The number of children getting routine vaccinations has plummeted, setting the stage for what doctors fear could be a resurgence of preventable diseases.

In Minnesota, there's been a 70% drop in measles vaccine doses given compared with a year ago, according to state health officials.

Nationwide, the number of measles shots given by eight large health care systems dropped significantly one week after President Donald Trump declared a pandemic emergency on March 13, according to two researchers at the Bloomington-based HealthPartners Institute.

A federal program that supplies vaccines to about half the nation's children has seen orders for routine non-influenza vaccines drop by 2.5 million this year, according to the study released Friday by the Centers for Disease Control and Prevention.

"These data definitely show troubling decreases," said Dr. Malini DeSilva, one of the study's authors. "This indicates that many children may become vulnerable to these vaccine-preventable diseases."

The decrease in immunizations comes at a time when visits to primary care clinics are down substantially, partly out of fear about being exposed to COVID-19 but also because some might think it violates the spirit of stay-home orders.

"There certainly is concern and worry. At the same time we've also heard from families that really do want to make sure that their children are up to date on essential vaccines," said Dr. Dawn Martin, a pediatrician with Hennepin Healthcare.

Some clinics reserve morning appointments for well-child visits that include vaccinations, while the afternoon slots go to children who are ill. Vaccines are also being given in tents or in drive-through arrangements that keep children out of the clinics.

"I think that most clinics and most health systems have really gone to great lengths to try to make the clinic environment as safe as possible," Martin said.

Federal health officials recommend that clinics with limited capabilities, such as a shortage of personal protective equipment like masks, should prioritize care for newborns and vaccination of infants and young children through the age of 2.

"Many of these diseases affect infants and younger children more seriously than older children," Martin said.

It appears that efforts to vaccinate the youngest children are having some effect.

After falling initially in mid-March, the number of measles doses has steadily risen for those 24 months and younger, although it is still below levels seen in January.

"It does seem like some of the strategies pediatric practices have put in place to prioritize well-child visits do seem to be working," DeSilva said.

Depending on the type of shot, the measles vaccine also protects against mumps, rubella or varicella, also known as chickenpox.

By the last week of March, just 865 doses of the measles vaccine were given in Minnesota, according to the Minnesota Department of Health. That's a 71% decline from the previous year.

Measles, along with pertussis, or whooping cough, are particularly contagious.

"If the level of immunization coverage drops in the population then those are the circumstances under which we see outbreaks occur," said Martin, who sits on the board of the Minnesota chapter of the American Academy of Pediatrics.

"We certainly have a challenge with COVID and coping with the pandemic, but on top of that we don't really need a measles outbreak or more pertussis," she said.

Pertussis is circulating within the state, with 129 cases so far this year and 555 infections in 2019.

But measles would need to be imported from elsewhere, usually by an infected traveler. The decrease in travel worldwide could lessen the likelihood of measles taking hold here, but outbreaks often start with one infected person crossing paths with someone who lacks immunity protection.

That's what happened in 2017, when an outbreak started in the Somali-American community in Hennepin County, where childhood measles vaccination rates were below 50%. Eventually, the disease spread and 75 were sickened.

Martin said parents with concerns should contact their doctor or clinic.

"It is really important for parents to reach out to their child's health care provider and find out how they can best stay on track with these vaccinations," she said.

Glenn Howatt • 612-673-7192

Twitter: @GlennHowatt