The body’s immune system helps protect against pathogens that cause infection. Most of the time, it’s an efficient system. It either keeps microorganisms out or tracks them down and gets rid of them. However, some pathogens can overwhelm the immune system. When this happens, it can cause serious illness. The pathogens most likely to cause problems are the ones the body doesn’t recognize. Vaccination is a way to “teach” the immune system how to recognize and eliminate an organism. That way, your body is prepared if you’re ever exposed. Vaccinations are an important form of primary prevention. That means they can protect people from getting sick. Vaccinations have allowed us to control diseases that once threatened many lives, such as measles, polio, tetanus and whooping cough. It’s important that as many people as possible get vaccinated. Vaccinations don’t just protect individuals. When enough people are vaccinated, it helps protect society. This occurs through herd immunity. Widespread vaccinations make it less likely that a susceptible person will come into contact with someone who has a particular disease.
A healthy immune system defends against invaders. The immune system is composed of several types of cells. These cells defend against and remove harmful pathogens. However, they have to recognize that an invader is dangerous. Vaccination teaches the body to recognize new diseases. It stimulates the body to make antibodies against antigens of pathogens. It also primes immune cells to remember the types of antigens that cause infection. That allows for a faster response to the disease in the future. Vaccines work by exposing you to a safe version of a disease. This can take the form of a protein or sugar from the makeup of a pathogen, dead or inactivated form of a pathogen, toxoid containing toxin made by a pathogen or a weakened pathogen. When the body responds to the vaccine, it builds an adaptive immune response. This helps equip the body to fight off an actual infection. Vaccines are usually given by injection. Most vaccines contain two parts. The first is the antigen. This is the piece of the disease your body must learn to recognize. The second is the adjuvant. The adjuvant sends a danger signal to your body. It helps your immune system to respond more strongly against the antigen as an infection. This helps you develop immunity.
Allergy, exaggerated and sometimes harmful reactions to external substances, called allergens. Allergy may result from exposure to such common allergens as plant pollens from grasses, trees, or ragweed; animal danders, which are tiny scales shed from the skin and hair of cats and other furred animals; arachnids and insects, such as house dust mites, bees, and wasps; and drugs, such as penicillin. The most common food allergies are caused by crustacean shellfish, eggs, fish, milk, peanuts, soybeans, tree nuts, and wheat. Researchers estimate that at least 24 million people in the United States suffer from allergies—about 19 percent of the population. In an allergic reaction, the immune system mistakenly interprets a harmless substance as a harmful one. The immune system responds by producing antibodies called immunoglobulin E (IgE). These IgE antibodies are designed to help neutralize specific parasitic invaders and protect the person from future exposures. Upon first exposure to an allergen, no allergic symptoms develop. But when the person is exposed to the same substance at a later time, the IgE antibodies against the allergen activate an allergic reaction. Allergy symptoms may include itching, sneezing, a stuffy nose, watery eyes, inflammation of the airways in the lungs and wheezing (known as asthma), and even allergic shock and death in rare situations.
After allergy antibodies have been formed in a person’s body in response to a particular allergen, an allergic reaction can occur when the person comes in contact with that allergen. Depending on the substance, allergens can be inhaled, eaten, injected, or contacted by the skin. When allergy antibodies are activated by an allergen, they cause body cells to release a substance called histamine, a chemical that dilates blood vessels, promotes fluid secretions, and stimulates nerves that cause muscles to spasm. These reactions create various allergy symptoms. In a person with hay fever, for example, pollen allergens cause a number of symptoms. When pollen is breathed in through the nose, the release of histamine in the nasal passages causes violent, repetitive sneezing, release of watery fluids, and itching. Sometimes pollen triggers tissue swelling, which can cause blocked nasal passages, with consequent loss of smell and taste. When pollen allergens affect the eyes, they become itchy, red, and watery. Allergens that affect the lungs cause secretion of mucus and inflammation, swelling, and narrowing of the airways, resulting in asthma. Symptoms include spasms of the airways and sudden difficulty in breathing. Allergic reactions can also be triggered throughout the entire body, rather than in one specific location. Called allergic or anaphylactic shock, this response occurs when many cells throughout the body react simultaneously to an allergen, such as bee sting venom. The person may experience hives or welts on the skin, itching all over the body, asthmatic spasms in the lungs, or a sudden drop in blood pressure. An additional danger is the possibility of swelling in the throat, tongue, and larynx (voice box), which can close the upper airways and cause fatal choking.
Researchers have identified a definite genetic predisposition to allergies. For example, if one parent has allergies, there is an increased risk that some of the children will also have allergies, although the children may not be sensitive to the same allergens as the parent. If both parents have allergies, the risk that the children will develop allergies is even greater. The most typical time for allergies to develop is in young adulthood, although allergies can develop in a person of almost any age, even within a few months after birth. Allergies in infants are most commonly associated with foods and viral respiratory infections. For reasons that are not clearly understood, children with allergies tend to outgrow them. The child’s body somehow readjusts its response to allergens, even those that cause severe reactions, such as food, drugs (especially penicillin), and stinging insects. Patients are sometimes surprised by the abrupt onset of allergies in adult life. This can occur when the combination of a person’s genetic makeup and a longstanding but unnoticed reactivity to an allergen finally culminates in a detectable disease. This so-called allergic threshold is crossed when allergens finally produce enough reaction in the body to cause detectable symptoms. Several as yet unknown genes may be involved in this process.
Many people think that emotions, such as stress, cause allergies, but most physicians believe this is incorrect. In fact, the opposite may be true: People with allergies live with symptoms that can produce serious emotional upset. For example, a person with asthma may have fears about losing the ability to breathe, or possibly choking to death. Allergies, including asthma, are caused by biological factors, although emotions may aggravate an allergic reaction. Researchers aren’t exactly sure why the immune system causes an allergic reaction when a normally harmless foreign substance enters the body. Allergies have a genetic component. This means parents can pass them down to their children. However, only a general susceptibility to allergic reaction is genetic. Specific allergies aren’t passed down. For instance, if your mother is allergic to shellfish, it doesn’t necessarily mean that you’ll be, too.
Vaccines are intended to produce active immunity to specific antigens. An adverse reaction is an undesirable side effect that occurs after a vaccination. Vaccine adverse reactions are classified as 1) local, 2) systemic, or 3) allergic (additional information external icon). Local reactions (e.g., redness) are usually the least severe and most frequent. Systemic reactions (e.g., fever) occur less frequently than local reactions, and severe allergic reactions (e.g., anaphylaxis) are the least frequent reactions. Severe adverse reactions are rare. Some of the systemic reactions may be complicated by the onset of syncope. Syncope (vasovagal or vasodepressor reaction) can occur after vaccination and is most common among adolescents and young adults. In 2005, the Vaccine Adverse Event Reporting System (VAERS) began detecting a trend of increasing syncope reports that coincided with the licensure of 3 vaccines for adolescents: human papillomavirus (HPV), MenACWY, and Tdap. Concern among adolescents has been the risk for serious secondary injuries, including skull fracture and cerebral hemorrhage. Of 463 VAERS reports of syncope during January 1, 2005, to July 31, 2007, a total of 41 listed syncope with secondary injury with information on the timing after vaccination, and the majority of these syncope reports (76%) occurred among adolescents. Among all age groups, 80% of reported syncope episodes occur within 15 minutes of vaccine administration (additional information). Providers should take appropriate measures to prevent injuries if a patient becomes weak or dizzy or loses consciousness. Adolescents and adults should be seated or lying down during vaccination. Vaccine providers, particularly when vaccinating adolescents, should consider observing patients (with patients seated or lying down) for 15 minutes after vaccination to decrease the risk for injury should they faint. If syncope develops, patients should be observed until the symptoms resolve. Although allergic reactions are a common concern for vaccine providers, these reactions are uncommon and anaphylaxis following vaccines is rare, occurring at a rate of approximately one per million doses for many vaccines. Epinephrine and equipment for managing an airway should be available for immediate use. The best practice to prevent allergic reactions is to identify individuals at increased risk by obtaining a history of allergy to previous vaccinations and vaccine components that might indicate an underlying hypersensitivity. Acute allergic reactions following vaccinations might be caused by the vaccine antigen, residual animal protein, antimicrobial agents, preservatives, stabilizers, or other vaccine components.
Vaccine providers should be familiar with identifying immediate-type allergic reactions, including anaphylaxis, and be competent in treating these events at the time of vaccine administration. Providers should also have a plan in place to contact emergency medical services immediately in the event of a severe acute vaccine reaction. Allergic reactions can include: local or generalized urticaria (hives) or angioedema; respiratory compromise due to wheezing or swelling of the throat; hypotension; and shock. Immediate-immunoglobulin E (IgE)–mediated (type 1) immune reactions, such as anaphylaxis, usually occur within minutes of parenteral administration and involve specific IgE interactions with discrete antigens. Rapid recognition and initiation of treatment are required to prevent possible progression to respiratory failure or cardiovascular collapse. It is important to note that urticaria may not be present in all cases of anaphylaxis. For respiratory or cardiovascular symptoms, or other signs or symptoms of anaphylaxis, immediate intramuscular epinephrine is the treatment of choice. Additional doses of epinephrine as well as other drugs also might be indicated. If hypotension is present, the patient should be placed in a recumbent position with the legs elevated. Maintenance of the airway, oxygen administration, and intravenous normal saline might be necessary. After the patient is stabilized, arrangements should be made for immediate transfer to an emergency facility for additional evaluation and treatment. Because anaphylaxis may recur after patients begin to recover, monitoring in a medical facility for several hours is advised, even after complete resolution of symptoms and signs.
For an individual patient who has experienced an immediate reaction to immunization, it is important to identify the type of reaction that occurred, obtain a history of prior allergic reactions, and try to identify the particular agent responsible. In general, a history of a severe allergic reaction to a vaccine should be considered a contraindication to additional doses of the same vaccine. Referral of the individual to an allergist for evaluation is usually indicated to possibly determine the component responsible, before making decisions regarding administration of the additional doses of the same vaccine or other vaccines that have the same components. Patients who have not had a severe allergic reaction following a vaccine, but who have a history of possible allergy to a vaccine component can often be vaccinated safely after careful evaluation