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Health: Vaccines rigorously tested for side effects before coming to market

Resources and information

These websites have been recommended by the experts as the best places on the internet to find reliable information about vaccines.

“I also tell people that the absolute best source of information is always going to be your medical provider because that medical provider knows your family, knows your child and really can help you make the best decisions for your individual child,” said Colorado State Epidemiologist Dr. Rachel Herlihy.

The Centers for Disease Control and Prevention: From this site, you can access vaccine information statements, which is the information health-care providers are required to give or to offer a patient when they administer vaccinations. You’ll also find a comprehensive list of all potential side effects for any given vaccine, ranked from mild to severe, and how common they are.

Children’s Hospital of Philadelphia Vaccine Education Center: Herlihy said children’s hospitals are a pretty well-trusted entity, and this one is her favorite. The site is very comprehensive, covering everything from detailed information on vaccine ingredients to dosing safety to tips for evaluating media reports and scientific information and studies about vaccines.

Immunize for Good: This Colorado-based website is targeted at parents, explains things in easy-to-understand language and includes links to more information. “It’s a great spot for parents to just get some facts,” said Eagle County Disease Prevention Manager Rebecca Larson.

The Institute for Vaccine Safety: The Johns Hopkins Bloomberg School of Public Health runs this site. Here, you’ll find an independent assessment of vaccines and vaccine safety. It’s a little more technical than other sites listed here, but provides a substantial amount of science-based information.

Vaccine Safety Net: The Vaccine Safety Net is a global network of websites, evaluated by the World Health Organization, that provides reliable information on vaccine safety. Here, you’ll find links to websites hosted by organizations from around the world, including some of those listed above.

Editor's note: This is the first part of a two-part series of articles about vaccines.

Medications are tested, approved and prescribed because a community of scientists and physicians has concluded that the benefits outweigh the risk of side effects. When it comes to vaccines, this is especially true and, in fact, vaccines go through one of the most rigorous testing processes of any medication, said Colorado State Epidemiologist Dr. Rachel Herlihy.

"A vaccine might take 20 years to come to market … and it's important to keep in mind that vaccine trials are much more rigorous than lots of drug trials because vaccines are held to a higher standard when it comes to side effects," Herlihy said, who is also a physician trained in preventive medicine and oversees the Colorado Department of Public Health and Environment's communicable disease and immunization branches.

"They really should be (held to a higher standard) because they are given as a preventive measure to help healthy individuals, in contrast to something like a chemotherapeutic agent, which is given to someone who is very sick, has cancer, and we might be much more willing to accept side effects for a cancer treatment drug than we would be for something like a vaccine."

In fact, Herlihy said, the standards for vaccines in the United States are higher than in other countries.

"There are some vaccines that are licensed overseas that are not licensed in the United States because we don't have the tolerance for some side effects that other countries might have," she said.

After the U.S. Food and Drug Administration licenses a new vaccine, it is reviewed by the Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices, which is composed of medical and public health experts who decide whether to recommend a vaccine for routine administration in the United States.

According to the CDC, as a part of all the testing and vetting any given vaccine must go through before it arrives in your doctor's office, new vaccines must also be tested alongside others that are already recommended for a particular-age child to ensure the combination is safe.

"Every new vaccine that comes on the market must be studied along with the other vaccines that are given at that age to make sure that there's no interference or complications that occur from adding a new vaccine to the existing immunization schedule," Herlihy said.

While the CDC does state that certain combinations of vaccines that are given together can cause fever and occasionally febrile seizures, which is a convulsion that can happen in a child as a result of a spike in body temperature, the CDC states that these are temporary and do not cause any lasting damage. Therefore, both the Advisory Committee on Immunization Practices and the American Academy of Pediatrics recommend getting all routine childhood vaccines on time.

Delaying a vaccination or altering the recommended vaccination schedule, Herlihy said, can lead to an increased risk of side effects.

"If you delay the MMR vaccine, you actually see an increase in adverse events," Herlihy said. "You see an increase in febrile seizures … so it's important to actually give vaccines on time, and in some cases, you actually see fewer side effects from those vaccines if you give them on time versus delay them."

Common versus rare

While they are carefully and thoroughly tested, vaccines, like any medication, do come with potential side effects. The most common of these, Herlihy said, are soreness at the injection site, fever and headache, all of which she said are a sign the vaccine is doing its job.

"Those are all really indicators that your immune system is responding to the vaccine, which is what we want to have happen," she said. "A fever especially is an indicator that your body is actually doing its job and creating antibodies and mounting a response to the antigen that it's received through that vaccine."

An antigen is the substance in a vaccine that provokes the immune system to generate antibodies against it. An antibody is a protein generated by the immune system in response to the presence of a specific antigen. Antibodies attach to that antigen to help counter its effects. All of this stimulates and strengthens the immune system.

The World Health Organization sets standards for pharmaceutical industry rankings of potential vaccine side effects, including common, uncommon, rare and very rare, said Herlihy.

"So, something that is common would occur in one in 100 to one in 10, so less than one in 100," she said. "And then you get something like a very rare side effect or adverse effect that would occur in less than one individual in 10,000."

The CDC lists every available vaccine and all its potential side effects, including the likelihood of the side effect, on the vaccines and immunizations section of its website. Take, for example, the measles, mumps and rubella (commonly known as MMR) vaccine. According to the CDC's website, mild problems include fever in up to 1 person out of 6, mild rash in about 1 person out of 20 and swelling of glands in the cheeks or neck in about 1 person out of 75.

If these problems occur, states the CDC, then it is usually within six days to 14 days after the shot. They occur less often after the second dose.

An example of a moderate problem, according to the website, is a seizure (jerking or starting) caused by a fever, which occurs in about one dose out of 3,000 doses. Severe, or very rare, problems include a serious reaction in less than 1 dose out of 1 million doses. Several other severe problems have been reported — including deafness, long-term seizures and permanent brain damage — after a child gets the MMR vaccine; these, states the CDC, are so rare that it is hard to tell whether they are caused by the vaccine.

A vaccine myth

When determining the safety of a vaccine, the FDA must determine whether the vaccine's benefits clearly and definitively outweigh its risks. The Children's Hospital of Philadelphia's Vaccine Education Center — one of Herlihy's favorite resources for vaccine information — puts it like this:

"The first definition of the word 'safe' is 'harmless.' This definition would imply that any negative consequence of a vaccine would make the vaccine unsafe. Using this definition, no vaccine is 100 percent safe. … The second definition of the word 'safe' is 'having been preserved from a real danger.' Using this definition, the danger (the disease) must be significantly greater than the means of protecting against the danger (the vaccine)."

Despite these definitions, though, Herlihy said a common myth when it comes to side effects associated with vaccines is that the side effects from the vaccination are more common than the risks of the disease they're preventing. In fact, she said, the opposite is true.

"I think the encephalitis example is a good one with the MMR vaccine," Herlihy said. "Encephalitis is brain inflammation or swelling. So, if you look at the disease measles, encephalitis occurs in about one child 1 of 1,000. But if you look at encephalitis as a potential side effect of that vaccine, it's less than 1 in 1 million."

Education is key

Rebecca Larson, manager for the Disease Prevention and Control Department at Eagle County Public Health and Environment, agrees that this is a common myth and stresses the importance of educating oneself not only about the potential side effects of a vaccine, but also about the potential risks associated with the disease it's preventing.

"Any provider who provides vaccinations is required to provide the vaccine information statement for every vaccine administered," Larson said. "And on those statements, not only does it talk about the benefits of the vaccine, but also the disease itself that it's protecting against, the facts and symptoms of the disease and the risks of getting that disease.

"Sometimes I feel like maybe we gloss over that, but the reality is some of these diseases are very serious. … While sometimes you think maybe the symptoms will be mild, they can be severe and we don't know who's going to get the mild case of the disease and who's going to get the severe case and that's a risk you take if you choose not to get vaccinated."

At the end of the day, she said, health care providers understand that parents are trying to do what's best for their child.

"I think that the challenging thing regarding immunizations, especially when parents are trying to make this decision, is most parents are wanting to do what they think is best for their child's health" said Larson. "And I don't think a health care provider would question that but I think it's really important to seek out those facts, talk with your physician about the concerns, to really make an informed decision based on the facts and also know the risks of the diseases."

Perhaps also important to keep in mind is that, often, doctors are parents, too.

"One myth is that vaccines cause autism," said Dr. Dennis Lipton, who practices internal medicine at Vail Valley Medical Center. "Since I have children of my own, I was very concerned about this one. Careful review of the literature proves it to be a myth. I am not an expert in autism, but I know autism rates have increased markedly in the past 50 years. We don't know the exact cause.

"My overall feeling is that the benefits of vaccines far outweigh any real or perceived downside. After research and consideration, my family and I choose to get all recommended vaccines."