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ASSESSMENT OF POST-VACCINATION ALLERGY AMONG THOSE
BCG VACCINATED WITHOUT PRE-VACCINATION TUBERCULIN TEST |
Kul Bhushan, SS Nair & KT Ganapathy: Indian
J TB 1970, 17, 18-31. |
The conventional methods of assessment of post-vaccination
allergy by doing tuberculin testing among the vaccinated group are
inapplicable in case of BCG vaccination without prior tuberculin
test (Direct BCG). Because of obvious technical and operational
advantages of direct BCG vaccination a search for a method of technical
assessment of BCG vaccination is important. Hence, a study was
carried out by the BCG Assessment Team of National Tuberculosis
Institute in Tumkur district of Mysore state where Mass BCG Campaign
was going on. Four groups of persons aged 0-20 years, each group
belonging to two BCG Technicians area and vaccinated one day prior
to visit of assessment team, were randomly selected. Besides, persons
(0-20 years) from 2 unvaccinated villages of adjacent area were
included as control groups. All persons were registered simultaneously
tuberculin tested with 1 TU RT 23 and 5 TU RT 22 within 24
hours of BCG vaccination (for pre-vaccination allergy) and retested
with tuberculin 5 TU RT 22 at the end of 3 weeks and 3 months (for
post-vaccination allergy). The four vaccine groups were vaccinated
with vaccine batch Nos. 977, 978, 981 and 984 respectively. Classification
of the directly vaccinated persons into previously infected and
non-infected by tuberculin test administered within 24 hours of
vaccination and about 12 weeks later, elicitation of post-vaccination
allergy only among the non-infected, has been considered as the
Reference Test for judging the suitability of other methods of assessment
studied. The main findings are: (1) The Reference Test showed that
the four batches of BCG vaccine used had induced varying levels
of allergy. (2) Assessment based on the mean size of post-vaccination
reactions among 0-4 years age group, which consists predominantly
of previously non-infected persons, showed a different pattern of
differences between the four batches of vaccine as compared to the
Reference Test. Moreover, to get adequate number of children aged
0-4 years, it will be necessary to cover a comparatively large population.
(3) The method of using the mean size of post-vaccination reactions
among those classified as non-infected on the basis of vaccination
reactions of size 0-13 mm at the site of BCG vaccination on the
4th day of vaccination showed results similar to the Reference Test.
But this method has only a marginal operational advantage over the
Reference Test. (4) Using size of induration at the site
of vaccination on 21st day of vaccination did not give the same
results as the Reference Test. Operationally this method would have
been most suitable as it involved only one visit to the group. (5)
Differences between mean size of post-vaccination tuberculin reactions
among directly vaccinated persons and mean size of (natural) allergy
in reactors among neighbouring unvaccinated areas showed the same
results as the Reference Test. This method has the operational advantage
but needs further investigations. (6) Tuberculin testing of all
directly BCG vaccinated persons including the natural reactors about
12 weeks after vaccination compared favourably, with the reference
method, as the tuberculin reactors contributed less than 1 mm over
and above the allergy in the vaccinated non-reactors . This method
would be useful when rate of tuberculin reactors is less than 20%
in 0-20 years age group and their mean size is also less than 20
mm. Operationally, it is a simpler method next only to No.4 above.
Further investigations are considered necessary for final selection
of this or any of the other methods.
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KEY WORDS: BCG, POST-VACCINATION ALLERGY, ASSESSMENT,
DIRECT BCG VACCINATION. |