The Rogues' Gallery

Study - Vaccine Refusal Does Cause Outbreaks

Steven Novella April 5, 2016 6 Comments

That anti-vaccine community, like all ideological communities, has their own narrative and their own facts to support that narrative. Extreme ideological groups tend not to embrace nuance, or accommodate conflicting points – they like to keep their narrative pure. For this reason the anti-vaccine literature is full of scientific claims that are demonstrably wrong: vaccines don’t work, vaccines are not safe, vaccines are not responsible for the decline of infectious illness, and outbreaks are not due to vaccine refusal. Some go as far as to deny the germ theory of disease.

While it may seem obvious that unvaccinated individuals are at higher risk of getting vaccine-preventable diseases, scientists take nothing for granted and always prefer to have hard data to back up their conclusions. To that end, a recent study in JAMA reviews data on measles and pertussis cases and previous studies of these cases.

Regarding measles cases since 2000 (when the disease was declared no longer endemic in the US), they found:

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).

Regarding pertussis they found:

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.

Therefore 59% of those infected with measles were not vaccinated, meaning that the risk of getting measles was much higher in the unvaccinated population. About 92% of the population is up to date on their measles vaccine, which means the unvaccinated are more than 16 times more likely to become infected. Further, outbreaks tended to occur in populations with low vaccine compliance.

The data also shows that unvaccinated populations, because they provide an opportunity for outbreaks to occur, do put the vaccinated population at higher risk.

The picture is similar for pertussis, with the exception that some outbreaks occurred in highly vaccinated populations, implying that immunity wanes as people get older. It is for this reason that booster shots for pertussis are recommended, especially for those who may come into contact with infants.

All of this means that the anti-vaccine narrative is wrong. The data show that the vaccines work in that they provide substantial (if imperfect) protection from these infections. Vaccine refusal dramatically increases the risk of getting measles or pertussis, and puts others at risk as well.

Source: Association Between Vaccine Refusal and Vaccine-Preventable Diseases in the United States
A Review of Measles and Pertussis