Helen Branswell , 2026-01-02 16:00:00
Babies who don’t get their first round of vaccines on time at 2 months of age are much less likely to get vaccinated against measles, mumps, and rubella by age 2, according to a new study that suggests pediatricians may have a narrow window in which to persuade parents to follow the recommended childhood vaccination schedule.
The study, published Friday in JAMA Network Open, reports that in the post-Covid-19 pandemic period, babies who didn’t get their shots on time at 2 months — the age at which the Centers for Disease Control and Prevention recommends babies get vaccines against a host of diseases — were more than seven times more likely not to receive their first measles, mumps, and rubella (MMR) shot by age 2, which is months later than when that shot is supposed to be given. Babies are supposed to get their first MMR shot between 12 months and 15 months of age, with a second sometime between the ages of 4 and 6.
“There’s evidence from this study that very early vaccination delays lead to later vaccination delays and even missed vaccination for measles,” said Nina Masters, an epidemiologist who is the lead author of the paper. “This shows that hesitancy is really starting early and has a long arc.”
“And as we look at a really bad measles year, it’s really important to do whatever we can to try to increase measles vaccination coverage.”
The CDC reported this week that as of Dec. 30, the U.S. had registered 2,065 confirmed measles cases in 2025, the most in a single year in more than three decades. There are concerns that some of the current cases are linked to an outbreak that was first detected in West Texas last January — a fact that, if confirmed, would set the country on the path to losing its measles elimination status sometime early this year.
The study is based on electronic health records data maintained by Truveta, a health care data analytics company owned and governed by 30 health systems. Truveta’s data pool contains health care usage information for about 120 million individuals — about a third of the country.
Masters is a senior applied research scientist at Truveta. She and her co-authors studied de-identified health care data for about 322,000 children born between 2017 and 2023 who received regular care from a health care system in the Truveta network, looking at vaccination patterns within their first two years of life.
The finding that children whose earliest shots are delayed are likely to get subsequent shots later than recommended — or not at all — isn’t new; previous studies have also shown this.
“A strong predictor of future vaccination is having received any vaccine in the past,” said Noel Brewer, a professor of health behavior at the University of North Carolina. Brewer was a member of the CDC’s vaccine advisory panel until health secretary Robert F. Kennedy Jr. fired the entire committee last June and appointed people who share his vaccine skepticism to it in their place.
But the period studied in the paper ranged from 2018 to 2024, which allowed the researchers to look for changes that might have happened after the Covid-19 pandemic began. Declines in vaccination rates since the pandemic have been associated with an increase in distrust of public health authorities and resentment over Covid containment measures.
Over the total period, 78.4% of the children received their first MMR shot on time, 13.9% received it late, 1% received it early, and 6.7% did not receive it by 2 years of age.
But the researchers did indeed see a dip in the rate of children who received their first dose of MMR vaccine on time. It declined by three percentage points between 2021 and 2024, Masters noted. “It’s a pretty substantial drop in three years.”
Notably, the percentage of children who received the MMR shot late remained relatively constant during the period of the study. What changed was the percentage of children who hadn’t received a first MMR dose by age 2. That figure rose from 5.3% in 2020 to 7.7% in 2024. “It wasn’t that more people were delaying. It was that more people were not getting the MMR vaccine [for their babies] at all by 2 years,” she said.
The biggest indicator of whether children would receive their first dose of MMR vaccine on time came very early in the vaccination process — whether babies received those vaccines that were recommended at 2 months old on time.
Vaccination against multiple pathogens begins with a visit to the pediatrician at 2 months of age, when the CDC recommends babies be immunized against hepatitis B, rotavirus, diphtheria, tetanus, pertussis, polio, Haemophilus influenzae type b, and pneumococcal disease. (This doesn’t involve eight separate inoculations; when possible, pediatricians use multivalent vaccines that protect against five or six of these diseases with a single shot.)
Masters said that the findings suggest pediatricians should begin talking with parents about the importance of vaccinating — and vaccinating on time — before the appointment at 2 months.
“The three biggest influences on vaccination are past vaccine receipt, intending to vaccinate, and a doctor’s recommendation,” said Brewer, who was not involved in the study. “The most promising avenue for intervention is a doctor’s recommendation.”
The American Academy of Pediatrics recommends frequent contact between pediatricians and babies early in the children’s lives. Those visits include within the first week, at 1 month and 2 months of age, and again at 4 months, 6 months, and 9 months.
Studies show that the best way to persuade parents to vaccinate their children is to have them receive a recommendation from a trusted medical practitioner. But with multiple shots scheduled for the 2-month visit, there isn’t a lot of time for pediatricians to establish a relationship of trust with the parents of a new patient, Masters said.
“So it does create this window of opportunity that’s quite short and puts the onus, I think, on those pediatricians really to talk about vaccines early, build trust early, build education [and] familiarity right off the bat. Don’t wait for that 2-month visit, when the parent might decline or delay, but really do it right away,” she said.
Adding to that challenge is the fact that many babies do not see pediatricians on that recommended schedule. The study found that within the cohort studied, just under half the babies saw their medical providers according to the AAP’s schedule. And these were babies with a medical home, the study noted. They had a pediatrician. Their parents had health insurance. The numbers were probably lower still, Masters said, among children whose parents didn’t have insurance or who hadn’t managed to register with a pediatric practice.
“I think it’s conservative,” she said of the findings. “I think if we had a way to look at the parents that aren’t bringing their children in, that aren’t vaccinating their children, that don’t have a medical home — which we don’t have the ability to do — we would likely see lower coverage, lower timeliness, just in general lower opportunities for intervention to get children back on track once they fall off the schedule.”
Brewer said most children receive some vaccines, but a willingness on the part of parents to deviate from the recommended schedule for some shots is typically a sign of things to come.
“People who skip one vaccine are more likely to skip other vaccines,” he said. “Only around 2% of people will never get any vaccines. So most people get most vaccines. But the people who don’t get some vaccines are also less likely to get others.”
Masters noted the paper does not capture any impact of the changes to vaccination policy that have occurred since Kennedy — a longtime proponent of disproven claims about the safety of vaccines — was named as the country’s top health official.
Among those changes: an early December decision by the CDC’s vaccine advisory committee to jettison a 30-plus year recommendation that all babies be offered hepatitis B vaccination within 24 hours of birth. It now recommends at-birth vaccination only for babies whose mothers tested positive for hepatitis B during pregnancy or whose test status is unknown. Other babies should begin hepatitis B vaccination — if their parents want it — at 2 months of age, the CDC now recommends.
Masters said she and her colleagues are considering trying to look at the implications of the hepatitis B vaccine changes.
