The updated COVID-19 vaccines have a strong safety record, backed by more than four years of real-world monitoring across billions of doses worldwide. Common side effects are mild and short-lived, while serious reactions are exceptionally rare, occurring in fewer than 1 in 200,000 vaccinated people. Here’s what the evidence actually shows.
What’s in the Current Vaccines
The FDA updates the COVID vaccine formula annually, similar to the flu shot, to keep pace with circulating virus strains. For the 2025-2026 season, the recommended vaccines target a JN.1-lineage strain (specifically LP.8.1), which more closely matches the versions of the virus spreading now. Both mRNA vaccines (Pfizer and Moderna) and the protein-based Novavax option are available, giving you a choice if you prefer one technology over another.
Each updated formula goes through safety review before authorization. The FDA evaluates clinical data, manufacturing quality, and real-world safety signals from previous versions before clearing a new formulation. The underlying vaccine platforms have not changed, so the extensive safety data from earlier versions still applies.
Common Side Effects and How Long They Last
Most people experience mild, predictable reactions that signal the immune system is responding. The most frequently reported side effects include soreness at the injection site, fatigue, headache, muscle pain, and fever. These typically show up within a day of vaccination and resolve within a few hours to a few days. They’re essentially the same side effects reported since the first COVID vaccines rolled out in 2020.
Pregnant women report the same side effect profile as non-pregnant women. One thing worth noting: fever during pregnancy, regardless of the cause, is associated with potential complications. If you develop a fever after vaccination while pregnant, managing it with a fever reducer is a reasonable step to discuss with your provider beforehand.
Rare but Serious Reactions
Two serious side effects have been clearly identified through years of surveillance: anaphylaxis (a severe allergic reaction) and myocarditis or pericarditis (inflammation of the heart muscle or its surrounding lining).
Anaphylaxis occurs at a rate of roughly 5 per million doses for both Pfizer and Moderna vaccines. That’s about 1 in 200,000. Symptoms usually appear within minutes to hours after vaccination, which is why you’re asked to wait 15 minutes at the vaccination site. Anaphylaxis is treatable when caught quickly, and vaccination sites are equipped to handle it.
Myocarditis drew significant attention early in the vaccine rollout, and the data is now detailed enough to understand who’s most affected. The highest rates were seen in teenage boys and young men after their second mRNA dose: roughly 106 cases per million second doses in males aged 16 to 17, and about 56 per million in males aged 18 to 24. For young females, the rate was far lower, around 6 per million. Symptoms typically appear within seven days of vaccination, and most cases are mild, with patients generally improving within a few weeks.
For the Novavax protein-based vaccine, the FDA’s review of adverse event reports found no deaths attributed to the vaccine after individual case review. Myocarditis and anaphylaxis are listed as identified risks for Novavax as well, though at similarly rare frequencies.
How Vaccine Risks Compare to Infection Risks
Context matters when evaluating these numbers. A systematic review and meta-analysis found that the risk of myocarditis after a COVID-19 infection is approximately 42 times higher than the risk after vaccination. An analysis of over 42 million vaccinations in England reached a similar conclusion: the risk of hospital admission or death from myocarditis was greater after COVID infection than after vaccination. In other words, the condition people worry about most from the vaccine is far more likely to result from the virus itself.
How Safety Is Monitored
COVID-19 vaccines are among the most closely watched medical products in history. Multiple overlapping systems track safety in the U.S. alone. VAERS (the Vaccine Adverse Event Reporting System) collects reports from healthcare providers and the public. The Vaccine Safety Datalink pulls data from large healthcare systems to compare outcomes in vaccinated and unvaccinated populations. The v-safe program allowed vaccinated individuals to report symptoms directly through their phones.
These systems don’t just collect data passively. The FDA and CDC actively analyze report counts, compare current trends to historical baselines, and review individual serious reports. This layered approach is how myocarditis and anaphylaxis were identified as rare risks in the first place, and it’s how regulators confirmed those risks remain low across updated formulations. Each new version of the vaccine undergoes this same ongoing scrutiny.
Safety During Pregnancy
Studies involving more than a million pregnant women worldwide have found no increased risk of miscarriage, preterm delivery, stillbirth, or birth defects associated with COVID-19 vaccination. Vaccination before and during pregnancy produced similar safety outcomes to those seen in non-pregnant populations. The CDC continues to recommend COVID vaccination for people who are pregnant or breastfeeding.
Who Should Not Get the Vaccine
There is one absolute contraindication: if you’ve had a severe allergic reaction (such as anaphylaxis) to a previous dose or to a component of a specific COVID-19 vaccine, you should not receive that same vaccine type again. You may, however, be able to receive the alternate type. For example, if you had a reaction to an mRNA vaccine, the protein-based Novavax may be an option.
People with a history of mild allergic reactions to other vaccines or medications are generally still candidates for COVID vaccination but may be monitored for a longer observation period afterward. If you’ve had myocarditis after a previous COVID vaccine dose, that’s a conversation worth having with your doctor before getting another one.