lose ground in the fight to immunise children against preventable child illness."