Vaccines have prevented an estimated 154 million deaths worldwide since 1974.
In the United States, for children born between 1994 and 2023, vaccines prevented 508 million cases of illness, 32 million hospitalizations and 1.13 million deaths.
But childhood vaccination rates in the U.S. are dropping and rates of vaccine hesitancy—being unsure or conflicted about receiving available vaccines—are on the rise. Misinformation about vaccines spreads quickly on social media, and vaccines became a political issue during the COVID-19 pandemic, which made neutral and objective conversation about vaccines’ benefits and risks difficult.
We spoke to UNC Health infectious diseases expert David J. Weber, MD, MPH, about concerns some people have about vaccines.
Concern: I’m not sure vaccines have been studied well enough.
Some people balked at the speed at which the COVID-19 vaccines were developed. But that fast development was only possible because work had already been underway on that type of vaccine (mRNA vaccines). Its quick timeline was due to increased funding, given the impact of the pandemic. Safety steps were not skipped, Dr. Weber says.
“All vaccines have to show efficacy and safety in two large randomized, controlled trials before they’re accepted by the Food and Drug Administration,” Dr. Weber says. “These are carefully vetted, multi-stage trials that have to meet qualifications set by the FDA.”
Most vaccines have gone through many more than two trials, both in this country and worldwide.
“Then there are careful looks at safety with separate panels at the FDA and the Centers for Disease Control and Prevention,” Dr. Weber says. “Each panel is an outside group of experts, none of whom can have a conflict of interest, such as an investment in a pharmaceutical company. It’s a rigorous process with lots of steps.”
In addition to the panels of outside experts, staff committees and the directors of the FDA and CDC must approve the vaccine and recommendations for use.
For each vaccine application, reviewers are looking to see if the benefits of the vaccine in preventing serious disease are significantly greater than any potential side effects and how the vaccine compares to no treatment at all.
Studies and reviews of vaccines continue after approval.
“There is continued review of vaccine safety and efficacy,” Dr. Weber says. “Scientists are studying impacts worldwide, and there are reporting systems for vaccine safety concerns. If problems are found, vaccines would be withdrawn from the market or have additional restrictions.”
Concern: I’m healthy, so I don’t need a vaccine.
Concern: I think the disease is not that bad, and I’ll have natural immunity if I get it.
Both of these concerns relate to a personal risk-benefit analysis; you may be concerned that perceived risks of a vaccine outnumber the perceived benefits of preventing a certain disease. Unfortunately, we don’t always have an accurate view of risks or benefits when it comes to preventable disease or accidents.
“People overestimate rare occurrences and underestimate common occurrences,” Dr. Weber says.
For example: The odds of dying in a car crash are around 1 in 95, while the odds of dying in an airplane crash are too small to calculate, according to the National Safety Council. And yet, fear of flying is much more common than fear of riding in a car.
We wear seatbelts and follow rules of the road to make driving safer, and we get vaccines to make living in a world full of germs and diseases safer, Dr. Weber says.
“Do we want to go back to a world in which 20,000 children a year are paralyzed by polio or where 20,000 children had birth defects from rubella?” Dr. Weber says. “Do we want hundreds of children dying of measles and its impairments? People don’t remember, but that’s the world we had in the 1950s.”
As for COVID-19: While many people have mild symptoms, an estimated 17 million adults currently have long COVID, affecting their ability to work or live the life they want to live.
While you may think that only older people need a flu shot—70 percent of flu-related deaths in 2022-2023 were in people older than 65—there were still 1,538 people younger than 50 who lost their lives the same flu season.
“For vaccines approved in the U.S., the data is overwhelming that the benefits exceed the risks. If the vaccine can prevent the disease, why take the risk of having the disease, for you or your child? The risks of the natural disease are higher than the risk associated with any vaccine side effects,” Dr. Weber says.
Concern: I’m worried vaccines cause autism, infertility or some other condition.
Vaccines do have potential for serious side effects and complications; for example, though rare, a COVID-19 vaccination can cause myocarditis, or inflammation of the heart, which is treatable, and the flu vaccine has been associated with occasional cases of Guillain-Barré syndrome. (Still, the risk of myocarditis is higher after COVID-19 then after a COVID-19 vaccine, and the risk of Guillain-Barré is higher after the flu than after the vaccine, Dr. Weber notes.)
However, Dr. Weber says there is no evidence that vaccines cause autism.
Here’s how that myth started: In 1998, a paper suggesting that the measles, mumps and rubella (MMR) vaccine may lead to autism was published. One of the authors, Andrew Wakefield, deliberately falsified data for this paper, and no study since has been able to show that the MMR vaccine causes autism.
“Association doesn’t mean causation,” Dr. Weber says. “It may be true that everyone with autism had a certain vaccine, but everyone with autism may have also consumed milk. That’s an association. There are other exposures and genetic factors to consider. There have been many studies with no evidence that vaccines cause autism.”
During and after the COVID-19 pandemic, some claimed that the vaccine could cause infertility, but studies have shown no effect on fertility as a result of the vaccine.
Before receiving any vaccine, it’s important to ask what the side effects might be. The most common side effects of a vaccine are mild and short-term pain or swelling at the injection site, muscle and joint aches or fatigue. More serious side effects, such as an allergic reaction, are extremely rare.
Concern: I’ve heard the ingredients in vaccines aren’t safe.
Part of the approval process for vaccines is ensuring that every ingredient in the vaccine is safe. Still, vaccine skeptics continue to single out a few ingredients for safety concerns, despite a lack of evidence of harm.
Thimerosal is a preservative that prevents bacteria from growing in a vial of a multi-dose vaccine. This preservative has mercury (a type of mercury called ethylmercury) but not the kind of mercury that can be toxic (methylmercury).
“There was no harm shown with that tiny amount of thimerosal, but now it’s been taken out of vaccines and hasn’t been in childhood vaccines for decades,” Dr. Weber says.
Some vaccines may include aluminum salts as an adjuvant, or something that makes the vaccine work better. At extremely high levels—much higher than is in vaccines—there is a potential link to neurological and kidney problems. These adjuvants have been used safely for more than 70 years, and we all have regular exposure to aluminum in the air and some foods and medications.
To Dr. Weber, this is an example of focusing on the highly unlikely plane crash rather than the more likely risk of a car crash; we’re fearful of something that’s safe while tolerating risks that can cause us greater harm.
“People may see the vaccine as harmful, but do you know all the ingredients in a bag of potato chips?” he says. “A processed food item may have a list of 20 different things, plus a lot of sugar and sodium. These things are not healthy, but most people still eat them.”
Concern: I got a vaccine, and I still got sick.
It’s true that you can get a flu shot and still get the flu (or it could be a respiratory virus that seems like the flu). However, if you received a flu shot and get the flu, the shot likely will reduce the risk of serious disease. The same is true for the COVID-19 vaccines; you should have a less serious case if you do get sick.
“You might get sick, but vaccines prevent hospitalization and death if you do get the illness,” Dr. Weber says.
Dr. Weber notes that you probably wouldn’t stop wearing your seatbelt just because you heard of someone who died in a car accident while wearing one. As with seatbelts, vaccines are meant to work more times than they don’t, but they can’t account for every accident or exposure.
Getting sick after a vaccine is frustrating, but it’s not a reason to give up on vaccinations altogether; the continued effectiveness of vaccines depends on high rates of the population getting them.
“If you want there to be community protection or herd immunity for a disease, then as a society, we have to work to protect people,” Dr. Weber says. “Not everyone can get a vaccine, like a child with leukemia or a newborn baby. Those who can and do are taking part in a social good.”
Concern: I don’t know who to trust regarding vaccines.
There is a lot of data available to you about vaccines: you can access thousands of studies in academic journals and read the CDC fact sheets available about every vaccine. But that’s time-consuming, and sometimes, research studies are difficult to understand. Maybe you’re pregnant and concerned about what’s safe, or perhaps you’re immunocompromised and not sure how that changes your risk. Instead of trusting someone on social media to give you the scoop, Dr. Weber recommends talking to your healthcare provider about your specific situation.
“Have a discussion about your concerns,” he says. “I think it’s important to make a decision based on the evidence, and that information is available for vaccines. There’s complete transparency.”
Being able to have these kinds of conversations is one of many reasons why it’s important to find a healthcare provider you trust; when you know your provider has you and your family’s best interests at heart, you’ll be willing to consider the evidence they give you.
“Try to have an open mind when your healthcare provider explains what you’re at risk for and how you can protect yourself,” Dr. Weber says.
If you have questions about vaccines, talk to your doctor. If you need a doctor, find one near you.