COVID-19 hasn’t gone away. Just when you think you’ve got the latest guidance down, along come new variants, booster recommendations and questions about side effects. This can make it challenging to keep up with and leave you wondering if the COVID-19 vaccine is really that effective at preventing infection.
Brian Curtis, MD, vice president, chief medical officer, OSF Medical Group, helps cut through the confusion and offers updated, clear and science-backed answers so you can feel confident that getting the COVID-19 vaccine is still one of the smartest steps you can take to prevent infection.
Does the COVID-19 vaccine prevent infection?
Yes, COVID-19 vaccines are highly effective at reducing your risk of infection. While breakthrough infections (getting COVID-19 after being vaccinated) can still happen, vaccinated people experience milder symptoms and recover more quickly than those who are unvaccinated.
People at higher risk for COVID-19, including older adults or those with underlying health conditions, can experience more severe symptoms if infected. This makes getting the COVID-19 vaccine even more important.
“No vaccine prevents every infection,” said Dr. Curtis. “The real benefit of the COVID-19 vaccine is significantly lowering your risk for severe symptoms and keeping you out of the hospital.”
How soon after having COVID-19 can I be vaccinated?
If you’ve tested positive for COVID-19, the Centers for Disease Control (CDC) says you may wait up to three months before you get the vaccine.
Getting the COVID-19 vaccine after you’ve received a positive test result can make the side effects stronger. It can also make the vaccine less effective since your body can’t fight the virus and build vaccine protection at the same time.
“No vaccine works as well if your body is already fighting off an active infection,” said Dr. Curtis. “That’s why we recommend waiting until you’ve fully recovered, and why it’s a good idea to get your COVID-19 shot early in the season – ideally in September or October – before cases start to rise.”
How long does it take to be fully protected after getting the COVID-19 vaccine?
After a COVID-19 vaccine or booster, it typically takes about two weeks for your body to build full protection. During that time, and even after you are fully protected, you may want to take steps to avoid getting sick.
“Things like washing your hands regularly and avoiding close contact with people who are sick are always a good idea during sick season,” said Dr. Curtis.
COVID-19 Vaccine Side Effects: What to Expect
Like any vaccine, COVID-19 shots can cause side effects. Most are mild and short-lived and mean your body is building immunity. The most common COVID-19 vaccine side effects include:
- Sore arm where the shot was given
- Tiredness or fatigue
- Headache
- Muscle aches
- Nausea or diarrhea
- Low-grade fever or chills
These side effects typically last a day or two and resolve on their own.
“If you do experience side effects, simple steps like resting, staying hydrated and using over-the-counter pain relievers can make a big difference,” said Dr. Curtis. “This can give your body the break it needs to build the best protection.”
Both the Moderna and Pfizer COVID-19 vaccines come with similar side effects. For some people, Moderna may trigger slightly stronger side effects after the second dose compared to Pfizer.
Uncommon COVID-19 Vaccine Side Effects
Serious side effects to the COVID-19 vaccine are very uncommon. COVID-19 vaccine side effects on the heart, including myocarditis (inflammation of the heart muscle), are rare and occur most often in young men. Most recover fully with simple treatment.
“It’s important to compare the risks,” said Dr. Curtis. “COVID-19 infection itself carries a much higher chance of heart complications, including myocarditis, blood clots and long-term heart damage. For most people, the benefits of vaccination far outweigh the risks.”
Long-Term Side Effects of the COVID-19 Vaccine
Research and ongoing safety monitoring have shown that COVID-19 vaccines don’t cause long-term side effects. The protection they provide naturally fades over time, but the vaccines themselves don’t stay in your body.
Why You Should Get Vaccinated: The Bottom Line
COVID-19 can lead to serious long-term health problems, and in some cases, even death. Potential health problems include:
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- Long COVID-19 (lasting fatigue, brain fog and breathing issues)
- Heart, lung or kidney damage
- Higher risk of blood clots and stroke
“Most vaccine side effects are mild and go away quickly, while COVID-19 itself can cause serious, long-lasting problems,” said Dr. Curtis. “Getting vaccinated is still the safest way to protect yourself and your family from COVID-19.”
Last Updated: October 16, 2025