According to a new study, the largest whooping cough outbreak since 1947 has been linked to clusters of unvaccinated children.
California’s 2010 outbreak of Whooping Cough, also known as Pertussis, infected 9,120 young children and was connected with 10 infant deaths. Although health officials suspected the outbreak was the result of some children not being vaccinated, the new study confirms these suspicions.
Researchers examined the location of whooping cough cases in 2010 and compared them with the areas where parents applied for an exemption from school policies requiring vaccines due to personal beliefs, rather than for medical reasons. (Some children with compromised immune systems aren’t able to be vaccinated.)
Whooping Cough is highly contagious, spreading quickly through a community. So research experts had to map not only the location of outbreak clusters, but also when they appeared. Published in the journal, Pediatrics, last week, the study found that people living in areas where a large number of parents had opted out of vaccines were 2.5 times as likely to live in an area with a large number of whooping cough cases.
In addition, the outbreak did not come from areas with poorer socioeconomic households, where there may be less access to health care. Instead the clusters of both Whooping Cough infections and those who opted out of vaccinations were in areas with higher socioeconomic characteristics. In these regions people were more likely to be highly educated, have fewer children and make more money annually. Statewide about 2 percent of parents file an exemption, but the number varied greatly from one community to the next. In some schools more than three-quarters of the families filed exemptions.
Jessica Atwell, lead author on the study and a Ph.D. candidate at the Johns Hopkins University School of Public Health, points out that whooping cough and measles are very virulent diseases. While a person with the flu can expect to infect one to two unvaccinated people, a person with Whooping Cough can infect approximately 13 to 15 people if they are not vaccinated. Atwell said in order to keep a disease like Whooping Cough from spreading, a community must have an immunity rate of between 93 and 95 percent. When the number drops below 93 percent, a community loses its “herd immunity” to highly contagious germs.
Whooping Cough is particularly dangerous for young infants. According to the Centers for Disease Control (CDC), about half of the infants less than 1 year old who get Whooping Cough will be hospitalized. Of those hospitalized, one or two out of 100 will die. Only infants six months or older can be fully vaccinated against the disease, and adults or older children can be carriers for the disease without showing any symptoms.
Parents who turn down vaccinations for their children are often misinformed about the safety and effectiveness of vaccines. “I don’t think people understand that our control of vaccine-preventable diseases such as Whooping Cough and measles is fragile,” Atwell says. “We need to continue to educate people about the implications of not vaccinating their children.”