2010 Calif. whooping cough outbreak linked to vaccine-averse parents

Parents who refuse to vaccinate their children may be directly contributing to disease outbreaks, new research suggests.

Researchers have linked parents not vaccinating their children for whopping cough to outbreaks of the disease that occurred in 2010 in California.

They hope their study adds more evidence to convince parents to get their kids vaccinated to not only save their life against this dangerous infection, but to protect children who are most at risk because they're too young to get the shot.

"We live in a free society, but infectious diseases are different from other phenomenon. Someone else's behavior can affect my child or loved one, or me," study author Dr. Saad Omer, an associate professor of global health, epidemiology and pediatrics at Emory University's Vaccine Center in Atlanta, said to HealthDay.

Whooping cough or pertussis is a contagious respiratory infection caused by bacteria that is spread through respiratory secretions like coughing or sneezing in close quarters. Symptoms include uncontrollable, violent coughing that makes it hard for the patient to breath. People cough until the air is gone from their lungs and make a "whooping sound" when trying to take deep breaths, hence the diseases' nickname.

For the study, researchers analyzed all the non-medical exemptions for kids entering kindergarten from 2005 through 2010 in the state of California.

Some children are unable to get the recommended vaccines because of allergies or other medical conditions that weaken their immune systems, like some childhood cancers. Non-medical exemptions could include religious or personal beliefs.

The researchers matched this exception list to the number of pertussis cases diagnosed during the 2010 outbreak. In 2010, the state experienced his highest number of whooping cough cases in more than 60 years, with more 9,000 cases including 809 hospitalizations and 10 deaths reported, a Dec. 2012 Journal of Pediatrics review of the outbreak found.

California tightened non-medical vaccine exemption rules in 2012 following the state's whooping cough outbreak, Nature reported.

The researchers flagged 39 clusters of high rates of non-medical exemptions, and two whooping cough disease clusters. A closer look showed people in the exemption cluster were about 2.5 times more likely to be in the whooping cough cluster. Whooping cough is a highly contagious disease, the researchers point out, which could spell trouble in an unvaccinated cluster.

The study did not look specifically at the reasons for why parents were refusing vaccines, but the researchers found the families were more likely to be of high socioeconomic status.

The new research was published Sept. 30 in Pediatrics.

The U.S. vaccine for whooping cough is the DTaP vaccine, which also protects against diphtheria and tetanus. Five vaccines are recommended at the following ages: 2, 4 and 6 months of age, between 15 and 18 months and then before a child enters school at 4 to 6 years old. That means very young children could risk serious disease in the time before they're vaccinated.

A Sept. 9 study in JAMA Pediatrics found that young kids under 36 months of age who are not up-to-date on their pertussis vaccines are at higher risk of getting whooping coughcompared to those who have gotten the appropriate number of shots.

An Aug. 1 report from the Centers for Disease Control and Prevention (CDC) estimated about 95 percent of kindergartners got a DTaP vaccine heading into the 2012-2013 school year, but the health agency reported worrisome exemption rates.

Recent research suggests the vaccine's effectiveness could wane after young people got the last of the five recommended doses at age 6, leading doctors to urge a booster dose between 11 or 12 years old.

"After about five years the immunity is significantly less, and so, that's why we want to continue immunization at about every five to 10 years," Dr. Wilbert Mason, a pediatric infectious disease specialist at Children's Hospital Los Angeles, said to CBS News' Bigad Shaban.

All adults are urged to get a whooping cough vaccine as well.

Texas is currently fighting a whooping cough epidemic, and officials said last month the state was on track to have the highest number of cases recorded in over 50 years.

Health officials have also seen increases in rates of another vaccine-preventable disease, measles, which they blame on anti-vaccination beliefs

"Clusters of people with like-minded beliefs leading them to forgo vaccines can leave them susceptible to outbreaks when measles is imported from elsewhere," Dr. Anne Schuchat, director of the CDC's National Center for Immunization and Respiratory Diseases, told reporters Sept. 12 during a press conference announcing the study's results. Similarly to the new research, the CDC's study looked at earlier measles outbreaks to find a link between vaccine-refusing parents.

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