Researchers have blamed the rising incidence of whooping cough in recent decades on a myriad of factors, from the weaknesses of acellular vaccines to parents' decisions to delay immunizations. Fully reversing the trend will likely involve multiple factors too, but lawmakers could begin the process with one action--tightening rules on nonmedical exemptions from vaccinations.
Last year's measles outbreaks among Jewish communities in New York and a church in Texas showed how clusters of people who skip vaccinations on religious grounds are vulnerable to disease. A team of U.S. researchers has now quantified how big an impact a state's exemption laws--which range from allowing kids to skip vaccines on philosophical grounds to only accepting medical reasons--have on the incidence of disease. For rare infections like hepatitis B, there is no correlation.
However, states with laxer laws on vaccine exemptions were found to have higher rates of whooping cough. If every state raised its restrictions by one level--for example by banning philosophical exemptions but still allowing religious reasons--cases of whooping cough would fall by more than 1%. In contrast, a 1% increase in uptake of the tetanus, diphtheria, pertussis (Tdap) vaccine that protects against whooping cough is predicted to cause just a 0.04% drop in annual cases.
The effect of maintaining the status quo was seen in California, which suffered 1,699 cases of whooping cough last year, up 63% on 2012, The Sacramento Bee reports. Nationwide, there were 48,000 cases. Counties in which a lot of parents opted out of vaccines were particularly badly affected. More parents in Nevada County refuse vaccines for their kids than in any other part of California. It also suffered the biggest year-on-year increase in whooping cough cases, which rose 1300% to 70.