The question of whether COVID-19 vaccines can lead to seizures is a significant safety concern that has been thoroughly investigated by health authorities worldwide. Understanding the relationship between vaccination and neurological events requires a careful review of large-scale surveillance data and an examination of the underlying biological processes. The robust systems in place for tracking vaccine side effects allow researchers to provide clear conclusions regarding the incidence and potential causes of seizures reported following immunization.
The Data on Seizures and COVID Vaccines
Extensive data from global surveillance systems and epidemiological studies show that seizures following COVID-19 vaccination are exceedingly rare events. A meta-analysis of multiple randomized, placebo-controlled clinical trials, including tens of thousands of participants, found no statistically significant difference in the risk of new-onset seizures between vaccinated individuals and those who received a placebo. This finding applied across different vaccine types, including messenger RNA (mRNA), viral vector, and inactivated virus platforms. Independent studies consistently demonstrate there is no causal association between the vaccine components and the onset of generalized seizures.
While generalized seizures are not associated with the vaccine, a small safety signal for febrile seizures was identified in very young children. Data from the Vaccine Safety Datalink (VSD) indicated a slight, temporary increase in the risk of febrile seizures in children aged two to five years, occurring most often within one day after receiving the Moderna mRNA vaccine. Febrile seizures are convulsions triggered by a fever, and the absolute risk remains very low, estimated at approximately 3.22 cases per 100,000 doses in that age group. For the general population, the estimated incidence rate of new-onset seizures following COVID-19 vaccination is around 3.19 per 100,000 persons per year.
Individuals with pre-existing epilepsy may experience a temporary increase in seizure frequency following vaccination, often within the first month. This temporary change is often attributed to the fluctuating nature of the condition, as most people with epilepsy report no change in their seizure control. The frequency of neurological complications, including seizures, is substantially higher following a COVID-19 infection than it is after receiving the vaccine.
Biological Plausibility and Immune Response
The connection between vaccination and seizures is explained by the body’s expected immune response rather than a direct toxic effect of the vaccine ingredients. Vaccines stimulate the immune system, which commonly results in temporary side effects, such as fever. Fever is a recognized trigger for seizures, particularly in children predisposed to febrile seizures. This phenomenon is observed with many childhood vaccines and is not unique to the COVID-19 immunization.
It is important to distinguish between the vaccine acting as a trigger and the vaccine being the cause of the seizure. The vaccine itself does not create the neurological condition; rather, the fever it induces can lower the seizure threshold in susceptible individuals. The body’s inflammatory reaction to the vaccine is temporary and typically resolves within one to two days. This temporary inflammation is what generates the fever that can then trigger a febrile seizure in a small, at-risk subset of the population.
Rarely, the immune activation stimulated by a vaccine could theoretically lead to an immune-mediated neurological event, but this is an extremely infrequent possibility. The scientific consensus is that the vaccine components, such as the mRNA or viral vector, do not cross the blood-brain barrier in a way that would directly disrupt neuronal activity and cause a generalized seizure. Rigorous studies have focused on this distinction, confirming that the neurological risk is related to the transient immune response and not a direct neurotoxic effect.
How Vaccine Safety is Monitored
The data confirming the rarity of seizures post-vaccination are collected and analyzed through several robust safety monitoring systems established by health agencies. In the United States, the Vaccine Adverse Event Reporting System (VAERS) is a primary national system co-managed by the Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA). VAERS is a passive surveillance system that collects reports of any health problem that occurs after vaccination, submitted by healthcare providers, manufacturers, and the public.
Because VAERS accepts reports regardless of whether a vaccine caused the event, its data can only identify potential safety signals, not establish a cause-and-effect relationship. The system may show a clustering of reported events, such as seizures, which then prompts further investigation. These preliminary signals must be verified through active surveillance systems to determine true causality.
One such active monitoring system is the Vaccine Safety Datalink (VSD), which uses electronic health record data from participating healthcare organizations to conduct rapid, large-scale epidemiological studies. The VSD allows researchers to compare the rate of adverse events, like seizures, in vaccinated people to the expected background rate in the general population. This rigorous comparison confirmed and contextualized the very low rate of febrile seizures in young children. The continuous, multi-layered monitoring that uses both passive reporting and active data analysis ensures that any potential safety issue is quickly detected and thoroughly evaluated.