Can the flu shot cause the flu? Is it even effective?

Is the flu shot a vaccine?
Yes. The flu shot is a vaccine that helps your immune system recognize and fight the influenza virus. It reduces the risk of getting the flu and can help prevent serious illness if you do become infected.

Was the flu shot well studied? Was there a placebo-controlled trial?
Yes. The flu vaccine has been studied for more than 70 years. It was evaluated in randomized, placebo-controlled clinical trials and continues to be monitored through ongoing safety and effectiveness studies.

Are there serious adverse events in kids who receive the flu shot?
Serious reactions to the flu shot are very rare. Most side effects are mild and temporary, such as soreness at the injection site, fatigue or a low-grade fever. These symptoms are signs that the immune system is responding to the vaccine, not signs of the flu itself.

Does the flu shot contain dangerous toxic adjuvants/ingredients (e.g., aluminum, mercury, formaldehyde)?
The ingredients used in flu vaccines have been extensively studied and are present in very small amounts. Historically, some flu vaccines contained thimerosal, a preservative that includes a form of mercury called ethylmercury, which is different from the more harmful methylmercury that can accumulate in the body. Out of an abundance of caution, thimerosal was removed or reduced to trace amounts in routine childhood vaccines more than two decades ago, even though studies did not show evidence of harm from its use in vaccines. Today, most flu vaccines used in children are thimerosal-free. The ingredients that remain serve important purposes, such as keeping the vaccine sterile, stable and effective.

Is there an FDA warning for the flu shot?
The flu shot does not carry an FDA black box warning. Like all vaccines and medications, it includes a package insert that describes potential side effects, risks and safety information.

Do flu shots cause shedding?
Flu shots use inactivated virus and do not cause viral shedding. You cannot spread the flu to someone else because you received a flu shot.

Can the flu shot cause the flu?
The flu shot cannot cause the flu because it contains an inactivated virus that cannot cause infection.

Does the flu shot actually prevent the flu?
Yes, the flu shot helps prevent the flu. Protection is generally strongest when the vaccine closely matches the circulating flu strains. But no vaccine prevents every infection for all people.

Some years, the flu shot isn’t as effective as others; why is that?
Scientists must predict which flu strains will circulate months before flu season begins. Some years the vaccine is a closer match than others, which is why effectiveness can vary from season to season.

If the flu shot isn’t 100% effective, is it still worth getting?
Yes. Even when the flu shot doesn’t completely prevent infection, it can reduce the risk of severe illness, pneumonia, hospitalization and death. Getting vaccinated is safer than getting the flu itself.

Are people who get the flu shot more likely to get a non-flu infection (through pathogenic priming)?
There is no evidence that receiving a flu vaccine makes people more likely to develop other infections or weakens their immune system.

What is the risk if a child contracts the flu? Are kids at higher risk than adults?
Most healthy children recover from the flu. However, children under age 5, especially those younger than 2, are at higher risk of flu-related complications. These can include pneumonia, bacterial infections, dehydration, hospitalization and, in severe cases, intensive care admission.

Does the flu shot actually prevent hospitalization or death? Are there high-quality studies that show this?
Yes. Even when vaccinated people get the flu, their illness is often less severe. Recent research found the flu shot reduces the risk of children and teens dying from flu by 80%. A separate analysis found it prevented nearly 15,000 hospitalizations and 245 deaths in children and teens in the 2024-2025 season.

Is natural immunity better than the flu shot?
Natural immunity can develop after a flu infection, but it comes with the risk of severe illness and complications. The flu vaccine helps your body build protection without exposing you to those risks.

Should every kid get the flu shot, or only high-risk groups?
The American Academy of Pediatrics recommends annual flu vaccination for everyone 6 months and older who does not have a medical reason to avoid it.

Can flu shots cause febrile seizures?
Rarely, a fever after vaccination can trigger a febrile seizure in a young child, but these seizures generally do not cause lasting harm. Because the flu can also cause high fevers and febrile seizures, vaccination helps protect against a greater risk.

I see a lot of stories about unvaccinated kids being healthier than vaccinated kids, or kids who’ve had vaccine injuries. How do I know what to believe?
There’s a lot of information – and misinformation – online. When evaluating health claims, look for evidence from trusted medical organizations and scientific studies. If you have questions about what’s best for your child, talk with your pediatrician.

Can natural alternatives like vitamin D and garlic help prevent the flu? Can I just use those instead?
Good nutrition, adequate sleep and handwashing all support overall health, but none has been shown to provide the same protection against influenza as vaccination. The flu vaccine remains the most effective way to reduce the risk of flu-related illness and complications.