Friday, 30 November 2007
BCG Booster dose needed to fight TB
Published in Deccan Chronicle on November 30, 2007
By Syed Akbar
Hyderabad, Nov 29: City scientists suggest that a booster dose of BCG vaccine should be given to children between the age of 13 and 15 years to prevent spread of tuberculosis in the country.
The Centre for DNA Fingerprinting and Diagnostics and Mahaveer Hospital and Research Centre took up a study to find out why people, who had been immunised for TB in childhood, were developing the killer disease at a later stage in life. The study revealed that the efficacy of the BCG vaccine comes down with age, necessitating a booster dose during the adolescent period.
Those who do not take a booster BCG vaccine stand exposed to the attack of the TB bacteria.
Mycobacterium bovis BCG vaccine has displayed inconsistent efficacy in different trials conducted in various geographical regions. Though BCG has brought down the instances of TB in children, its efficacy wanes with age, causing concern to health experts and researchers. The present study employed the latest laboratory techniques to establish that a single dose of BCG vaccine given at birth is not effective throughout the life of an individual. He or she needs a booster dose, preferably in the adolescent or teenage to prevent the spread of the disease.
Ninety healthy children who were without any clinical evidence of tuberculosis, 45 with a BCG-scar and the remaining 45 without scar and 25 with tuberculosis were covered in the study. The incidence of TB was analysed in 216 children attending a DOTS clinic in Hyderabad.
High incidence of TB was observed in age group 13-14 years followed by children in the age group 10-12 years. In all 79 per cent of vaccinated children showed positive proliferative responses while only 39 per cent of the unvaccinated and 58 per cent of the tuberculosis children showed positive responses.
The stimulation indices in vaccinated children decreased in the older children concurring with an increase in the incidence of TB.
"Significantly high levels of in vitro interferon demonstrated in BCG vaccinated children substantiate the observation that BCG is effective in children, but the effect may wane with age. The immunity could be boosted using modified BCG," the study pointed out.
Though a variety of live vaccines have been developed as vaccines, until now no booster vaccine has been shown capable of significantly enhancing the level of protective immunity.
The study noted that waning of immunity was of particular public health interest because it may result in increased susceptibility later in life. The mechanism underlying the gradual loss of effectiveness of BCG as the individual reaches 10 to 15 years of age is poorly understood.
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