Updated: July 19, 2004
The prevalence of childhood asthma has been increasing in the past two decades in many countries, including the United States.1 According to American Lung Association statistics for 2002, over 20 million Americans had asthma, of which 6.1 million were children.2
Asthma is a chronic disease characterized by repeated episodes of wheezing, breathlessness, chest tightness, and coughing. Although there is no known cure for asthma, it can be controlled.
The causes of asthma are not known, but if a person has a parent with asthma, he or she is three to six times more likely to develop asthma than is a person who does not have a parent with asthma.3 Children with asthma may respond differently to infections and environmental exposures such as tobacco smoke and mold than children who don’t have asthma. These facts suggest that asthma could be an immune disorder influenced by genetics.
Some have suggested that the increasing incidence of asthma may be due to vaccinations, primarily to whole cell pertussis vaccine. Some have hypothesized that vaccines might change the balance of immunity towards allergic responses either directly (that is, caused by the immune responses to the vaccine) or indirectly (by altering the balance of immune responses to infections in infancy).
The first study suggesting a possible association between vaccination and asthma was conducted in children born in 1977 in Christchurch, New Zealand.4 In this study there was no evidence of asthma during 5 to 10 years of follow-up among 23 children who received neither pertussis vaccine nor oral polio vaccine, whereas asthma developed in more than 20% of 1,184 children who had been vaccinated. However, the small number of unvaccinated children did not establish a correlation between asthma and vaccines.
A study of 1,934 patients followed from birth to age 12 in a general medical practice in the UK f found that children given an older form of pertussis vaccine (whole-cell vaccine) were 40% more likely to develop asthma than unvaccinated children.5 An indirect mechanism by which vaccines might affect the tendency to develop allergies, perhaps including asthma, would be by preventing infections in childhood, causing an imbalance in immune responses later in life. For example, whooping cough has been suggested to increase the occurrence of allergy and asthma, and it has been theorized that the DTP vaccine could have similar effects.
More recent data, however, do not support the theory that specific vaccines or the number of vaccines administered lead to an increased risk of childhood asthma.
For example, one large study involving 167,240 children from four large health maintenance organizations in Washington, Oregon and California, found no increased risk of developing childhood asthma associated with diphtheria, tetanus, whole cell pertussis, vaccine, measles, mumps, rubella vaccine and oral polio vaccine.6
In another large study, researchers examined whether immunizations received before 18 months of age were related to asthma in later childhood.7 The investigators found that asthma was not associated with the vaccines or the number of vaccinations received.
Vaccines are very important for children with asthma. An analysis by the American Lung Association shows that many hospitalizations due to asthma could be prevented by influenza vaccination, which has been proven to be safe in children and adults with asthma.8
In addition, it is expected that future vaccines against other respiratory infections may reduce the incidence of wheezing and asthma in childhood, since severe infections in young infants caused by some of these agents are associated with wheezing in infancy and asthma later in childhood.