"Holes in the Herd" Linked to Measles Spread

The current measles outbreak across 14 US states indicates that too few individuals are being vaccinated to prevent infections, according to Jason Gallagher, PharmD, FCCP, a clinical pharmacy specialist in infectious diseases at Temple University.

“People who skip vaccines are relying on herd immunity, and this outbreak is showing us what happens when this takes place,” Dr. Gallagher said in an exclusive interview with Pharmacy Times. “The herd is too thin to be effective.”

Many myths and misconceptions surround the measles vaccine, with several originating from Andrew Wakefield’s 1998 study that connected measles, mumps, and rubella (MMR) vaccination with autism. That flawed research resulted in public and high-profile skepticism about vaccine safety, and it is believed to have spurred the modern anti-vaccination movement.

In the time between the study’s initial publication and The Lancet’s 2010 retraction, a number of researchers failed to reproduce Wakefield’s results. Furthermore, the British Medical Journal later discovered that Wakefield falsified his data, either by altering results or participants’ medical histories.

The years of skepticism resulted in robust research proving vaccine safety, but also led to more patients opting out of vaccination—dealing a significant blow to herd immunity.

“There probably isn’t another vaccine with a safety record that has been as explored as the MMR vaccine after the now-retracted paper from the now-unlicensed Andrew Wakefield led to the unfounded concerns about autism associated with MMR,” Dr. Gallagher told Pharmacy Times.

Another common misconception is vaccine failure, or the occurrence of an illness despite being vaccinated against it. According to a February 2012 study published in Vaccine, the phenomenon can occur due to improper vaccination, or when a patient does not develop any or enough protective antibodies after receiving a vaccine. The second case is an extremely rare occurrence in measles vaccinations, though it is sometimes presented as a reason to opt out of vaccination.

“Vaccination against measles is very effective—at least 98%—and the (measles) cases being seen are largely in unvaccinated people,” Dr. Gallagher told Pharmacy Times. “With an infection rate as high as is seen with measles, it’s effectively exposing the ‘holes in the herd.’”

Although the latest measles outbreak is limited in nature, it remains a concern due to pockets of unvaccinated children, according to David T. Bearden, PharmD, Chairman of the Department of Pharmacy Practice at Oregon State University. Dr. Bearden specializes in adult infectious diseases and has researched pharmacist involvement in vaccine-preventable illness.

“The rates of overall vaccinations is encouraging, but the current outbreak highlights the impacts of locally high rates of unprotected children,” Dr. Bearden said in an exclusive interview with Pharmacy Times. “…The same 2014 (US Centers for Disease Control and Prevention) report lists the percentage of patients with vaccine exemptions (as) higher than 5% in several states, including Alaska, Idaho, Maine, Michigan, Oregon, and Vermont. An increase in these rates of unvaccinated children is likely to lead to more outbreak potential.”

Dr. Bearden added that a measles outbreak in the right environment could have disastrous consequences, some of which have already occurred as a result of the latest surge in measles cases.

“It is extremely contagious to an extent that few infectious disease are. Every person infected will spread (the virus) to about 90% of non-immunized contacts,” Dr. Gallagher told Pharmacy Times. “This shows the disastrous potential that can occur in a classroom with non-vaccinated children. My biggest concern is that the virus will infect infants who are too young to be vaccinated. This has already happened in at least 6 cases in the current Disneyland-related outbreak.”

Watch for more measles coverage at PharmacyTimes.com.