++
Measles virus infection is one of the
most important infectious diseases of humans and has caused millions
of deaths since its emergence as a zoonosis thousands of years ago.
Prior to the development and widespread use of measles vaccines,
measles was estimated to cause between 5 and 8 million deaths worldwide
each year. Remarkable progress in reducing measles incidence and mortality
has been made, particularly in sub-Saharan Africa,1,2 as
a consequence of increasing routine measles vaccine coverage and
provision of a second opportunity for measles vaccination through
mass measles vaccination campaigns (called supplementary immunization
activities [SIAs]).3 In the Americas,
intensive immunization and surveillance efforts have stopped endemic
transmission of measles virus, in part based on the successful Pan
American Health Organization strategy of nationwide measles vaccination campaigns
and high routine measles vaccine coverage.4 In
the United States, high coverage with two doses of measles vaccine
has eliminated endemic measles virus transmission. These achievements
attest to the enormous public health significance of measles vaccination.
++
As measles control efforts are increasingly successful, public
perceptions of the risk of measles diminish and are replaced by
concerns of possible adverse events associated with measles vaccine. As
a consequence, numerous measles outbreaks have occurred in communities
opposed to vaccination on religious or philosophical grounds6 or
because of unfounded fears of serious adverse events.7 An
outbreak of measles in San Diego in 2008, imported from Switzerland,
resulted in 11 additional cases in unvaccinated children and two
generations of secondary cases.8 Among the 9 cases
older than 1 year, 8 were unvaccinated because of personal exemption
beliefs. In the first 4 months of 2008, more measles cases were
reported in the United States than any year since 2001, and 63 of
the 64 patients were unvaccinated or had unknown or undocumented
vaccination status.9 Pediatricians can and should
play a role in emphasizing the importance of childhood immunizations and
dispelling myths and misunderstandings.
++
Measles virus is one of the most highly contagious pathogens,
and outbreaks can occur in populations in which less than 10% of
persons are susceptible. Chains of transmission commonly occur among household
contacts, school-age children, and health care workers. There are
no latent or persistent measles virus infections that result in
prolonged contagiousness and no animal reservoirs. Thus, measles
virus can only be maintained in human populations by an unbroken
chain of acute infections, requiring a continuous supply of susceptible
individuals. Newborns become susceptible to measles when passively
acquired maternal antibody is lost and are the main source of new
susceptible individuals. Unvaccinated children contribute to the
pool of susceptibles and to the spread of vaccine-preventable infectious diseases.10
++
When endemic, measles typically has a typical temporal pattern characterized
by yearly seasonal epidemics superimposed on longer epidemic cycles
of 2 to 5 years or more. In temperate climates, annual measles outbreaks
typically occur in the late winter and ...