Reuters Health - Parents who delay or skip childhood vaccinations even when kids have no medical reason to avoid their shots are contributing to U.S. outbreaks of measles and pertussis, a research review suggests. 
 
 A vial of measles, mumps and rubella vaccine and an information sheet is seen at Boston Children's Hospital in Boston, Massachusetts February 26, 2015. REUTERS/Brian Snyder 
 
 More than half of 1,416 measles cases reported in the U.S. since the disease was declared eliminated in 2000 were for people with no history of measles vaccination, the analysis found. 
 
 Among more than 10,000 pertussis patients with known vaccination status, 24 to 45 percent of people in the five largest statewide epidemics since 1977 were unvaccinated or only partially vaccinated, the analysis also found. 
 
 “If there are a high number of susceptible or unvaccinated individuals in the community the risk of getting infected – even for vaccinated children – goes up,” said senior study author Dr. Saad Omer, a pediatrics and epidemiology researcher at Emory University in Atlanta. 
 
 That’s because few vaccines are 100 percent effective, Omer added by email. 
 
 With pertussis, or whooping cough, up to 2 percent of people who receive all five recommended vaccine doses on time may still get this bacterial infection of the lungs, according to the U.S. Centers for Disease Control and Prevention. 
 
 For measles, roughly 3 percent of people who receive both recommended doses of the vaccine may still get the virus, according to the CDC. 
 
 These numbers are a best case scenario, assuming that only people with medical reasons – like certain cancer treatments, rare allergies to vaccine ingredients, or diseases that compromise the immune system – forgo inoculations. 
 
 But the CDC reports that fewer than 1 percent of kids need to skip vaccines for medical reasons, based on data from Mississippi and West Virginia, states that only grant exemptions under these circumstances. 
 
 Instead, Omer and colleagues found that the majority of measles and pertussis cases in the outbreaks they analyzed were due to people intentionally skipping vaccinations. 
 
 Among 970 measles cases with detailed vaccination data, 574 cases were unvaccinated people who were eligible to receive their shots, researchers report in the Journal of the American Medical Association. 
 
 Most of these unvaccinated people – 405 of them – had nonmedical reasons for skipping vaccinations such as religious or philosophical objections, the analysis found. 
 
 For the subset of pertussis reports from outbreaks with detailed data on unvaccinated individuals, 59 to 93 percent of cases were for people who intentionally skipped their inoculations, the analysis also found. 
 
 Several pertussis cases also cropped up in highly vaccinated communities, suggesting waning immunity against the disease, the researchers note. 
 
 Limitations of the study include a focus on measles and pertussis in the context of vaccine exemption rates, which may have underestimated the disease risk associated with skipping vaccines, the authors point out. 
 
 Nonmedical exemptions also don’t explain all of the resurgence in measles and pertussis in recent years, Dr. Matthew Davis, a pediatrics researcher and deputy director of the Institute for Healthcare Policy and Innovation at the University of Michigan in Ann Arbor, noted in an editorial. 
 
 “It is very difficult to put a specific number on how much vaccine refusals reduce a community’s protection against disease,” Davis said by email. 
 
 “What this latest comprehensive review illustrates is that individuals who refuse vaccines not only put themselves at risk for disease,” Davis added. “It turns out that they also put others at risk too – even people who have been vaccinated before, but whose protection from those vaccinations may not be as strong as it used to be.” 
 
 SOURCE: bit.ly/1Rj5JhT JAMA, online March 15, 2016. ||||| Importance Parents hesitant to vaccinate their children may delay routine immunizations or seek exemptions from state vaccine mandates. Recent outbreaks of vaccine-preventable diseases in the United States have drawn attention to this phenomenon. Improved understanding of the association between vaccine refusal and the epidemiology of these diseases is needed. 
 
 Objective To review the published literature to evaluate the association between vaccine delay, refusal, or exemption and the epidemiology of measles and pertussis, 2 vaccine-preventable diseases with recent US outbreaks. 
 
 Evidence Review Search of PubMed through November 30, 2015, for reports of US measles outbreaks that have occurred since measles was declared eliminated in the United States (after January 1, 2000), endemic and epidemic pertussis since the lowest point in US pertussis incidence (after January 1, 1977), and for studies that assessed disease risk in the context of vaccine delay or exemption. 
 
 Findings We identified 18 published measles studies (9 annual summaries and 9 outbreak reports), which described 1416 measles cases (individual age range, 2 weeks-84 years; 178 cases younger than 12 months) and more than half (56.8%) had no history of measles vaccination. Of the 970 measles cases with detailed vaccination data, 574 cases were unvaccinated despite being vaccine eligible and 405 (70.6%) of these had nonmedical exemptions (eg, exemptions for religious or philosophical reasons, as opposed to medical contraindications; 41.8% of total). Among 32 reports of pertussis outbreaks, which included 10 609 individuals for whom vaccination status was reported (age range, 10 days-87 years), the 5 largest statewide epidemics had substantial proportions (range, 24%-45%) of unvaccinated or undervaccinated individuals. However, several pertussis outbreaks also occurred in highly vaccinated populations, indicating waning immunity. Nine reports (describing 12 outbreaks) provided detailed vaccination data on unimmunized cases; among 8 of these outbreaks from 59% through 93% of unvaccinated individuals were intentionally unvaccinated. 
 
 Conclusions and Relevance A substantial proportion of the US measles cases in the era after elimination were intentionally unvaccinated. The phenomenon of vaccine refusal was associated with an increased risk for measles among people who refuse vaccines and among fully vaccinated individuals. Although pertussis resurgence has been attributed to waning immunity and other factors, vaccine refusal was still associated with an increased risk for pertussis in some populations.
– Wondering what's behind recent outbreaks of measles and whooping cough in the US? Perhaps not surprisingly, a new study published in JAMA finds that people who don't vaccinate—for non-medical reasons—contribute to the problem, Reuters reports. Since measles was declared eliminated in the US in 2000, there have been 1,416 cases of the disease reported, and the study finds that more than half of those cases were in people who hadn't been vaccinated for measles. Detailed vaccination data was available for 970 of the measles cases, and 405 of them involved people who skipped vaccinations without a medical reason to do so. Researchers also looked at more than 10,000 cases of whooping cough in patients with known vaccination status and found similar, though somewhat less dramatic, results. In the pertussis cases, when looking at the five biggest statewide epidemics since 1977, 24% to 45% of the people affected were completely or partially unvaccinated. And in looking at the pertussis cases for which detailed vaccine data was available, 59% to 93% of cases were in people who were intentionally unvaccinated (as opposed to unvaccinated for medical reasons.) “If there are a high number of susceptible or unvaccinated individuals in the community the risk of getting infected—even for vaccinated children—goes up," says the study's senior author, because most vaccines are not 100% effective. Up to 2% of people who are fully vaccinated for pertussis and 3% of people who are fully vaccinated for measles are still at risk of getting the disease. Non-medical vaccine exemptions don't fully explain the resurgence of measles and whooping cough (researchers also found evidence of waning immunity against pertussis, for example), but another researcher says the study finds that "individuals who refuse vaccines not only put themselves at risk for disease," but others too.