It's National Immunization Month. 5 vaccine truths experts want you to know.

Here's a fact: Vaccines save lives. According to the World Health Organization, 154 million deaths have been prevented globally over the past 50 years thanks to vaccines. That’s the equivalent of saving six lives, most of them infants, every minute of every year. In the United States, a new Centers for Disease Control analysis found that a three-decade-long effort to mobilize families to get vaccines will prevent 1.13 million deaths, 32 million hospitalizations and 508 million illnesses.

“Vaccines have been one of our best preventive health measures that we have,” Dr. Pedro Piedra, professor of molecular virology at Baylor College of Medicine, tells Yahoo Life. “They have done so well that many of the diseases that we worried about decades ago are no longer circulating or circulating at very low levels.”

He adds: “So what vaccines have been able to do is really allow us to live longer. People may not realize that. That has been one of the major benefits beside keeping us healthier.”

Yet vaccine misinformation has grown enough to be deemed a public health threat because it keeps people from getting the shots they need to prevent diseases from spreading. Here are five important things to know about vaccines.

Vaccines protect against severe illness and death

Vaccines help your immune system fight off infections more effectively. Some vaccines prevent diseases from ever occurring — think measles, polio and whooping cough — while others make the illness less severe. It mainly comes down to whether a virus is stable, i.e. predictable, or mutates a lot.

That’s why for certain diseases, people who are vaccinated can still get infected. Some vaccines, such as those for HPV (human papillomavirus), for example, which protect against certain cancers, are close to 100% effective. HPV is a relatively stable virus, unlike SARS‑CoV‑2, which is the virus that causes COVID. SARS‑CoV‑2 mutates rapidly, even more so than the flu, which changes every year — making it harder to have effectiveness rates that high. That’s also why influenza and now COVID vaccines need to be updated each year.

But they’re still considered highly effective vaccines. According to the CDC, people who got the updated COVID-19 vaccine were 54% less likely to get COVID-19 during the four-month period from mid-September 2023 to January 2024. Flu vaccines are similarly effective: They reduce the risk of having to go to the doctor with flu by 40% to 60%. While those numbers might be lower than you might expect, immunologist Andrea Love explained in an Instagram post that “even a vaccine that is 50% effective at preventing symptomatic illness is more protection than if you had no protection.”

Dr. Dean Winslow, professor of infectious diseases at Stanford University School of Medicine, who is encouraging people to get the updated COVID and flu vaccines this fall, agrees. When it comes to COVID and flu vaccines, they’re doing exactly what they’re supposed to do: “They are effective in preventing serious infection, hospitalization and death,” Winslow says.

You can safely get more than one vaccine at a time

Getting multiple vaccines at once — whether it’s childhood immunizations or an adult getting their COVID and influenza shots at the same time — is safe, according to the CDC. “There is no real scientific evidence that getting several vaccines at the same time is harmful,” says Winslow, except for possibly a sore arm and a low-grade fever. “If you’re going to have a little bit of symptoms, you might as well get it over with at once,” he adds.

Greg Marks, pharmacy program coordinator for antimicrobial stewardship at Cedars-Sinai, explains that the immunization schedules for children and adolescents are recommendations developed by experts “who have researched and looked at the data out there and who know these vaccines more than anybody else. There are studies on different combinations of vaccines and no evidence that giving vaccines together as the schedule recommends is associated with any real additional harm — that ‘overloading’ of the immune system.”

He adds that separating out vaccines can mean having to make more appointments to get them, along with more time that you’ll need to take off from work. “And more time you’re potentially exposed too,” he tells Yahoo Life.

Piedra agrees: “You want to protect them as early as you can. If you start making up your own regimen the only person that it’s helping is the parent — it’s not helping the child.”

Vaccines do not cause autism

An overwhelming amount of research shows there is no link between vaccines and autism spectrum disorder. The controversy started with a debunked 1998 paper in the Lancet, which only had 12 study participants and suggested a link between autism and the MMR (measles, mumps and rubella) vaccine. The paper, which was retracted in 2010, was written by Andrew Wakefield, who lost his license for making up data, notes Winslow. But the harm was done, leaving some parents reluctant to immunize their children.

According to the National Academies of Sciences, Engineering and Medicine: “Over the past two decades, many scientists have done rigorous studies to find out if any aspect of vaccines could cause autism,” looking at both vaccine ingredients and getting multiple vaccines in a short time frame and concluded that “none of these studies show any links between vaccines and autism.”

Ingredients in vaccines are safe

The Food and Drug Administration is responsible for making sure vaccines are both safe and effective. “Vaccines are one of the safest products that we have,” says Winslow. “They have to be safe because they're given to millions upon millions of individuals and many are given to very young children. So the FDA is very rigorous in their approach for licensure to ensure the vaccines are safe for the intended population.”

One concern that some people have about vaccines is mercury, which has been one of the most widely used vaccine preservatives. In 2001, however, it was removed from or reduced in all vaccines routinely recommended for children age 6 and under. “The tiny amount of mercury as a preservative in some vaccines has been removed from just about all vaccines, but even the amount is less than you’d be exposed to if you ate seafood every day,” says Winslow. To put it in perspective, the small amount of mercury still in a minority of vaccines is roughly the same amount you’d find in a 3-ounce can of tuna fish, according to the FDA.

Piedra explains that there are also different types of mercury. The one found in some vaccines is thimerosal, which he says is “a safer mercury than that which is found, say, in things we eat. It’s different in how it is metabolized.” More specifically, thimerosal is easily cleared from the body so it doesn’t build up to harmful levels, according to the CDC.

It's important to note that some vaccines contain ingredients that people may be allergic to. For example, influenza and yellow fever vaccines are both made in eggs, which means these vaccines contain egg proteins. Although the CDC recommends talking with your doctor before getting the flu shot, the organization states that severe allergic reactions in people with egg allergies are considered rare and still recommends getting the shots as needed.

Getting vaccinated protects your health — and others

Vaccines not only protect you from getting sick, but they also safeguard others in your household and community. Peidra explains that, with infectious diseases, if the majority of people are vaccinated, it prevents large outbreaks from occurring. It also protects those who can’t be vaccinated against certain diseases. This is the concept behind herd immunity, says Marks.

“This is an important concept because there are people who are immunocompromised who can be vaccinated but their response might be reduced, so having that herd immunity is very important for people with these conditions,” he says. Marks says that newborns, for example, can’t be vaccinated until a certain age, along with people who have allergies to certain components in vaccines.

However, Winslow says that with COVID, we may never reach herd immunity because of how rapidly the virus mutates. But regarding the COVID vaccine, “Even if it doesn't 100% reduce your own risk of infection, you’re still doing this not only for yourself but for other people. For me, it’s being a good citizen.”