The JAMA Network Journals
An analysis of numerous studies and reports finds that
unvaccinated or undervaccinated individuals comprised substantial proportions
of cases in measles and some pertussis outbreaks, and vaccine refusal was
associated with an elevated risk for measles and pertussis, including among
fully vaccinated individuals, according to a study appearing in the March 15
issue of JAMA.
Recent outbreaks of vaccine-preventable diseases in the United
States have prompted clinicians, public health officials and the public to pay
greater attention to the growing phenomenon of vaccine refusal and hesitancy.
Improved understanding of the association between vaccine refusal and the
epidemiology of these diseases is needed.
The
authors searched the medical literature for reports of U.S. measles outbreaks
that have occurred since measles was declared eliminated in the United States
(after January 1, 2000), endemic and epidemic pertussis since the lowest point
in U.S. pertussis incidence (after January 1, 1977), and for studies that
assessed disease risk in the context of vaccine delay or exemption.
The researchers identified 18 published measles studies, which
described 1,416 measles cases (individual age range, 2 weeks-84 years; 178
cases younger than 12 months) and more than half (57 percent) had no history of
measles vaccination.
Of the 970 measles cases with detailed vaccination data,
574 cases were unvaccinated despite being vaccine eligible and 71 percent of
these had nonmedical exemptions (e.g., for religious or philosophical reasons,
as opposed to medical contraindications; 42 percent of total).
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 percent-45 percent) of unvaccinated or undervaccinated individuals.
However,
several pertussis outbreaks also occurred in highly vaccinated populations,
indicating waning immunity. Nine reports (describing 12 outbreaks) provided
detailed vaccination data on unimmunized cases; among 8 of these outbreaks,
from 59 percent through 93 percent of unvaccinated individuals were
intentionally unvaccinated.
"This review has broad implications for vaccine practice
and policy. For instance, fundamental to the strength and legitimacy of
justifications to override parental decisions to refuse a vaccine for their
child is a clear demonstration that the risks and harms to the child of
remaining unimmunized are substantial. Similarly, central to any justification
to restrict individual freedom by mandating vaccines to prevent harm to others
is an understanding of the nature and magnitude of these risks and harms.
However, the risks of vaccine refusal remain imperfectly defined, and the
association between vaccine refusal and vaccine-preventable diseases may be both
population- and disease-specific," the authors write.
Editorial: Toward High-Reliability Vaccination Efforts in the
United States
"Without a centralized infrastructure focused on the goal
of maximizing community immunity, high-reliability vaccine coverage remains
challenging in the United States," writes Matthew M. Davis, M.D.,
M.A.P.P., of the University of Michigan, Ann Arbor, in an accompanying
editorial.
"Nonetheless, if vaccines are developed for emerging
diseases that threaten the U.S. population--such as Zika, Ebola, or human
immunodeficiency virus--the public will likely expect the currently complex and
heterogeneous vaccination system in the United States to function as a seamless
organization. The U.S. population wants vaccination to be safe, effective and
available in a timely manner, and for immunization to be durable. Current
challenges with measles and pertussis outbreaks provide an opportunity to
develop and evaluate approaches to achieve unprecedented levels of vaccination
coverage, limit waning immunity, and minimize vaccine-preventable disease for
children and adults alike."