Basis for deciding cost effectiveness of TB vaccination programmes questioned

Current risk assessment methods, which are used to inform the timing and extent of tuberculosis (TB) vaccination programmes, may overestimate the real risk of contracting the disease up to threefold, reveals research in Thorax.

The findings have prompted a leading expert to question the validity of the ways in which decisions are made as to whether TB vaccination programmes, such as those offered to 13 and 14 year olds in the UK, are cost effective

Researchers analysed the results of tuberculin skin tests in 21,000 children aged between 6 and 9 years in Hong Kong, where all newborn babies are routinely vaccinated against TB.

Tuberculin tests use injectable TB antigens to assess whether a person has ever been exposed to the bacteria that cause the infection, based on the extent of the ensuing skin reaction. They cannot, however, measure how long a person has been infected, or whether the infection is active, and can therefore be passed on to others.

The results were fed into three different approaches in a bid to estimate the subsequent annual risk of TB infection.

The first approach relied on the extent of the skin reaction and the age of the child; the second approach compared positive test results in two age groups?6 to 7 year olds and 8 to 9 year olds; and the third concentrated on the size of the skin reaction, referred to as the "secondary peak."

The first and second approaches are routinely used to calculate the probable cost effectiveness of mass TB vaccination programmes.

But the estimates they produced were around three times higher than the estimate produced by the third method, which agreed best with the expected rates, based on levels of active TB disease reported.

Writing in the journal, Dr John Moore-Gillon, of the Department of Respiratory Medicine, St Bartholomew's and the Royal London Hospitals, comments: "?the results suggest that the actual risk of tuberculous infection may be lower than that implied by conventional methods."

He continues: "This may influence decisions about the cost effectiveness of mass BCG vaccination programmes, such as that currently offered to 13-14 year olds in the UK."

Dr Moore-Gillon also points out that despite the fact that TB is a growing problem, it is given low priority by funding bodies and politicians. The assessment methods are 50 years old, and little importance is afforded to discovering new diagnostic techniques or more effective vaccines.

"there has been a comprehensive failure on the part of the political and medical establishment to invest adequately in research into one of the leading infectious threats to global health."