According to a new study the proportion of medical exemption for vaccines kindergartners increased sharply after California had abolished personal-belief exemption. The study hints at the parents who do not want to immunize have perceived doctors who are willing to offer medical exemptions for students – a possible trend that may weaken the mutual patronage against infectious diseases that the state law sought to reinforce.

At the time of enlisting, the students have to show the evidence that they were immunized against diseases such as polio, chickenpox and measles, harmful infection that can disseminate quickly. Students can be exempted from the pre-condition if they have medical issue that stops them from getting immunized. For example Pediatric cancer has established detrimental reactions to immunization. However, in many states parents can also get exemptions based on personal ideology.

California senate bill passed in 2015 eliminated personal-belief exemptions – a step that came into action during 2014 measles outbreak that emanated at Disneyland. That outbreak was likely aggravated by low vaccination rates, an earlier analysis found.

California’s law need to eliminate personal-belief exemptions so vaccination rates can be increased which could improve the herd immunity the allied protection offered when the enormous majority of individuals in a group are resistant to a disease. Herd immunity aides those who due to medical causes cannot be immunized and are powerless to infections.

Therefore SB 277 performed as a natural experiment. It enabled researchers to observe what happened to immunization rates prior to and after the law’s passage. Would parents averse to vaccines turn to medical exemptions since they could no longer accrue personal belief exemptions?