TB Vaccine Timing Could Impact Effectiveness

06/23/2011 03:57 pm ET | Updated Aug 23, 2011

A new vaccine designed to fight tuberculosis is less effective when given alongside shots for other diseases, a study has found, suggesting child immunization programs in developing countries may need a rethink.

Data from clinical trials of the vaccine, called MVA85A, in babies in Gambia showed it was safe, but the immune response it prompted was lower in babies who got it with other infant immunizations than in those who got it on its own.

Martin Ota of the Medical Research Council Laboratories in Banjul, Gambia, who led the study, said the data should help doctors work out the best way to integrate the MVA85A into infant immunization programs in the future.

"We have a real opportunity to make sure that children are protected ... against tuberculosis by introducing effective and well-timed immunization programs," he said in a statement about the study. "This can only be achieved with robust information gathered from well-conducted clinical trials."

Standard childhood vaccinations are routinely given in developing countries as part of a plan known as the Expanded Program on Immunization (EPI).

It includes vaccines for diphtheria, tetanus and whooping cough, as well as the current vaccine for TB, Bacille Calmette-Guerin (BCG). The plan helps boost vaccine coverage by cutting the need for repeated visits to health clinics, which are often difficult to get to in poor, rural areas.

Although BCG protects against severe forms of TB in childhood, increasing rates of the disease in adults suggest its effect is not long-lasting.

TB is currently a worldwide pandemic that kills around 1.7 million people a year. The infection is caused by the bacterium Mycobacterium tuberculosis and destroys patients' lung tissue, causing them to cough up the bacteria, which then spread through the air and can be inhaled by others.

Experts say there is an urgent need for more effective TB vaccines and MVA85A -- being developed and trialed by Emergent BioSolutions in a joint venture with Britain's Oxford University -- is one of the most advanced potential candidates.

It has already been shown to be safe and capable of eliciting powerful immune responses in clinical trials in adults in Britain, Gambia and South Africa.

This study, published in the journal Science Translational Medicine on Wednesday, was the first trial to evaluate the safety of the vaccine in babies. It involved 214 healthy four-month-old infants who had already received BCG at birth.

The children were given either EPI alone, MVA85A alone, or MVA85A with EPI, and their immune responses were monitored.

Overall, Ota's team reported, MVA85A was deemed to be safe, well tolerated and induced a strong immune response. And importantly, the responses to the standard EPI vaccines were not affected by giving MVA85A at the same time. But the immune response prompted by MVA85A was lower in infants who received it with EPI vaccines, compared with those who got it alone.

"It's reassuring to see that MVA85A does not affect immunity to the other vaccines," said Helen McShane of Oxford University, who helped develop the new shot. But she said scientists would now need to find the best way to integrate MVA85A into infant immunization plans in future without limiting its effect.

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