MMR+V vs. MMRV: Understanding Vaccination Choices

Most children receive the MMR+V vaccine because it has been preferred over the single shot option based on historical data. The MMRV vaccine was approved by the Food and Drug Administration in 2005, but after some time, it became apparent that there was a slight increase in the risk of febrile seizures when administered as the initial dose for toddlers aged 12 to 15 months. However, no increased risk has been seen with the second recommended dose given between 4 to 6 years.

The risk increase is small—data indicates there were 7 to 8.5 seizure cases per 10,000 first-dose MMRV vaccinations, compared to 3.2 to 4.2 in 10,000 first-dose MMR + V vaccinations. This translates to about one additional febrile seizure for every 2,300 to 2,600 children vaccinated. While alarming for parents, febrile seizures are generally harmless. They occur alongside fevers caused by various illnesses like the flu or ear infections. Most children recover completely without any long-term consequences. It’s estimated that by age 5, around 5 percent of all children will have experienced a febrile seizure at some point.

Nonetheless, due to the relative increase in risk with MMRV, the Advisory Committee on Immunization Practices (ACIP) in 2009 reviewed the data and decided to recommend MMR+V over MMRV. Still, MMRV was recognized as safe and effective, remaining available for parents to discuss with their healthcare providers. Experts have not observed any new data that would challenge this perspective since that decision.

Vulnerable Toddlers

From 2015 to 2025, the usage of MMRV among children in King County remained consistent at 15 percent over that decade, despite the recommendations. This percentage seemed to correspond with specific demographic characteristics: children who received the MMRV as their first dose were notably more likely to belong to minority racial and ethnic groups. Furthermore, a larger number of these children were receiving a “catch-up dose” after the recommended age of 12 to 15 months, typically getting vaccinated between 16 and 47 months. Additionally, children receiving MMRV were found to be over three times more likely to qualify for a federal program that provides free vaccines to low-income families, and nearly four times more likely to get vaccinated at safety-net clinics.