There are some topics I just have to revisit from time to time. I consider this a public service announcement. So far this year there have been 288 confirmed cases of measles. This is the largest number of cases since endemic measles was declared eliminated from the US. The previous worse year was 2011, which saw 220 cases total.

There is no question that this is tied to vaccine non-compliance. The anti-vaccine movement is scaring people with misinformation and pseudoscience into not vaccinating their children, and as a result we are seeing the return of vaccine-preventable diseases.

When a disease is endemic that means there is a self-sustaining infection – there is always someone infected somewhere and it keeps getting passed around. The MMR vaccine (especially after the second dose was added) resulted in herd immunity, which is a high enough immunity rate so that the infectious disease cannot be passed around indefinitely. High vaccination rates in the US resulted in eliminated measles as an endemic disease by 2000.

Measles cases, and even outbreaks, can still occur, however, by being imported from other countries. Worldwide there are still an estimated 20 million cases per year. In 2012, 122,000 children died from measles. This number is decreasing, due to efforts at worldwide vaccination (now estimated to be at about 84% – good, but not high enough for herd immunity).

Measles cases imported to the US can still lead to outbreaks, especially in populations with low vaccination rates. The CDC reports:

Fifteen outbreaks accounted for 79% of cases reported, including the largest outbreak reported in the United States since elimination (138 cases and ongoing).

Now here comes the important information:

Most of the 288 measles cases reported this year have been in persons who were unvaccinated (200 [69%]) or who had an unknown vaccination status (58 [20%]); 30 (10%) were in persons who were vaccinated. Among the 195 U.S. residents who had measles and were unvaccinated, 165 (85%) declined vaccination because of religious, philosophical, or personal objections, 11 (6%) were missed opportunities for vaccination, and 10 (5%) were too young to receive vaccination.

Most of the measles cases are in people who were not vaccinated, and most of the unvaccinated were those who refused vaccination – and some of those were children whose parents refused on their behalf.

Overall vaccination rates in the US remain high, but there are pockets of low compliance. These occur in communities where anti-vaccine sentiments are common, or even in schools that are friendly to families who do not vaccinate. These low-vaccination pockets can lose their herd immunity, allowing for isolated imported cases to turn into outbreaks.

The conclusion is clear – antivaccine fearmongering is dangerous to the public health. Those who spread such fears should be held accountable, at least in the court of public opinion. I am not talking about honestly raising questions or engaging in discourse, but rather actively advocating against vaccines, fueled by misinformation that can be corrected by honest due-diligence, or even in the face of being corrected by experts.

Such individuals, in my opinion, are guilty of malfeasance and they should be actively marginalized. Meanwhile, the CDC, WHO, and other health organizations, as well as science educators, need to do extra work in order to mitigate the spread of misinformation.