Genuine vaccine injuries are rare. Over the 18-year period from 2006 to 2023, more than 5.3 billion doses of covered vaccines were distributed in the United States, and roughly 1 person per million doses received compensation through the federal vaccine injury program. That ratio puts serious vaccine injury among the least common medical risks most people will encounter, though the specific odds vary depending on the vaccine, the reaction in question, and who’s receiving it.
Side Effects vs. Vaccine Injuries
Most reactions to vaccines are minor, short-lived, and expected. A sore arm, low-grade fever, or fatigue after a shot are normal immune responses, not injuries. The CDC classifies adverse reactions into three tiers: local reactions like redness and swelling (the most common), systemic reactions like fever and body aches (less common), and severe allergic reactions like anaphylaxis (the rarest).
A “vaccine injury” in the legal sense is something more serious. Under the National Childhood Vaccine Injury Act of 1986, the U.S. maintains a Vaccine Injury Table listing specific conditions linked to specific vaccines. To qualify for compensation, an injury generally needs to have lasted more than six months, required hospitalization and surgery, or resulted in death. That’s a high bar, and it filters out the vast majority of uncomfortable but harmless side effects.
Anaphylaxis: The Most Tracked Severe Reaction
Anaphylaxis, a rapid and potentially life-threatening allergic reaction, is the severe outcome people worry about most. Across all vaccines, it occurs at a rate of about 1.31 per million doses. A large study covering more than 25 million vaccine doses identified just 33 confirmed cases of anaphylaxis over three years.
Rates do vary by vaccine type. The MMR vaccine triggered anaphylaxis at about 5.1 per million doses. The chickenpox vaccine came in at roughly 6.9 per million. Influenza vaccines, which account for huge volumes of doses, sat at 1.5 per million. Hepatitis B had zero confirmed cases out of nearly 1.3 million doses in that study period. These are small numbers in absolute terms, and anaphylaxis is treatable when caught quickly, which is why vaccination sites ask you to wait 15 minutes afterward.
Myocarditis After mRNA COVID-19 Vaccines
The most prominent vaccine safety signal in recent years was myocarditis, or inflammation of the heart muscle, following mRNA COVID-19 vaccines. This risk was real but concentrated in a narrow demographic: young males after their second dose.
The highest reported rate was in 16- to 17-year-old males after a second Pfizer dose, at about 75.9 cases per million doses. For 12- to 15-year-old males after a second dose, the rate was roughly 46.4 per million. Among males aged 18 to 24, it was around 38.9 per million second doses. To put that in individual terms, Israeli health data estimated the risk for 12- to 15-year-old boys after a second dose at about 1 in 12,361.
For females in the same age groups, rates were dramatically lower. A 16- to 17-year-old girl’s risk after a second Pfizer dose was about 7.5 per million, roughly one-tenth the rate for boys. For adults over 50 of either sex, rates dropped below 1 per million and blended into the background rate of myocarditis that occurs naturally in the population. Most cases of vaccine-associated myocarditis were mild and resolved with standard care.
Guillain-Barré Syndrome
Guillain-Barré syndrome, a condition where the immune system attacks nerve cells and causes weakness or paralysis, has a long-studied connection to certain vaccines. The clearest historical example is the 1976 swine flu vaccine, which carried a risk of about 1 additional case per 100,000 vaccinated people.
With modern seasonal flu vaccines, the increased risk, when detectable at all, has consistently fallen in the range of 1 to 2 extra cases per million doses. CDC studies also found an elevated GBS risk after the Johnson & Johnson (Janssen) COVID-19 vaccine but not after the Pfizer or Moderna mRNA vaccines.
Blood Clots With Low Platelets (TTS)
Thrombosis with thrombocytopenia syndrome, a condition involving unusual blood clots combined with dangerously low platelet counts, emerged as a rare but serious risk with adenoviral vector COVID-19 vaccines like AstraZeneca and Johnson & Johnson. In Australia, the rate was approximately 2 to 3 per 100,000 people vaccinated with AstraZeneca for those under 60, and about 2 per 100,000 for those 60 and older. This risk was a major factor in the eventual discontinuation of these vaccines in many countries as mRNA alternatives became widely available.
Intussusception After Rotavirus Vaccine
Rotavirus vaccines, given to infants to prevent severe diarrheal illness, carry a small additional risk of intussusception, a condition where part of the intestine folds into itself. The estimated additional risk ranges from about 1 in 20,000 to 1 in 100,000 infants vaccinated. An earlier rotavirus vaccine (RotaShield) was pulled from the market in 1999 because of a higher intussusception rate, and current formulations were redesigned to minimize this risk.
How the U.S. Tracks and Compensates Injuries
The primary early-warning system in the U.S. is the Vaccine Adverse Event Reporting System, or VAERS, which accepts reports from anyone, including patients, parents, and healthcare providers. It’s useful for spotting patterns, but its data can’t prove that a vaccine caused a given problem. Reports may be incomplete, inaccurate, or coincidental. The number of VAERS reports for a given condition is not the same as the number of confirmed vaccine injuries.
More rigorous analysis comes from the Vaccine Safety Datalink, which links vaccination records to medical records across major healthcare systems. This allows researchers to compare rates of health problems in vaccinated and unvaccinated populations and detect whether a vaccine is actually increasing risk beyond what would happen by chance.
Two federal programs handle compensation. The Vaccine Injury Compensation Program (VICP) covers routine childhood and adult vaccines, uses a no-fault legal process, and can pay attorneys’ fees. The Countermeasures Injury Compensation Program (CICP) covers emergency-use vaccines like COVID-19 shots, has a shorter one-year filing deadline, and does not cover legal costs. The VICP is generally considered more favorable to claimants. Between 2006 and 2023, the VICP received 13,778 petitions and compensated 10,027 of them. Many compensated cases are settled as negotiations rather than as determinations that the vaccine definitively caused the injury.
Putting the Numbers in Context
The roughly 1-per-million compensation rate across all vaccines is an average that smooths over real variation. Some vaccines and some populations carry higher specific risks, as the myocarditis data for young males showed. Others, like hepatitis B or the inactivated polio vaccine, have safety profiles so clean that serious reactions are nearly undetectable even in studies covering millions of doses.
What’s consistent across the data is that confirmed, serious vaccine injuries are tracked in cases per million, not cases per thousand or per hundred. For comparison, the background rate of anaphylaxis from any cause in the general population is estimated at 50 to 112 episodes per 100,000 people per year, making vaccine-triggered anaphylaxis a tiny fraction of overall anaphylaxis risk. The diseases these vaccines prevent, by contrast, carry complication rates measured in percentages, not parts per million.