Vaccine refusal is contagious

Research published today in BMC Public Health, which looked at vaccine-related behaviors in California over a 14 year period, finds that non-medical vaccine exemptions operate in a similar way to a contagious disease with cases emanating from high exemption areas. Here, author for the research, Paul L Delamater, tells us about the findings and what they mean in relation to vaccination policies.

Much of the current debate surrounding vaccination in the US centers on parental rights and whether parents should be compelled to vaccinate their children. Hesitancy towards vaccines is not a new phenomenon in the US or elsewhere around the world. Since vaccines were introduced, there has been a subset of the population opposed to them (for a variety of reasons). Modern vaccine hesitancy can likely be traced back to, at least partially, the now debunked research linking the Measles-Mumps-Rubella (MMR) vaccine with autism.

Since there is no federal-level mechanism to compel vaccination, states are responsible for enacting and enforcing their own policies and regulations. Currently, all states except Mississippi, West Virginia, and California provide vaccine hesitant parents with an option to exempt their children from school-entry vaccine requirements for non-medical reasons. Although the details and restrictiveness vary from state to state, non-medical exemptions can be obtained based on parents’ religious, personal, or philosophical beliefs.

A self-reinforcing process

In this case the refusal of vaccines, operated in a manner similar to a contagious disease, geographically spreading from parent to parent or community to community.

We examined how the use of non-medical exemptions changed over a 14-year period in California, a time in which non-medical exemption use more than quadrupled (to over 3% of all incoming kindergarteners in 2013).

As a health geographer, I was very interested in understanding whether vaccine-related behavior, in this case the refusal of vaccines, operated in a manner similar to a contagious disease, geographically spreading from parent to parent or community to community.

We examined how the geographic patterns of non-medical exemption use evolved from 2000 to 2013, as there were no policy changes that would potentially affect parents’ behavior during this time period.

Interestingly, we found evidence of a contagious-like process operating over this time period, as increases in the use of non-medical exemptions appeared to emanate from the initial high use regions over time. Furthermore, we observed that regions with the highest use of non-medical exemptions early in the study period also had the largest increases in use over this time period.

This second finding suggests that vaccine refusal is a self-reinforcing process, e.g., the more people that refuse vaccination in a region, the more acceptable it becomes. These findings are useful to better understand how vaccine refusal can progress from a behavior that is uncommon into one that is largely-accepted (and maybe even expected) in some communities.

Eliminating non-medical exemptions

Given the focus of our research, we did not examine the recent policy changes in California. The state implemented two new laws regarding non-medical exemptions after our study period. AB2109 was implemented prior to the 2014-15 school year, requiring parents to receive counseling from a health care provider prior to obtaining a non-medical exemption. SB277 was implemented prior to the 2016-17 school year and eliminated the non-medical exemption provision entirely.

While SB277 will ultimately increase vaccination rates in California’s schools, the law contained a “Grandfather clause” that allowed students already in school with a valid non-medical exemption to continue attending. This will ultimately delay the law’s intended effect. Furthermore, in the first year the law was in force, medical exemptions more than tripled in incoming kindergarteners.

While California took the bold step of eliminating the non-medical exemption option, other states have yet to follow suit. With the use of non-medical exemptions continuing to rise in many states, we will likely continue to observe reports of vaccine-preventable disease outbreaks,  such as whooping cough, measles, or mumps (and the list goes on).

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