Orenstein WA, Strebel PM, Papania M, Sutter RW, Bellini WJ, Cochi SL.
National Immunization Program, Centers for Disease Control and Prevention,
Atlanta, Ga. 30333, USA.
Measles eradication would avert the current annual 1 million deaths and save
the $1.5 billion in treatment and prevention costs due to measles in
perpetuity. The authors evaluate the biological feasibility of eradicating
measles according to 4 criteria: (1) the role of humans in maintaining
transmission, (2) the availability of accurate diagnostic tests, (3) the
existence of effective vaccines, and (4) the need to demonstrate elimination
of measles from a large geographic area. Recent successes in interrupting
measles transmission in the United States, most other countries in the Western
Hemisphere, and selected countries in other regions provide evidence for the
feasibility of global eradication. Potential impediments to eradication
include (1) lack of political will in some industrialized countries, (2)
transmission among adults, (3) increasing urbanization and population density,
(4) the HIV epidemic, (5) waning
immunity and the possibility of transmission from subclinical cases,
and (6) risk of unsafe injections. Despite these challenges, a compelling case
can be made in favor of measles eradication, and the authors believe that it
is in our future. The question is when.
Estimated susceptibility to asymptomatic secondary immune
response against measles in late convalescent and vaccinated persons.
Damien B, Huiss S, Schneider F, Muller CP.
Laboratoire National de Sante, Luxembourg, Germany.
Serological evidence indicates that
measles virus (MV) could circulate in seropositive,
fully protected populations. Among individuals fully protected against
disease, those prone to asymptomatic secondary immune response are the most
likely to support subclinical MV transmission. The serological
characteristics of protected subjects who developed secondary immune response
after reexposure to measles have been described recently [Huiss et al. (1997):
Clinical and Experimental Immunology 109:416-420]. On the basis of these data,
a threshold of susceptibility was defined to estimate frequencies of secondary
immune response competence in different populations. Among measles, late
convalescent adults (n = 277) and vaccinated high school children (n = 368),
3.2-3.9% and 22.2-33.2%, respectively, were considered susceptible to
secondary immune response. A second vaccination did not seem to lower this
incidence. Even when estimates of symptomatic secondary immune response (e.g.,
secondary vaccine failure) were taken into account, susceptibility to
subclinical secondary immune response was still 5-8 times higher after
vaccination than after natural infection.
Although viral transmission between
protected individuals has never been directly demonstrated, the data describe
a population in which protected but infectious persons could potentially be of
epidemiological importance.
The present article illustrates the extent of secondary vaccine failure after
vaccination for measles, mumps and rubella (MMR). Secondary vaccine failure
means loss of the immunity induced by vaccination to such an extent that
infection becomes possible. Serological investigations carried out with
follow-up periods of up to 16 years after vaccination for measles, 21 years
after vaccination for rubella and 12 years after vaccination for mumps reveal
that loss of antibodies occurs with the elapse of time but that the clinical
significance of this is probably very limited. Where all three types of
vaccination are concerned, secondary vaccine failure has hitherto been very
seldom. Infection with measles after secondary vaccine failure is generally
described as running a milder course. In rare cases, rubella re-infection has
resulted in infection in utero, so that a slight risk of congenital rubella
cannot be entirely excluded after successful vaccination. No extensive
systematic investigations of the effect of revaccination have been carried out
and, similarly, the optimal interval between two or more vaccinations has not
been illustrated in more detail in the literature. Subclinical infection is
not uncommon after all three vaccines. Where measles is concerned, immunity
may possibly be regarded as a continuum which, depending upon the antibody
level, protects the individual from various degrees of clinical disease.
If wild virus can be spread via
individuals with subclinical infections, it is doubtful whether population
immunity (herd immunity), which is necessary to eliminate the three diseases,
can be attained in large
populations.(ABSTRACT TRUNCATED AT 250 WORDS)
Pertussis: herd immunity and vaccination coverage in St
Lucia.
Cooper E, Fitch L.
In a single complete epidemic in St Lucia, an island too small to support
constant clinical pertussis, the pertussis case rates in small communities
(villages and small towns) with differing levels of vaccination coverage of
young children were compared. The association between greater vaccination
coverage and greater herd immunity was clear, despite the imperfect protection
given to individuals. An analysis in
terms of population dynamics is evidence against the theory that endemic
subclinical pertussis maintains transmission in a highly vaccinated
population. We suggest that with a homogeneous vaccination coverage of
80% of 2-year-old children pertussis might be eradicated from the island, and
that this is a practicable experiment.
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MATERIAL CONTAINED, PRESENTED, OR PROVIDED HERE IS FOR GENERAL INFORMATION
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OF THE PUBLISHER, AND IS NOT TO BE CONSTRUED OR INTENDED AS PROVIDING MEDICAL OR
LEGAL ADVICE. THE DECISION WHETHER OR NOT TO VACCINATE IS AN IMPORTANT AND
COMPLEX ISSUE AND SHOULD BE MADE BY YOU, AND YOU ALONE, IN CONSULTATION WITH
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