Two new TB vaccines show safety but limited protection

Two new vaccines to prevent tuberculosis (TB) are safe for use in adults and children, but they do not offer protection against all forms of TB, finds a large trial from India published by The BMJ today.

TB remains a major global public health concern. In 2023, an estimated 10.8 million people worldwide were reported to have TB and the rate of new cases increased by 4.6% between 2020 and 2020, highlighting the growing scale of the problem. BCG is currently the only licensed vaccine against TB. Yet although it is effective against severe forms of TB in young children, it does not offer protection for adolescents and adults. 

To address this gap, researchers in India conducted a large trial to evaluate whether two new TB vaccines (VPM1002 and Immuvac) can protect against all forms of tuberculosis (pulmonary and extrapulmonary), prevent latent (dormant) infection, and generate an immune response against the TB bacterium.

The study enrolled 12,717 household contacts (aged 6 years and older) of recently diagnosed TB patients across 18 sites in six Indian states between July 2019 and December 2020.

Participants were randomly allocated to receive a first dose of either VPM1002, Immuvac, or a placebo (4,239 in each group) and were followed up for 38 months. A second dose was administered to 11,829 participants one month later. A total of 12,295 participants (96.7% of those enrolled) completed 38 months of follow-up.

While neither vaccine offered general protection against TB or prevented latent TB infection, both demonstrated an ability to prevent the progression to active TB in those who developed latent TB.

The researchers found that although both vaccines did not show effectiveness against all TB and pulmonary TB (PTB), one of the vaccines, VPM1002 showed effectiveness (50.4%) against extrapulmonary TB (EPTB) across all age groups, including those aged 36-60 years (79.5%). These findings suggest a potentially significant public health benefit, because extrapulmonary TB, which affects organs beyond the lungs, is often associated with a higher risk of mortality than pulmonary TB. 

A promising key finding was the protection seen against TB in children, whereby VPM1002 provided protection against all TB, PTB and EPTB in the 6 to under 14 year age group, while Immuvac provided protection against EPTB only in the 6 to under 10 year age group.

However, neither vaccine protected children and adults who were underweight. This suggests that nutritional support may be needed along with vaccination, especially for younger children, report the authors.

Both vaccines were found to be safe and induced an immune response.

The researchers acknowledge that the covid-19 pandemic affected the study, leading to the exclusion of some participants who missed the second dose and sometimes delayed follow-ups. Furthermore, the findings may not apply in other countries or ethnicities.

Nevertheless, this was a large, well-designed study that reflects a real world scenario because it included both children and adults, regardless of pre-existing conditions like diabetes and risk factors, as reported by authors. Further research on commonly targeted high-risk groups for TB could be undertaken, they conclude.