Fact check: What percent of people get seizures after vaccines

1. Why this question matters now — putting seizure risk into plain numbers and context

Public discussion often asks what percent of people get seizures after vaccines; the clearest data refer to febrile seizures in young children, not chronic epilepsy in the general population. A December 23, 2024 review reports that up to 5% of young children will have a febrile seizure at some time, but that the incremental risk attributable to vaccination is much smaller, quantified at no more than about 30 febrile seizures per 100,000 children vaccinated when particular vaccines are co-administered ^[1]. That framing matters because the baseline incidence of febrile seizures from common childhood infections is higher, so vaccines prevent many fever-producing illnesses and thereby prevent some seizures overall. The key takeaway: the background risk of febrile seizures is orders of magnitude larger than the vaccine-attributable increase, and most febrile seizures are brief and resolve without long-term consequences ^[1].

2. The strongest data point — combined vaccine schedules and the 30-per-100,000 figure

Epidemiologic analyses summarized from a Pediatrics study originally published in 2016 and reiterated in later summaries found that co-administration of influenza, DTaP, and pneumococcal conjugate (PCV) vaccines can increase the risk of febrile seizures to roughly 30 per 100,000 immunized children, compared with lower rates when those vaccines are given separately ^[2]. The authors and public-health reviewers concluded that the small increased short-term risk does not outweigh the benefits of co-administration, which include improved vaccine uptake and earlier protection against serious infections. This data point is the most cited quantification of vaccine-associated febrile seizure risk and is used by health authorities when weighing scheduling trade-offs ^[2].

3. What the literature does and does not show — limits and gaps to bear in mind

A 2025 book chapter reviewing vaccination as a risk factor for febrile seizures reiterates that vaccines can be a risk factor but does not provide a single population-wide percentage, reflecting heterogeneity by vaccine type, age, and co-administration practices ^[3]. The evidence is strongest for short-term, fever-associated seizures in infants and toddlers, and much weaker or absent for claims that vaccines cause chronic seizure disorders like epilepsy. Data limitations include variable surveillance methods, differing vaccine schedules across countries, and rare-event statistics that make precise percent estimates difficult for older children and adults. Thus the literature provides a reliable small absolute risk estimate for specific pediatric scenarios but not a simple single-percent answer for all people or all vaccines ^[3].

4. Public-health tradeoffs and expert conclusions — weighing benefits against the small risk

Authors and public-health reviewers repeatedly state that the benefits of vaccinating on schedule exceed the small risk of febrile seizures, citing fewer clinic visits, higher coverage, and prevention of serious disease as key factors supporting combined vaccination strategies ^[2]. Because febrile seizures are usually brief and not linked to long-term neurological damage, the clinical harms from the small excess risk are limited compared with the morbidity and mortality prevented by vaccines. That assessment guides official recommendations: avoid interpreting the small rate of vaccine-associated febrile seizures as evidence against routine immunization, and consider individual risk factors only in consultation with clinicians ^{[2] [1]}.

5. Where debate and agendas appear — read the data, not the rhetoric

Discourse around vaccine risks can be shaped by advocacy groups or selective citation of studies; the peer-reviewed epidemiologic literature consistently quantifies vaccine-linked febrile seizures as a rare, short-term event while emphasizing net public-health benefit ^{[2] [1]}. The 2024 and 2025 reviews consolidate evidence and caution against extrapolating pediatric febrile-seizure risks to claims that vaccines commonly cause long-term seizures or epilepsy ^{[1] [3]}. For decision-making, the relevant facts are the absolute rates (about 30 per 100,000 in specific co-administration contexts), the baseline febrile-seizure incidence (up to 5% lifetime in young children), and the net reduction in disease burden achieved by vaccination; those facts should guide clinicians and parents more than alarmist headlines ^{[1] [2] [3]}.