Haemophilus influenzae type b (also called Hib disease) causes bacterial meningitis in children less than 5 years of age. In the mid 1980s, according to the Centers for Disease Control (CDC), 1 out of every 200 children became ill from the virus. Among those that got sick, 5 percent ultimately died. Vaccines that protect against Haemophilus influenza type b are widely available in the United States. However, side effects from the vaccine are possible.
Side Effects at the Site of Injection
Comvax, made by the pharmaceutical company Merck, is a combination vaccine that confers protection from Hib disease. Data from a clinical trial conducted by the company revealed that the most common adverse reaction to Comvax was mild symptoms of inflammation at the site of injection. Specifically, some vaccinated children experienced pain, swelling, and redness at the site the shot was given. This reaction was less likely to happen after the second and third injections, compared with the first injection. For example, 34.5 percent experienced pain and soreness after the first injection, whereas 24.3 percent and 23.9 percent experienced pain and soreness after the second and third injections, respectively.
Systemic Side Effects
More rarely, side effects affected the body as a whole; these symptoms are referred to as systemic side effects. Some children experienced the following side effects (reported by their parents), where the number following the symptom is the percentage of infants who experienced that symptom following vaccination: extreme irratibility (57 percent), sleepiness (49.5 percent), unusual high-pitched crying (10.6 percent), lack of appetite (3.9 percent), vomiting (2.1 percent), moderate fever (less than 103 degrees;14.2 percent) and diarrehea (1.7 percent). Less than 1 percent of children experienced other side effects, including upper respitory infection, high fever (greater than 103 degrees), cough and rash.
Anaphylaxis
As with all vaccines, one severe possible side effect is a severe systemic allergy, also called anaphylaxis. An allergic reaction to components in the vaccine occurs very rarely. The CDC advises, "A vaccine, like any medicine, is capable of causing serious problems, such as severe allergic reactions. The risk of Hib vaccine causing serious harm or death is extremely small." Symptoms of an allergic reaction, the CDC warns, are wheezing, difficulty breathing, increased heart rate, or dizziness. Allergic symptoms usually occur a few minutes to a few hours after vaccination, and the CDC advises that the patient receive immediate medical attention.
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