Undervaccination results in increased risk for whooping cough in young children

Undervaccination – not receiving all recommended vaccinations or not being vaccinated according to the Advisory Committee on Immunization Practices schedule – results in an increased risk for whooping cough in children 3 to 36 months of age, according to a new Kaiser Permanente study. The study was published today in JAMA Pediatrics. In 2012, the United States experienced its largest whooping cough outbreak in 50 years.

Kaiser Permanente researchers used the Vaccine Safety Datalink – a collaborative effort among the Centers for Disease Control and Prevention and eight managed care organizations – in this study to analyze the immunization records of 323,247 children born between 2004 and 2008. Seventy-two patients with laboratory-confirmed cases of pertussis, commonly referred to as whooping cough, from this group were compared to four times as many children of the same age and gender who were not infected with whooping cough.

The diptheria, tetanus toxoids, and acelluar pertussis (DTaP) vaccine protects against whooping cough. It is given in a series to children at two months, four months, six months and 15-18 months of age and as a booster before kindergarten.

Of the 72 whooping cough patients in this study,16 percent were hospitalized and 47 percent were undervaccinated for the DTaP vaccine when the infection was diagnosed compared to 22 percent of patients who were not infected. Undervaccination was defined as missing any of the four scheduled DTaP vaccine doses. Children undervaccinated for three or four doses were more than 18 and 28 times as likely to have been diagnosed with whooping cough than children who were vaccinated according to ACIP immunization guidelines.

"A growing number of parents are choosing to have their children follow alternative vaccination schedules," said lead study author Jason Glanz, Ph.D., a senior scientist at Kaiser Permanente's Institute for Health Research. "Recent whooping cough outbreaks have raised concerns that undervaccination may place children at risk for serious infectious diseases. The findings of this study indicate that those concerns have merit. Children, and the larger community, are more likely to contract these types of diseases if they are not vaccinated according to recommended guidelines."

Pertussis is a highly contagious bacterial disease that causes uncontrollable, violent coughing and can be deadly in infants, especially those under two months of age who are too young to be fully vaccinated. In 1976, there were just over 1,000 reported cases of pertussis in the U.S. By 2012, it climbed to 41,880 cases. The DTaP vaccine has been shown to be 98 percent effective in preventing whooping cough.

Kaiser Permanente is committed to furthering understanding of vaccine effectiveness and safety. Recent Kaiser Permanente studies found that nearly half of children under two years of age receive some vaccinations late, and children of parents who refuse vaccines are nine times more likely to get chickenpox and 23 times more likely to get whooping cough than fully immunized children. According to Glanz, this type of research provides parents and physicians with a larger body of evidence to have informed discussions about alternative vaccination schedules.