U.S. kindergarten vaccination rates dipped last year and the proportion of children with exemptions rose to an all-time high, according to federal data posted Wednesday.

The share of kids exempted from vaccine requirements rose to 3.3%, up from 3% the year before. Meanwhile, 92.7% of kindergartners got their required shots, which is a little lower than the previous two years. Before the COVID-19 pandemic the vaccination rate was 95%, the coverage level that makes it unlikely that a single infection will spark a disease cluster or outbreak.

The changes may seem slight but are significant, translating to about 80,000 kids not getting vaccinated, health officials say.

The rates help explain a worrisome creep in cases of whooping cough, measles and other vaccine-preventable diseases, said Dr. Raynard Washington, chair of the Big Cities Health Coalition, which represents 35 large metropolitan public health departments.