Every year, Stephen Lim and his colleagues at the University of Washington compile and analyze health data from every country on the planet to come up with a sort of global report card.

Year after year, one of the biggest success stories has been the vaccination of children.

"We've really seen this steady progress in increasing the fraction of children who are receiving ... in particular, the basic vaccines — diphtheria, tetanus and pertussis," Lim says.

The progress is especially notable in poor countries. Back in the 1970s, fewer than 5% of those children were getting basic vaccinations. Last year their coverage was above 80%.

Then the pandemic hit — grounding planes that transport vaccines, sidelining health workers who administer them, prompting parents to stop taking their children for checkups out of fear they'd get infected with the coronavirus at the doctor's office.

So Lim's team wanted to figure it out — just how big of an impact on vaccinations has all this been having?

Their findings were released in a joint report with the Gates Foundation this week. (The foundation is a sponsor of NPR and this blog).

The results are alarming: Compared to last year, the percentage of kids worldwide who got their basic vaccines has dropped from 84% to 70%.

"We haven't seen that level of coverage in 25 years," notes Lim.

One caveat: To come up with this estimate so quickly, Lim's team had to extrapolate from a less comprehensive set of data than they usually use. That's one reason they're not releasing the new vaccination rates country by country. But overall, Lim says, "This effect is not isolated to any one region of the world. It's something that's really affected all countries," rich and poor alike.

There is, however, reason to hope that vaccinations could return to prior levels as soon as the pandemic is over. For instance, Lim's team has found that in places where social distancing has eased and cellphone data indicates people are starting to move around again, there's been a corresponding rise in vaccine coverage. But he says it's possible that trend will not hold across all countries.

Seth Berkley, head of the Global Alliance for Vaccines and Immunization, or Gavi, is particularly worried about children in vulnerable situations. For instance, he says, "Those living in urban slums, which are growing rapidly around the world, or those living as displaced people in refugee camps."

It has taken years of effort by Gavi, other international partners and governments to extend vaccinations to these hard-to-reach children. "So the question is," says Berkley, "are some of those groups that we've been fighting to get into the system over the last decade or two going to again become difficult [to reach]? And therefore it's going to take us a long time to reach them."

Also, even if vaccination rates are quickly brought back up, what of those who missed their chance this year?

Damian Walker, a health economist with the think tank Center for Global Development, is not optimistic: "I think there's going to be a lost generation of kids who never get what they needed."

Walker notes that it may take a while for the impact of this gap to become clear. "When you vaccinate a kid, you're really saving them from a death that might occur in a year's time and for some diseases in 20 or 30 years' time," he says.

In fact, Walker is part of a team now working to estimate how many indirect deaths the pandemic will ultimately cause. One thing is already clear, he says: "The collateral damage from this virus has been extensive."

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