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Routine childhood vaccinations among kindergartners declined in the 2021-2022 school year, contributing to a 2-percentage point decrease in vaccine coverage in this age group since the start of the COVID-19 pandemic, CDC researchers found.

Among all U.S. kindergartners last year, approximately 93% received their measles, mumps, and rubella (MMR) shot, the vaccine for diphtheria, tetanus, and acellular pertussis (DTaP), and the poliovirus and varicella vaccines, reported Ranee Seither, MPH, of the CDC's National Center for Immunization and Respiratory Diseases in Atlanta, and colleagues.

Overall coverage for these immunizations has dropped 1 percentage point per year since 2019, with vaccination against all four illnesses declining in most states, Seither and colleagues wrote in the .

"While this might not sound significant, it means nearly 250,000 kindergartners are potentially not protected against measles alone," Georgina Peacock, MD, MPH, acting director of the CDC's immunization services division, said at a press conference. "We know that measles, mumps, and rubella vaccination coverage is the lowest it has been in over a decade."

Just last year, communities in Minnesota and Ohio experienced measles outbreaks that resulted in child hospitalizations.

"These outbreaks were preventable," Peacock said. "The best way to prevent these diseases and their devastating impact on children is vaccination."

New York also discovered, for the first time in close to a decade, a case of paralytic polio in an individual who was not vaccinated.

The decline in vaccine coverage is not driven by an increase in exemptions, said Sean O'Leary, MD, chair of the American Academy of Pediatrics' committee on infectious diseases. Overall, 2.6% of kindergarten students had vaccine exemptions, with the majority of those exemptions being nonmedical. However, 4% of U.S. kids who were not exempt still had not received their MMR vaccine, the study found.

"I think it's complicated, why we've seen this drop," O'Leary said in the press conference. "Certainly misinformation is a problem, has always been a problem."

O'Leary added that researchers are still trying to understand the extent to which disinformation about the COVID-19 vaccines has led to misinformation about other childhood vaccinations, noting that misinformation about routine vaccinations has circulated for many years.

Peacock noted that pandemic disruptions to the healthcare system, as well as on schools' ability to collect vaccine documentation, could also be contributing to a decrease in reported childhood immunization rates in recent years.

Seither's group recognized a few limitations of their study, noting that state comparisons were limited because of differing vaccine requirements. Additionally, they noted that vaccination coverage and exemption rates could be over- or underestimated because of inaccurate or missing documentation from schools during this time.

Although vaccine coverage among kindergarten students has declined in recent years, routine immunizations among toddlers has remained stable, according to a separate study by Holly Hill, MD, PhD, also of the National Center for Immunization and Respiratory Diseases, and colleagues.

Overall, 70% of children born between 2016 and 2019 were up-to-date with their seven-vaccine series by the time they were 2 years old, Hill's group wrote in the .

Compared with babies born from 2016-2017, those born from 2018-2019 had higher rates of a majority of routine vaccinations. Rates were over 90% each for having at least three doses of the polio shot, one dose of MMR, three doses of hepatitis B, and one dose of varicella vaccine. Coverage was lower for having at least two doses of the influenza (63.9%) and hepatitis A (47.3%) vaccines among kids born in 2018-2019.

As far as the percentage of toddlers who have not received any vaccines, "that number is actually going down," O'Leary said. "So parents are still getting their children vaccinated, the vast majority are."

The percentage of children who were completely unvaccinated was just under 1%, down about 0.4 percentage points from 2016-2o17.

Hill and colleagues did not detect any decreases in routine vaccine coverage among toddlers related to the COVID-19 pandemic, during which the youngest children included in this analysis reached 2 years old. However, while vaccination rates have remained steady in recent years, there were still persistent -- and in some cases, widening -- disparities among children who resided in rural areas, came from lower-income families, did not have insurance, or who were in Black or Hispanic populations.

For example, vaccine coverage for the seven-vaccine series dropped 4 to 5 percentage points more among children who lived below the federal poverty level or in rural areas, with immunizations declining among kids in these two groups during the pandemic.

"A particular concern are these unfortunate disparities described," O'Leary stated, noting that barriers such as lack of access to transportation, healthcare services, or paid time off work create significant challenges for some families to get their children immunized.

Hill's group noted that their findings could be limited by selection bias, because of a low household interview response rate. Additionally, vaccine coverage estimates might be over- or underestimated if vaccination providers did not respond to questionnaires or if administered vaccines were not documented correctly.

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