Are COVID-19 vaccines safe in the long term?

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The evidence so far is reassuring, with more than five years of safety data. But rare serious harms are real, and some injuries can last. That does not settle every possible future risk.

Why people believe it

In a 2024 CDC survey, serious or unknown side effects were the concern adults cited most often. These adults had not had a 2023–24 dose. Distrust of government was another reason. The survey had limits in what people reported about themselves and in the share of people who replied. The early evidence also had limits. FDA's initial Pfizer review had a median (middle) follow-up time of two months after dose two. Asking what happened later is reasonable.

“Could illness appear years later?”

EMA reports no evidence that COVID-19 vaccines cause side effects such as cancer in the long term. The initial Pfizer trial review warned that very uncommon reactions could remain undetected. It also warned that reactions needing longer follow-up to detect could remain undetected. WHO's later review draws on more than five years of trial and safety-monitoring data. That is longer observation, not a guarantee covering decades.

“Does it raise the risk of dying?”

A French study followed 22.7 million adults given mRNA vaccines, such as Pfizer or Moderna. It also followed 5.9 million unvaccinated adults. The adults were aged 18–59, with a median follow-up of 45 months. It found no increased four-year risk of death from all causes after Pfizer or Moderna vaccination in that age group. Differences between the groups could affect comparisons. A study of deaths cannot settle every illness that does not cause death.

“Can heart damage last?”

Yes: mRNA vaccines can cause myocarditis, or heart-muscle inflammation. FDA reported that hospitalized patients with myocarditis linked to vaccination commonly still had abnormal findings on heart MRI scans. This was at a median of about five months after vaccination. What those scans mean for future health remains unknown. A French follow-up study looked at hospitalized myocarditis patients aged 12–49. It found that some patients with myocarditis after mRNA vaccination could need care for months after leaving hospital. Lasting effects of an early injury and a new illness beginning years later are separate questions.

“What about other serious injuries?”

Janssen and AstraZeneca vaccines have established links to rare clotting and nerve disorders. The clotting disorder can be fatal. Guillain-Barré syndrome involves nerve damage that can cause weakness or paralysis. Reports of heart inflammation after Novavax have been flagged for investigation. For protein subunit vaccines, precise estimates of vaccine-caused heart-inflammation risk are unavailable. WHO says safety evidence for protein subunit vaccines is more limited than for mRNA vaccines because protein subunit vaccines have been used less.

“Does it affect fertility?”

EMA found at least a reasonable possibility that Pfizer and Moderna cause heavy menstrual bleeding. Most reviewed cases appeared temporary and not serious. WHO says available evidence has not established that vaccination causes infertility, or difficulty having children. That evidence also has not established that vaccination causes persistent changes to periods. These are different outcomes.

Official positions and dates

WHO's 31 July 2026 paper describes a favourable safety profile. It also acknowledges specific harms caused by the vaccines. Its 15 September 2026 Q&A recommends routine vaccination for people at highest risk of severe COVID-19. FDA's 25 June 2025 notice said required studies of longer-term heart effects after myocarditis were underway.

EMA's history of updates to its key-facts page has a latest entry of 8 April 2026. The section on long-term safety has no separate date. It reports no evidence that COVID-19 vaccines cause side effects such as cancer in the long term. CDC's 23 September 2026 guidance describes trial reactions as mostly mild and brief. It also describes continued monitoring of reported fever-related seizures in young children.

What people also ask

What are the potential side effects of the Pfizer COVID vaccine?

Reactions at the injection site and tiredness were common in the trial's subset of vaccinated adults. Across COVID-19 vaccine trials, most symptoms were mild to moderate and went away within one to three days.

Are there long-term effects from the Pfizer COVID vaccine?

Persistent abnormal findings on heart MRI scans have been recorded in hospitalized patients with myocarditis linked to mRNA vaccines. What these findings mean for their future health is uncertain. WHO calls serious or long-lasting side effects extremely rare.

Does Pfizer or Moderna have worse side effects?

A French study using 2021 data estimated extra cases of hospitalized myocarditis in men aged 18–24. Within seven days, it estimated 4.7 extra cases per 100,000 second Pfizer doses. That compares with 17 per 100,000 second Moderna doses within seven days. That comparison concerns this outcome and group, not all side effects. WHO also links gaps of at least six months between mRNA doses with substantially lower myocarditis risk.

What is the mortality risk after the COVID vaccine?

The French four-year study found no increased overall death risk at ages 18–59 after mRNA vaccination. Rare vaccine injuries have been fatal. CDC's May 2023 summary identified nine deaths caused by Janssen vaccination.

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