Tuesday, March 17, 2015

'Substandard vaccination' blamed for measles outbreak

A group of researchers has attributed the ongoing measles
outbreak to "substandard vaccination compliance" in a
recently published research letter.

Additionally, due to the spread of cases across the US, the
authors state that a significant percentage of the exposed
population could be vulnerable to infection from the disease
due to incomplete vaccination.

"The ongoing measles outbreak linked to the Disneyland Resort in Anaheim, California, shines a glaring spotlight on our nation's growing antivaccination movement and the prevalence of vaccination-hesitant parents," write the authors.

Maimuna S. Majumder, of Boston Children's Hospital and the
Massachusetts Institute of Technology, Boston, and co-authors analyzed publicly available outbreak data from the California Department of Public Health and HealthMap media alerts.

With these data, the authors assessed the influence of
suboptimal vaccination among the population. Their research
letter is published in JAMA Pediatrics.

From January 1 to March 13, 2015, a total of 176 people from
17 different states and the District of Columbia have reported measles infection. The majority of these cases have occurred in California, although some have been reported as far away as New York and Pennsylvania.

The majority of these cases (74%) are associated with the
ongoing outbreak linked to the Disneyland Resort that began in
December 2014. The Centers for Disease Control and Prevention (CDC) state that three other unrelated outbreaks are also currently occurring in Illinois, Nevada and Washington

Vaccination compliance too low to achieve 'herd' immunity

In 2014, a record number of measles cases were reported in the US; the total of 644 cases from 27 different states was the
largest number of cases since measles elimination was achieved
in the US in 2000.

"Given the highly contagious nature of measles, vaccination
rates of 96-99% are necessary to preserve herd immunity and
prevent future outbreaks," the authors write.

However, from their research the authors estimate that vaccination rates among the exposed population could be no
higher than 86%, and potentially even as low as 50%. "This
preliminary analysis indicates that substandard vaccination
compliance is likely to blame for the 2015 measles outbreak,"
they suggest.

"Herd" immunity or community immunity refers to when a
critical proportion of a community is immune to a contagious disease. When a large number of people are protected against a disease, there is little opportunity for it to spread. Containing its spread greatly reduces the risk of individuals who are not immune from catching the disease.

The spread of measles can be prevented with the MMR
(measles, mumps and rubella) vaccine. According to the
CDC, one dose of the MMR vaccine is around 93% effective at preventing the disease if exposed to the virus and two doses are approximately 97% effective.

Many people are not receiving the vaccine, however. The CDC
report that the majority of people infected with measles during the recent outbreak were unvaccinated. In a recent Spotlight article, Medical News Today found that religious beliefs and personal worries that the MMR vaccine is unsafe for children contributed to suboptimal vaccine coverage.

"Clearly, MMR vaccination rates in many of the communities that have been affected by this outbreak fall below the
necessary threshold to sustain herd immunity, thus placing the
greater population at risk as well," conclude the authors.

Recently, MNT reported on a study that suggested the measles
outbreak could become just as devastating in Western Africa as the Ebola virus due to "Ebola-related disruptions to the health care system."