Vaccine refusal tied to pertussis outbreak

October 02, 2013

Parents refusing to vaccinate their children against pertussis (also known as whooping cough) might have played a role in the deadly 2010 outbreak in California – this according to a new study published in the October issue of Pediatrics.

In 2010, 9,120 cases of pertussis were reported in California, the most since 1947. This new study examines the role of clusters of individuals who refused the vaccine.

The study, “Nonmedical Vaccine Exemptions and Pertussis in California, 2010," analyzes non-medical exemptions for children entering kindergarten from 2005 through 2010, and pertussis cases that were diagnosed in 2010 in California. Researchers identified 39 statistically significant clusters with high rates of non-medical exemptions, and two statistically significant clusters of pertussis cases. Census tracks within an exemption cluster were 2.5 times more likely to be in a pertussis cluster.

With highly infectious diseases like measles and pertussis, it is estimated that more than 95 percent of the population must be immunized to prevent outbreaks and to reduce the risk of the disease for those too young to be vaccinated or unable to receive vaccines. Study authors conclude that communities with large numbers of unvaccinated or under-vaccinated people can lead to pertussis outbreaks, putting vulnerable populations like young infants at increased risk.

From 2000 to 2010, the overall rate of nonmedical exemptions in California rose from 0.77 percent of children entering kindergarten to 2.33 percent. While those rates are still low, researchers noted that some schools reported as many as 84 percent in some cases of new students were exempted in 2010.

The 2010 outbreaks prompted the immediate passage of a new law that made a pertussis booster (Tdap) mandatory for all students in grades seven to 12, starting with the 2011-2012 school year.

In 2012, a bill sponsored by the California Medical Association (CMA) was signed into law that ensures parents make informed decisions about getting their children immunized before they enter school.

Under the bill (AB 2109), sponsored by Sacramento pediatrician and Assemblymember Richard Pan, M.D., a parent seeking an exemption would need to first consult with their physician or other licensed health care professional, who would then sign a form attesting that they had provided information on the benefits and risks of the immunizations, as well as the health risks of the diseases that a child could contract if left unvaccinated.

Previously, California parents could exempt their child from all immunizations by simply signing a standard exemption statement on the back of the California School Immunization Record or provide a separate written statement that proclaims they are exempting their child. No other information or explanation of reason was required.


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