Mumps is on the rise and it may be because the immune response to the vaccine has weakened over time or the virus has evolved.
The rise in the mumps virus has largely been in the young adult population, ages 18-29. Most of these people have received the recommended two shots during early childhood.
The data from epidemiological studies and mathematical models allowed researchers to discover that the ongoing resurgence that started in 2006 has left one-third of the children ages 10-14 at risk. According to researchers, 25 percent of those vaccinated will lose their immunity in eight years. Fifty percent will lose immunity in 19 years and 75 percent in 38 years. The study was published in Science Translational Medicine.
There have been outbreaks of mumps in vaccinated populations, according to Joseph A. Lewnard, who is a research associate at the Harvard T.H.Chan School of Public Health. However, measles have only been seen among unvaccinated populations.
Currently, a third shot is being recommended during outbreaks, but new studies must be conducted to know if it will limit future outbreaks.
The increased cases of mumps among vaccinated populations within the United States has been consistent over the past 10 years and it has casted doubts about the efficacy of the vaccine.
Lewnard and his team have examined the outbreaks using the effectiveness data and dynamic transmission modeling. It was learned that the increase in cases of the mumps is consistent with the loss of vaccine protection over time. A third dose could possibly extend protection. If this is true it will be useful in creating a clinical action plan that will prevent the spread of the virus.
The United States and other vaccinated countries have experienced the resurgence after decades of declining incidence of the mumps. Outbreaks among vaccinated individuals in vaccinated areas have raised concerns about the effectiveness of the inoculation currently in use. It is possible that the shot is not strong enough to adequately protect against the most current strain of the mumps.
Data that has been synthesized from six different studies about the effectiveness of the mumps vaccine indicate that the protection begins to wane after 27 years.
Once scientists accounted for the waning, there was “no evidence that the emergence of heterologous virus genotypes contributed to changes in vaccine effectiveness over time.” The outbreaks among young adults since 2006 were compared with the outbreaks in the late 1980s and early 1990s and proved that they aligned with susceptibility of the age groups, points to a loss of vaccine-derived protection.
If it were the evolution of the strain of the mumps, it would be more likely to cause more cases in children instead of young adults. A routine does at 18 or a booster throughout adulthood may be a strategy to prevent the resurgence of the mumps, but it needs to be assessed in clinical trials.
By Jeanette Smith
The New York Times: Mumps Is On the Rise. A Waning Vaccine Response May Be Why.
Science Translational Medicine: Vaccine waning and mumps re-emergence in the United States
Image Courtesy of Dr. Partha Sarathi Sahana’s Flickr Page – Creative Commons License