As states across the country relax stay-at-home orders and people return to more normal routines, some researchers worry about a spike in vaccine-preventable diseases in addition to the coronavirus’s spread.

During the pandemic, the rates of childhood vaccinations have dropped significantly as many parents have been reluctant to schedule well-child visits at their doctors’ offices, for fear of contracting the coronavirus. As a result, children have fallen behind on vaccinations for diseases like measles and pertussis, better known as whooping cough.

According to a new study released by the Centers for Disease Control and Prevention, the vaccination rates in May for children under 2 years old in Michigan fell to alarming rates, including fewer than half of infants 5 months or younger.

Angela Shen, a research scientist at Children’s Hospital of Philadelphia and the co-author of the study, said the falling rates in Michigan were concerning and quite likely representative of trends throughout the country.

“Now, you’re not just dealing with COVID,” she said, referring to COVID-19, the disease caused by the coronavirus. “Now you’re contending with common vaccine-preventable diseases.”

Over the past two months, the risk of infection for diseases like measles might have been mitigated because most people, following stay-at-home orders, were not in proximity to one another. Now that some states are easing restrictions and allowing people to move about in their communities, there is a fear of outbreaks for diseases like influenza and especially measles.

“You are prone to potentially seeing measles outbreaks as communities and jurisdictions in Michigan — and arguably in other parts of the country — open up,” said Shen, a retired captain in the U.S. Public Health Service. “This is a big week for opening up, and public health wants you to come in and get your shots.”

The study used data from the Michigan Care Improvement Registry, which tracks immunizations within the state. It compared vaccination rates for children 5 months or younger on a typical day in May from 2016 to 2019, with the same day this year. It showed that before the pandemic, roughly two-thirds of children in that age group were up to date with their vaccinations; this year, the rate fell to 49.7%.

The study also showed that Michigan children on Medicaid were even less likely to be current on their immunizations. The largest disparity was seen among those 7 months or younger. The researchers found that only 34.6% children on Medicaid were up to date, compared with 55% of children in Michigan who were not on Medicaid.

Shen said the falling rates could jeopardize the herd immunity that communities have built up against a disease like measles. Public health officials estimate that a community vaccination rate from 93% to 95% is necessary to prevent a widespread outbreak of measles.

Recent measles outbreaks in the United States have raised fears that the disease could become endemic here again. It was declared eliminated in the United States in 2000.

Dr. Matthew L. Boulton, a professor of epidemiology and preventive medicine at the University of Michigan, who did not take part in the Michigan study, said the results were not surprising considering the suspension in preventive care in recent weeks. People were not able, or did not want, to visit doctors for routine checkups.

It is vital, though, that parents and guardians catch up on their children’s vaccinations as soon as possible, he said, because these lapses can become magnified over time; with so many more children unprotected, outbreaks may occur.

“I think the implications for childhood immunization are long term,” he said, “because it will take a substantial amount of time to make up for this.”

Boulton said the problem was global, too. He said that he does immunization work and research in China, India and some African countries, and that his partners there had said they were seeing the same phenomenon.

“It’s a really scary thought,” he said. “We’ve made tremendous progress around the world, especially in many low-income countries. This literally could set us back years in our control of vaccine-preventable diseases, in both high- and low-income countries.”

In the United States, state health departments and pediatricians use immunization registries to monitor vaccinations. The information can be used to contact the families that have fallen behind on vaccinations and urge them to follow up as soon as possible.

The Michigan study also noted that doctors could employ strategies to reduce the potential for coronavirus infection by creating separate rooms for healthy children and even by administering vaccinations to children in cars in parking lots. Those efforts could alleviate the fears among parents and improve the likelihood they catch up on their children’s vaccinations.

“We already had challenges keeping kids up to date,” Boulton said. “This two- or three-month gap will definitely exacerbate that.”

© 2020 The New York Times Company