Tuberculosis remains a leading cause of death from any single infectious disease, accounting for over a quarter of all avoidable deaths. It infects about 1 billion people and causing an estimated 1–2 million deaths annually [1
]. Nearly 3–4 million children in India have tuberculosis while 94 million are at risk to infection. 40% of these children by the age of 6 yrs and 80% by the age of 16 years are labeled as infected [2
Bacillus Calmette-Guerin (BCG) vaccine, which consists of live attenuated Mycobacterium tubercle bovine Danish 1331 strain, has been extensively used as a protective measure against tuberculosis for the last half century.
Under Universal immunization Programme (UIP), primary BCG vaccination is given at birth or within the first month. The attenuated bovine non-pathogenic Mycobacterium induces tuberculin sensitivity and potentates the defense mechanism enabling the recipient to combat re-infection when exposed to pathological strains of mycobacterium later. This primary infection enables the vaccinated person to mobilize immune processes more rapidly when challenged by further natural infections.
A definite scar evidences an effective BCG vaccination and absence of this denotes that no immunity is attributable to the vaccination [14
]. However, even with proper vaccination the immunity has been observed to decline within a few years, on the basis on which revaccination at five years has been suggested as an optional dose by the Indian Academy of Pediatrics [6
]. Vijayalakshmi et al[11
] suggested that revaccination may be contemplated after 8 years.
BCG given as a diagnostic test is based on Koch's phenomenon. When BCG is given to a child with tuberculosis, the reaction occurs at the site of vaccination within 48–72 hrs as against the usual late reaction i.e. after 3–6 weeks in child without tuberculosis. The reaction is measured with a standard plastic scale and the maximum size of the reaction is noted. The appearance of papule or induration more than 5 mm in size at the test site is considered as positive BCG Test [7
BCG Test response is graded as mild (5–10 mm), moderate (10–20 mm) or severe (more than 20 mm) [6
]. The reaction is complete if all the stages i.e. papule, pustule, ulcer and scab are seen, but is incomplete when only a papule or nodule is seen and the reaction does not progress to a stage of pustule or scab formation.
BCG response is more sensitive than the Mantoux test (Tuberculin test) and hence has been considered a better tool for epidemiological investigations. However, the effect of previous BCG vaccine on the subsequent revaccination is not well established and only a few elaborate studies have been carried out in this regard. It has been seen that the Mantoux test is not reliable as a post-vaccination check, because in vitro, cell-mediated immune responses may be demonstrable even when Mantoux test becomes negative [11
The response of BCG may be different in previously vaccinated children and needs to be considered before interpreting positivity. The exact type of reaction and range of induration is not clear cut or well established.
There is possibility of over diagnosis of tuberculosis on the basis of BCG Test results, if previous BCG vaccination status is not taken into consideration. It is to be noted that the BCG Test may be positive in previously vaccinated children even when Mantoux test is negative.
This study has been carried out to determine the pattern of BCG reaction comparing previously vaccinated with non-vaccinated children.
Aims and objectives
1. To assess the BCG skin reaction in Mantoux-negative healthy children at 4–6 years of age previously vaccinated with BCG, as evidenced by the presence of scar [14
2. To compare the reaction between children with and without previous BCG scar.