Nearly 23 million children around the world missed out on routine childhood vaccinations last year due to service disruptions from the pandemic, the World Health Organization and UNICEF report.

In a new analysis released Thursday that highlights data from around the world, the two organizations said immunization rates among children fell in many Asian and Middle Eastern countries.

India represented the largest increase in children not receiving their first diphtheria, tetanus and pertussis (DTP) vaccine from 2019 to 2020. In 2020, India reported more than 3 million children didn't receive their first DTP vaccine, up from the 1.4 million children who didn't get the shot in 2019, according to the data.

And the trend remains a serious problem around the world. There was an increase in the number of children who missed important first vaccine doses in 2020 globally, the organizations said, with millions more children missing out on later vaccines, too.

Children usually receive their first dose of the DTP vaccine when they are under age 7. The first dose of the measles vaccine is usually received between 12 and 15 months of age.

The WHO says the numbers released this week show the impact of the COVID-19 pandemic on even routine health services such as vaccines and checkups, as well as immunization outreach, around the world.

The worst impact is on children who live in conflict-ridden areas, remote places or in slums. Those are areas where access to basic health and social services are extremely limited and where the WHO and UNICEF say up to 17 million children likely didn't receive a single vaccine during the year.

COVID-19 has made a "bad situation worse," Henrietta Fore, UNICEF's executive director, said.

She said, "This evidence should be a clear warning — the COVID-19 pandemic and related disruptions cost us valuable ground we cannot afford to lose — and the consequences will be paid in the lives and well-being of the most vulnerable."

Childhood vaccination rates have stalled for years

Global health officials have seen worrying signs that efforts to immunize children against preventable illnesses were failing even before the pandemic, according to this most recent report.

For example, before the onset of the coronavirus the number of children globally to get at least the first shot of the measles vaccine stalled for more than a decade at around 86%.

The WHO and UNICEF estimated that fewer than 70% of children received the recommended second dose of measles. The global health organization recommends immunization levels of 95% to protect against an outbreak of measles.

"Even as countries clamour to get their hands on COVID-19 vaccines, we have gone backwards on other vaccinations, leaving children at risk from devastating but preventable diseases like measles, polio or meningitis," said Dr. Tedros Adhanom Ghebreyesus, the WHO director-general.

In 2018, more than 140,000 people died from measles during a surge in cases around the world among young children who were not vaccinated against the illness. Almost half of all measles cases worldwide in 2018 came from the Democratic Republic of Congo (DRC), Liberia, Madagascar, Somalia and Ukraine.

In South and North America and the Caribbean, the WHO reports that vaccination levels continue to fall. Just 82% of children are fully vaccinated with DTP, down from 91% in 2016.

Health officials believe funding shortfalls, misinformation surrounding vaccine safety and regional instability are contributing to the decrease in childhood immunization rates.

Meanwhile, outbreaks of preventable illnesses among children in the U.S. have cropped up in recent years. In 2019, there was an outbreak of measles in 31 states. About 1,280 individual cases were confirmed, according to the Centers for Disease Control and Prevention. That was the greatest number of cases reported in the U.S. since 1992. Most cases were among people who weren't vaccinated against measles.

Ghebreyesus said, "Multiple disease outbreaks would be catastrophic for communities and health systems already battling COVID-19, making it more urgent than ever to invest in childhood vaccination and ensure every child is reached."

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