Delayed or Absent First Dose of Measles, Mumps, and Rubella Vaccination

Area of Science:

• Pediatric infectious disease epidemiology
• Public health surveillance
• Vaccine-preventable diseases

Background:

• Measles cases in the US are at their highest since 2000, with declining vaccination coverage.
• Factors influencing delayed or missed measles, mumps, and rubella (MMR) vaccinations post-COVID-19 pandemic require exploration.

Purpose of the Study:

• To analyze MMR vaccination coverage and trends.
• To identify factors associated with delayed or missed MMR vaccination by age two.

Main Methods:

• A cohort study followed 321,743 children for 24 months using electronic health records from US healthcare systems (January 2018 - April 2025).
• Vaccination outcomes were assessed against the American Academy of Pediatrics well-child visit schedule.
• Mixed-effect logistic regression modeled associations with sociodemographic factors and early vaccine receipt, stratified by pre- and post-COVID-19 eligibility.

Main Results:

• Overall, 78.4% of children received their first MMR vaccine on time, with coverage fluctuating between 2018-2024.
• A significant increase in the proportion of unvaccinated children by age two was observed post-COVID-19.
• Late administration of 2-month (aOR, 6.96) and 4-month (aOR, 6.16) vaccines were strongly associated with no MMR vaccination by age two.

Conclusions:

• Despite most children receiving timely MMR vaccination, a concerning rise in unvaccinated individuals by age two has emerged since the COVID-19 pandemic.
• Early-life vaccination timeliness, particularly for 2- and 4-month immunizations, is critical for ensuring complete MMR vaccination.
• Targeted interventions focusing on timely early childhood immunizations can improve overall MMR vaccine uptake.