MMR Vaccines & Seizures: The Fine Print from Health Giants - Insights from CDC & WHO

From Rare Events to Robust Safety Nets: The Story Behind MMR and Seizures

Both the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO) acknowledge that febrile seizures can occur following the administration of the Measles, Mumps, and Rubella (MMR) vaccine.

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CDC

The CDC indicates there is a small increased risk of febrile seizures following MMR vaccination, particularly in the 5 to 12 days post-vaccination window. This risk is higher for the first dose of the vaccine, especially in children aged 12 to 23 months. However, febrile seizures after MMR vaccination are rare, and the risk is considered to be outweighed by the benefits of vaccination, which protects against diseases that can lead to more severe complications, including febrile seizures from the natural infection itself.¹

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WHO

The WHO similarly recognizes that febrile seizures might occur following MMR vaccination but emphasizes that this does not lead to long-term neurological consequences. The WHO, like the CDC, highlights that the benefits of MMR vaccination in preventing measles, mumps, and rubella far outweigh the risks. ²

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Incidence:

• MMR Vaccine: The risk of febrile seizures following the MMR vaccine is estimated to be approximately 1 in 3,000 to 4,000 doses. This statistic is derived from large-scale studies and vaccine safety surveillance data. The seizure is usually a febrile (fever-related) seizure, which is not uncommon in young children during any fever, whether vaccine-related or due to infection.³⁴

• MMRV Vaccine: When the varicella (chickenpox) vaccine is combined with MMR to form the MMRV vaccine, the risk of febrile seizures is slightly higher, especially following the first dose. This increased risk has been observed to be about twice that of the separate MMR and varicella vaccines given at the same visit. It's roughly around 1 in about 1,500 to 2,000 doses. This has led to recommendations in some guidelines to administer MMR and varicella vaccines separately rather than combined, especially for the first dose, to minimize this risk.⁵⁶

Timing:

• Febrile seizures following MMR/MMRV vaccination typically occur within 7 to 14 days after vaccination. This timing corresponds with the peak in fever occurrence post-vaccination, which is when the immune system is most active in responding to the vaccine.⁷

Risk Factors:

• Personal or Family History of Seizures: Children with a history of febrile seizures or epilepsy, or those with a family history of such conditions, might have an increased risk. However, this does not generally contraindicate vaccination, as the benefits of preventing measles, mumps, rubella, and potentially varicella usually outweigh the risks. A healthcare provider might decide differently based on the specific health history of the child.⁸

• Age: The risk is higher in younger children, particularly between 12 to 23 months, which is the recommended age for the first MMR dose. Older children tend to have a lower risk.⁹

Long-term Effects:

• Febrile seizures, whether caused by vaccination or other fever-inducing conditions, are generally benign. They do not cause long-term brain damage, intellectual disability, or increase the risk of epilepsy. Most children recover without any issues, and the likelihood of developing epilepsy is not significantly increased following a febrile seizure after vaccination compared to febrile seizures from other causes.¹⁰

Vaccine Safety Monitoring:

• VAERS (Vaccine Adverse Event Reporting System): In the U.S., VAERS is a national vaccine safety surveillance program co-managed by the CDC and the FDA. While it captures all adverse events reported after vaccination, it's important to note that a report doesn't confirm that the vaccine caused the event; it's a tool for spotting patterns or signals.¹¹

• Other Systems: Globally, the WHO's Global Advisory Committee on Vaccine Safety (GACVS) reviews data from various surveillance systems.¹² In Europe, there's EudraVigilance¹³; in Canada, CAEFISS (Canadian Adverse Events Following Immunization Surveillance System); and many countries have their own systems.¹⁴

• Post-Marketing Surveillance: Beyond initial clinical trials, post-marketing surveillance continues to monitor vaccine safety, looking for rare side effects that might not have been detected in smaller study populations.¹⁵

• Research: Ongoing research and epidemiological studies help refine our understanding of vaccine risks and benefits, sometimes leading to adjustments in vaccine schedules or recommendations (like the separate administration of MMR and varicella vaccines versus MMRV for the first dose).

1. https://www.cdc.gov/vaccine-safety/about/febrile-seizures.html

2. https://pmc.ncbi.nlm.nih.gov/articles/PMC8607336/

3. https://www.cdc.gov/vaccinesafety/concerns/febrile-seizures.html

4. https://pubmed.ncbi.nlm.nih.gov/24917990/

5. https://www.cdc.gov/vaccines/vpd/mmr/hcp/recommendations.html#mmrv

6. https://pubmed.ncbi.nlm.nih.gov/20587674/

7. https://www.cdc.gov/vaccine-safety-systems/vsd/?CDC_AAref_Val=https://www.cdc.gov/vaccinesafety/ensuringsafety/monitoring/vsd/index.html

8. https://pubmed.ncbi.nlm.nih.gov/20587674/

9. https://www.cdc.gov/vaccine-safety/about/febrile-seizures.html?CDC_AAref_Val=https://www.cdc.gov/vaccinesafety/concerns/febrile-seizures.html

10. https://publications.aap.org/patiented/article-abstract/doi/10.1542/peo_document038/80001/Febrile-Seizures-and-Your-Child?redirectedFrom=fulltext

11. https://vaers.hhs.gov/

12. https://www.who.int/teams/regulation-prequalification/regulation-and-safety/pharmacovigilance/networks/vaccine-safety-net/vsn-members/global-advisory-committee-on-vaccine-safety

13. https://www.ema.europa.eu/en/human-regulatory-overview/research-development/pharmacovigilance-research-development/eudravigilance

14. https://www.canada.ca/en/public-health/services/immunization/canadian-adverse-events-following-immunization-surveillance-system-caefiss.html

15. https://pmc.ncbi.nlm.nih.gov/articles/PMC6500454/