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The World Health Organization estimates that roughly 2 billion people – nearly 1 in 3 – are infected with the TB bacilli, and of those, 1 in 10 will develop active TB during his or her lifetime.
The incidence of Tuberculosis varies greatly around the world, with North America, Europe and Australia/New Zealand seeing the lowest rates, and with the highest rates found in Africa, India, and Asia.
(From Global TB Control Report 2010)
With growing instances of MDR-TB (multi-drug resistant tuberculosis), and XDR-TB (extensively drug resistant Tuberculosis) and perhaps even The Emergence Of `Totally Resistant TB’ the need has never been greater to find a way to prevent infection.
A vaccine against TB called BCG (Bacillus Calmette-Guérin) was developed in the 1920s, but only gained wide usage after World War II. While deployed in many countries (but never routinely in the United States), its efficacy is limited.
The World Health Organization released a position paper on the use of BCG in 2004, where they discuss its use and limitations against Mycobacterium tuberculosis (Mtb), the etiological agent of tuberculosis (TB).
The bacille Calmette–Guérin (BCG) vaccine has existed for 80 years and is one of the most widely used of all current vaccines, reaching >80% of neonates and infants in countries where it is part of the national childhood immunization programme.
BCG vaccine has a documented protective effect against meningitis and disseminated TB in children.
It does not prevent primary infection and, more importantly, does not prevent reactivation of latent pulmonary infection, the principal source of bacillary spread in the community.
The impact of BCG vaccination on transmission of Mtb is therefore limited.
In short, the protective effects of the BCG vaccine are variable, decline with time, and offer no protection against the most common form of TB infection.
The hunt for a better TB vaccine is ongoing, and while there are perhaps a dozen different vaccines under development, human trials are expensive, time consuming, and difficult to mount ethically.
Today, The Lancet has published the fast-tracked results of a phase 2B trial (human safety and efficacy) of a booster vaccine called MVA85A, meant to be given to infants after they have already received the BCG vaccine in order to improve its protection.
This is literally the first new TB vaccine to undergo human trials in 90 years.
Unfortunately, while the experimental vaccine proved well-tolerated, it did not produce a significantly enhanced level of protection among the infants in the trial (1399 received MVA85A & 1398 received placebo).
In a 3 year follow-up there were 32 cases of TB among the children who received the MVA85A Booster, compared to 39 cases among those receiving the placebo.
The vaccine's efficacy rating of 17% was far below expectations.
In addition to the The Lancet study (below), you’ll find a comment (A major event for new tuberculosis vaccines) that states that these results “do not carry a terminal prognosis for MVA85A, or for any of the other TB vaccines under development”, along with an informative Podcast.
Safety and efficacy of MVA85A, a new tuberculosis vaccine, in infants previously vaccinated with BCG: a randomised, placebo-controlled phase 2b trial
Dr Michele D Tameris MBChB , Mark Hatherill FCP, Bernard S Landry MPH, Thomas J Scriba PhD , Margaret Ann Snowden MPH , Stephen Lockhart DM , Jacqueline E Shea PhD , J Bruce McClain MD , Prof Gregory D Hussey FFCH , Prof Willem A Hanekom FCP , Hassan Mahomed MMed , Prof Helen McShane FRCP , the MVA85A 020 Trial Study Team
Interpretation
MVA85A was well tolerated and induced modest cell-mediated immune responses. Reasons for the absence of MVA85A efficacy against tuberculosis or M tuberculosis infection in infants need exploration.
While the results announced today are disappointing, it is important to note that this study was conducted on infants. Unknown yet is how well this vaccine (or others in the works) might work as a booster for adolescents or adults with HIV.
For more background on the spread of TB, and efforts to combat it, you may wish to revisit these blogs.
EID Journal: Challenges To Defining TDR-TB
World TB Day Roundup
WHO: Blood Tests To Detect Active TB Unreliable
