POST 01026E : T SERIES VACCINE EFFICACY
Follow-up on Post 01021E
16 December 2006
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After a short comment by Michel Zaffran
(mailto:[email protected]), Jos Vandelaer
(mailto:[email protected]) from UNICEF/WHO replies to Jedeth Mamora
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The tetanus module of the serie on immunological basis for
immunization is indeed the best reference.
Michel Zaffran
GAVI Alliance
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The moderator is correct: the "Immunological Basis of Immunization
(module 3)" gives a good overview of duration of protection and
issues involved. An updated version of this document is being
finalized and will be published in the coming months and will provide
additional information.
Nevertheless, quite a number of issues remain unclear when it comes
to duration of protection. That is partly because the studies that
have looked at this are often difficult to compare (e.g. they are
based on different schedules, different intervals between doses,
different ages at which the vaccine is given, different vaccines,
different serology tests used to measure antitoxin levels etc. ), but
also because "protection" is a relative notion. Although there is
general consensus that antitoxin levels of 0.01 IU/ml are required to
provide protection, this "cut-off" is not so absolute, and whether
someone is protected will also depend on the "attack load" with
tetanus toxins. Needless to say that all this makes interpretation of
data on duration of protection difficult.
WHO has tried to provide countries with some guidance on duration of
protection: see the WHO document "Core Information for the
development of immunization policy" (Table 7) (available at
http://www.who.int/vaccines-documents/DoxGen/H3DoxList.htm.). The
duration of protection in that table is considered the minimum
duration, and often duration may actually be longer.
WHO has traditionally focused on strategies aimed at preventing
maternal and neonatal tetanus, and is therefore recommending
TT-containing doses in pregnancy or among women of child bearing age.
(see table 7 in the "Core Information"). However, recognizing that
also tetanus in other age groups needs to be prevented, and in order
to address the situation that more and more young adults have now
been immunized in childhood with DTP, WHO is recommending booster
doses around school-entry age, adolescence and in early adulthood.
Please refer to the WHO position paper on tetanus, published earlier
this year
(http://www.who.int/immunization/documen ... index.html ).
In the end it is up to individual countries to adopt a schedule to
fits their needs best. There are therefore different ways that
countries use to ensure their population is protected against
tetanus. A number of countries may use a 5-yearly or 10-yearly
booster dose, while others use a school-based approach, or
post-trauma immunization to provide boosters.
For further links to tetanus-related documents, you can also visit
the following site:
http://www.who.int/immunization_monitoring/diseases/MNTE_resources/en/index.html
I hope this helps. Best Regards,
Jos Vandelaer
UNICEF Sr Project Officer,
based in WHO Geneva
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