Almost 23 million children missed out on routine vaccines last year due to the COVID-19 pandemic.
That's the highest number in over a decade, U.N. agencies said on Thursday (July 15).
It's fueling outbreaks of preventable diseases like measles, polio and many more.
Here's UNICEF's immunization chief, Ephrem Lemango:
"These latest data show an alarming increase in the number of children who did not receive any vaccine at all, which we call them zero-dose children, putting faith of million of young lives in the balance. Most of these children that missed their first dose of vaccine live in communities affected by conflict and crisis, live in communities that are underserved, remote…cases and they live in informal slum settings, particularly in urban poor areas."
Measles is one of the world's most contagious diseases - it can be fatal in children under five.
The World Health Organization say it's especially risky in African and Asian countries with weak health systems.
Polio can cripple a child for life.
The WHO and the U.N. said in an annual report that the gap in global vaccination coverage has set up a "perfect storm".
Meaning children are left more vulnerable to infection, just as countries begin to ease their COVID restrictions.
10 countries account for the majority of the 22.7 million children left unvaccinated or under-vaccinated against diphtheria, tetanus, and pertussis in 2020.
That's 3.7 million more than in 2019 and the most since 2009.
The report added that 66 countries postponed at least one vaccine campaign against preventable diseases.
Some are now running catch-up programs.
India, Nigeria, Afghanistan, Mali, Somalia and Yemen, are among the countries most affected by the vaccine backslide.
The WHO has urged countries not to lift public health and social distancing measures prematurely as they begin to emerge from the health crisis.