A Thorough Process
The most common components of vaccines are weakened microbes (disease-causing microorganisms), killed microbes, and inactivated toxins. In addition, subunit vaccines, which only use a part of the bacterium or virus, are increasingly being used.Manufacturers conduct stringent tests to make sure that cell lines used for producing viral vaccines do not contain adventitious agents (unwanted viruses) such as simian virus 40 (SV40), which was found in some early polio vaccines. These vaccines had been manufactured in kidney cells from simians (monkeys) that harbored SV40. Following its discovery, SV40 was removed from vaccines, and vaccines have been free of the virus since the early 1960s. CBER scientists are developing potentially better methods to detect such infectious agents.
Developing vaccines is a thorough and rigorous process, Egan says. Vaccines are tested for safety on animals first, and then in humans during several phases of clinical trials. The most important clinical trial for the recently licensed vaccine Prevnar involved nearly 40,000 people, equally divided between those who received the vaccine and those who did not. Prevnar was approved to prevent invasive pneumococcal diseases such as meningitis.
A group of FDA scientists reviews data and the proposed labeling of the vaccine, which includes directions for use and information about potential side effects. The committee also reviews manufacturing protocols, conducts its own tests, and inspects the manufacturing facility. The FDA's Vaccines and Related Biological Products Advisory Committee, which includes scientific experts and consumer representatives, can be consulted at any time to review data and recommend action to the agency.
After a vaccine is licensed, the FDA generally requires that manufacturers use validated methods to test samples from each vaccine lot for safety, potency, and purity prior to its release for public use. The FDA also tests selected lots and products to help assure the accuracy of tests conducted by the manufacturers.
Common Concerns
"Most vaccines cause some side effects, but they are usually minor and short-lived like low-grade fever and soreness at the injection site," Midthun says. Serious vaccine reactions--causing disability, hospitalization, or death--are extremely rare but they can happen.Like any medicine, vaccines carry a small risk of serious harm such as severe allergic reaction. But experts point out that the risk of being harmed by a vaccine is much lower than the risk that comes with infectious diseases. For example, in 1976, the swine influenza (flu) vaccine was associated with a severe paralytic illness called Guillain-Barre Syndrome (GBS). According to the CDC's vaccine information sheet on the influenza vaccine, "if there is a risk of GBS from current influenza vaccines, it is estimated at 1 or 2 cases per million persons vaccinated, much less than the risk of severe influenza, which can be prevented by vaccination." Each year, flu causes tens of thousands of deaths, mostly among older people. Most people who get the influenza vaccine have no serious problem from it.
And though some people worry about it, you can't get the flu from the flu vaccine, Midthun says. "Just as there are no vaccines that are 100 percent safe, there are also none that are 100 percent effective," she says. "So you may get the flu soon after you received the vaccine, before it could be expected to protect you. It does not mean the shot gave you the flu," she says.
Some live virus vaccines, such as the chickenpox vaccine, can cause mild versions of the disease they protect against, says Goodman. "But this is usually only a serious problem if the patient has a severely compromised immune system." And vaccines are generally not advised for such people. It's important to talk with your doctor about the benefits and risks of vaccines, and any concerns you may have, specifically as it relates to you and your family (see "Steps to Take When You Vaccinate"). If you or your child has previously had a significant reaction to a vaccine, that may affect the risk/benefit ratio for the individual and whether that vaccine should be recommended again.
