Late Infant Vaccinations Linked to Children not Receiving MMR

The number of children who are unvaccinated against measles has increased since the COVID-19 pandemic, with some counted among the cases and related deaths that spiked last year, 25 years after the viral illness was declared extinct in the US.

A recent investigation of possible factors for children not receiving measles, mumps, rubella (MMR) vaccine by the age of 2 has found an association with delayed or missed standard infant vaccinations at 2- and 4- months.¹

"This finding highlights very early opportunities for intervention to address vaccine delay and potentially get children back on track," indicate Nina Masters, PhD, MPH, and colleagues at Truveta Research, Truveta Inc, Bellevue, WA.

The investigators accessed electronic health records for 321,743 children born from 2017 to 2023 with regular access to care, from the Truveta database of multiple US health systems comprising over 120 million anonymized patient records from over 900 hospitals and 20,000 clinics. The records included child visits to clinics at 0 to 2 months, 3 to 11 months, 12 to 21 months and 22 to 25 months.

In addition to demographic data, the investigation ascertained receipt of the 2- and 4-month vaccine series (Hib, DTaP, PCV, IPV, and rotavirus), and created composite timeliness indicators of appropriate vaccination at each age period.The investigators found that 157,427 (48.9%) children had adhered to the American Academy of Pediatrics (AAP) recommended well child visit schedule in the first 2 years of life.

The majority of the children (78.4%) had received the MMR vaccine on time, with 1% receiving it early. The vaccine was received late by 13%, however, and had not been received by 6.7% (21,669) children by 2 years of age. The investigators noted that the post-2021 trend of decrease in timely MMR vaccination (3% decrease from 2021 to 2024) coincided with an increase in the proportion of children having no MMR at 2 years.

Masters and colleagues reported that the strongest factor associated with not receiving any MMR vaccination by 2 years of age was late 2-month and 4-month vaccinations (adjusted OR [AOR] 6.96 [95% CI, 6.60-7.34] and 6.16 [5.84-6.50], respectively).Their analyses also included determinations that male children were "slightly" more likely to be unvaccinated (AOR 1.12 [1.07-1.16]), as were children living in rural areas (AOR 1.09 [1.03-1.15]).

Since the pandemic, the investigators report, children who received their 2-month vaccinations on time had almost 7 times higher odds of receiving the MMR vaccine by 2 years of age, and 2.5 times higher odds of receiving the MMR vaccine on time compared with those who did not.These findings underscore the importance of clinicians encouraging parents to adhere to vaccination schedules, they emphasize.

"Research has shown that clinician conversation style with parents has a strong effect on vaccine uptake at a pediatric visit," Masters and colleagues point out. "Specifically, the use of presumptive conversation styles around vaccine (ie, 'your child is getting 2 shots today') is associated with much higher vaccine uptake (over 17-fold higher) than participatory conversations (ie, 'do you want to get vaccines for your child today?')."²

References

1. Masters NB, Goodwin Cartwright BM, Rodriguez PJ, et al. Delayed or absent first dose of measles, mumps, and rubella vaccination. JAMA Netw Open. 2026; 9(1):e2551814. doi:10.1001/jamanetworkopen.2025.51814.

2. Opel DJ, Heritage J, Taylor JA, et al. The architecture of provider-parent vaccine discussions at health supervision visits. Pediatrics. 2013;132(6):1037-1046.