California’s worst episode of whooping cough, or pertussis, in 2010, likely spread among unvaccinated children to infect 9,210 youngsters.
At first, the outbreak was blamed on waning immunity to the whooping cough vaccine, but new research published in the journal Pediatrics reports that the high number of children who were intentionally unvaccinated also contributed to the rapid spread of the infection.
In recent years, a small but vocal group of parents have decided to either limit the number of vaccines their children receive, or to not immunize their children at all according to recommended national guidelines. Some are concerned about ‘vaccine load,’ and believe that their infants’ still-developing immune systems can get overwhelmed by multiple shots that they receive during one visit to the pediatrician. Others continue to doubt the safety of the immunizations themselves, worried about a connection between the vaccines and a higher risk of autism. But none of these reasons are supported by solid scientific evidence; recent studies showed that receiving several vaccines on a single day was not associated with a higher risk of autism, and the researcher responsible for raising the alarm about shots and autism was discredited.
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Parents opting out of vaccinations concerns public health officials since in addition to the pertussis outbreaks, there are hints that measles cases may also be rising due to parental vaccine refusals. While national childhood immunization rates are good overall, at around 90%, Nina Shapiro, a professor at the David Geffen School of Medicine at University of California Los Angeles, crystallized the worry over unvaccinated kids in an op-ed in the Los Angeles Times :
Private schools vary widely, but some have rates of less than 20%. Yes, that’s right: Parents are willingly paying up to $25,000 a year to schools at which fewer than 1 in 5 kindergartners has been immunized against the pathogens causing such life-threatening illnesses as measles, polio, meningitis and pertussis (more commonly known as whooping cough). In order for a school to be considered truly immunized, from a public health standpoint, its immunization rate needs to be 90% or higher.
The researchers of the Pediatrics study compared the number of intentionally unvaccinated children who entered kindergarten from 2005 to 2010 to the onset of the whooping cough outbreak in 2010. They were able to identify 39 regional clusters of kids with non-medical reasons for being unvaccinated, and two clusters that were significantly related to rapid spread of whooping cough. Children who are intentionally not vaccinated and become infected with diseases like measles or pertussis, can pass the illness on to those who can’t be immunized, such as babies under six months and those with compromised immune systems, such as cancer patients.
The authors hope that the results of their study reaffirm the harms that intentionally not immunizing children can bring — not only to the unvaccinated but to those around them as well.