Child vaccination rates in the United States fell during the COVID-19 pandemic as many children skipped doctors appointments and states eased vaccine requirements during remote learning, according to a government study released on Thursday.

During the 2020–21 school year, vaccination coverage among kindergartners nationwide for three required vaccines was approximately 1% lower than the previous school year, according to the study conducted by researchers from the U.S. Centers for Disease Control and Prevention (CDC).

"As schools return to in-person learning, high vaccination coverage is necessary to continue protecting students from vaccine-preventable diseases," the study's authors said.

The researchers looked at coverage for three commonly required vaccines: the MMR vaccine to prevent measles, mumps, and rubella; DTaP, which prevents diphtheria, tetanus, and acellular pertussis; and the varicella shot for chickenpox.

Coverage for all three vaccines decreased in a majority of states to about 94%, just under the target of 95%, the CDC said.

“This might not sound like much," Georgina Peacock, acting director of CDC’s Immunization Services Division told reporters on a call. "But it amounts to at least 35,000 more children across the United States that entered kindergarten without documentation of complete vaccination against common diseases like measles, whooping cough, and chickenpox.”

The study included data collected for the 2020–21 school year by state and local immunization programs in 47 states and the District of Columbia.

The study authors noted some limitations to their data, including variations in states' vaccine requirements and documentation processes, non-inclusion of three states and barriers created by the pandemic, such as the shift to virtual learning.