There are four reasons that babies—and even teens or adults—who receive a vaccine for the first time may need more than one dose:. Some people believe that naturally acquired immunity—immunity from having the disease itself—is better than the immunity provided by vaccines.
However, natural infections can cause severe complications and be deadly. This is true even for diseases that many people consider mild, like chickenpox. It is impossible to predict who will get serious infections that may lead to hospitalization. Vaccines, like any medication, can cause side effects. The most common side effects are mild. However, many vaccine-preventable disease symptoms can be serious, or even deadly. Although many of these diseases are rare in this country, they do circulate around the world and can be brought into the U.
Even with advances in health care, the diseases that vaccines prevent can still be very serious — and vaccination is the best way to prevent them. Skip directly to site content Skip directly to page options Skip directly to A-Z link. Provider Resources for Vaccine Conversations with Parents. Section Navigation. Facebook Twitter LinkedIn Syndicate. Understanding How Vaccines Work. Minus Related Pages. On This Page. Macrophages media icon are white blood cells that swallow up and digest germs, plus dead or dying cells.
The macrophages leave behind parts of the invading germs called antigens. The body identifies antigens as dangerous and stimulates antibodies to attack them. B-lymphocytes are defensive white blood cells. They produce antibodies that attack the antigens left behind by the macrophages. T-lymphocytes are another type of defensive white blood cell. They attack cells in the body that have already been infected.
In this vaccine, the isolated measles virus went through the attenuation process 80 times. This vaccine was quite effective, but some recipients still experienced mild measles symptoms, such as fever and rash. These mild side effects were unacceptable to the vaccine developers.
Thus, the vaccine went through the attenuation process another 40 times. A new and improved vaccine came out in Thanks to this new vaccine, side effects were rare. Not only that, but measles cases plummeted in the United States.
In , there were nearly thousand measles cases; by , there were under 50 thousand cases. Learn more about the history of the measles vaccine here. In other words, live virus vaccines and other types of vaccines are regularly tested, monitored, and improved.
According to the CDC , adenovirus causes a range of illnesses, like bronchitis, pneumonia and conjunctivitis pink eye. They can also cause cold-like symptoms, like a fever and sore throat. People with weakened immune systems or existing respiratory or cardiac diseases are more likely to get very sick from an adenovirus infection.
Similar to a flu vaccine, the most common side effects for current COVID vaccines include pain at the injection site, and about one in five people may experience minor side effects like low-grade fever or nausea. Live virus vaccines are also being increasingly used by researchers as "viral vectors" for gene therapy. Because the weakened viruses are still "programmed" to attack specific cells, they can latch onto and implant a cell with modified DNA to potentially treat inheritable genetic disorders.
Additional research on using vaccines in this way is needed. One downside of live vaccines is that they require refrigeration, which can limit the ability to use them in resource-limited areas. If these vaccines are not kept at the correct temperature, they can become inactive. If this happens, immunization may not be effective.
Also, some live virus vaccines come as a powder and require reconstitution restoring from a dry state with a specific diluent fluid before they can be administered. Administrator error can also undermine the effectiveness of the vaccine. Although small, there is the risk that the weakened live virus could end up causing the illness it was meant to prevent. This is especially the case in people who are severely immunocompromised. In the absence of a normal immune response, the weakened virus has the potential to replicate and, in rare cases, reverse to its natural virulent state.
As a general rule, live attenuated vaccines should not be given to severely immunocompromised people, including:. Even so, there are times when the benefits of vaccination in these individuals outweigh the risks. In such cases, expert consultation is needed to determine whether the use of a live attenuated vaccine is appropriate. Vaccines are one of the true public health success stories.
Tetanus, diphtheria, mumps, and polio are examples of diseases that were once common but are now rarely seen in the United States. Even if eradication is not achieved, vaccines can significantly reduce the incidence and severity of many dread infections.
With that said, the recent anti-vaccination movement threatens to reverse many of those gains with diseases like measles. This highly contagious viral disease was declared eliminated in the United States in , but now is reemerging in regional outbreaks not only in America but abroad. Get our printable guide for your next doctor's appointment to help you ask the right questions. Sign up for our Health Tip of the Day newsletter, and receive daily tips that will help you live your healthiest life.
Centers for Disease Control and Prevention. About the vaccine. Minor PD. Live attenuated vaccines: Historical successes and current challenges. World Health Organization.
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