A record number of American kindergarten students started school last year with an exemption from one of the key vaccines health authorities require, according to new data from the Centers for Disease Control and Prevention.

In the report published Thursday, the CDC examined immunization program data to assess vaccination coverage and exemption status for four childhood vaccines:

• Measles, mumps, and rubella vaccine (MMR) 
• Diphtheria, tetanus, and acellular pertussis vaccine (DTaP) 
• Poliovirus (polio) vaccine 
• Varicella vaccine (protects against chickenpox)

Among children enrolled in public and private kindergarten during the 2022-23 school year, the report found vaccination coverage remains lower than the pre-pandemic levels, at 93%, down from 95%. 

Vaccination exemptions increased to 3% of kindergarten students — the highest exemption rate ever reported in the country — and a vast majority of those exemptions were not for medical reasons.

“Overall, 3.0% of kindergartners had an exemption (0.2% medical and 2.8% nonmedical) from one or more required vaccines,” the report noted. “Nonmedical exemptions account for (greater than) 90% of reported exemptions, and approximately 100% of the increase in the national exemption rate.”

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A medical exemption is allowed when a child has “a medical condition that prevents them from receiving a vaccine,” according to the CDC. Nonmedical exemptions, for religious or philosophical reasons, are allowed in all but three states, the agency says. In recent years, New York and California have passed laws clamping down on nonmedical exemptions after outbreaks of measles.

While the new report did not determine whether the uptick in nonmedical exemptions reflects an increase in opposition to vaccination or if parents are skipping the shots due to barriers or inconvenience, it does come at a time when vaccine hesitancy remains high, a sentiment amplified by anti-vaccine activists during the COVID-19 pandemic. 

The CDC stresses the importance of making sure children are fully vaccinated against common and sometimes serious infectious diseases before entering school, since clusters of undervaccinated kids can lead to outbreaks.