Evaluation of the potential of new and repurposed TB vaccines

By Dr. Priyom Bose, Ph.D.Reviewed by Aimee MolineuxMay 5 2022

Scientists reported that tuberculosis (TB) is one the foremost causes of global mortality, especially in adults. In 2019, around 10 million TB cases were reported, many of which were identified to be resistant to multiple drugs.

To date, only one TB vaccine is available, namely, the Bacillus Calmette Guérin (BCG), which is recommended for newborns only.

Although this vaccine can effectively prevent TB meningitis and disseminated TB in young children, it can only partially protect against pulmonary TB. Hence, there is a need to develop more effective TB vaccines to realize the World Health Organization’s goal of ‘End TB’.

Background

Researchers predicted that the development of TB vaccines for adolescents and adults could have a greater and faster effect on eradicating TB. There is a gap in research regarding the assessment of the length of protection provided to young adults immunized with the TB vaccine. In the case of vaccinated infants, the effectiveness of the TB vaccine was found to last for up to 15 years and sometimes even longer. 

Currently, policymakers are debating the reintroduction of BCG revaccination in young adults to decrease the global mortality rate associated with TB. However, not enough evidence is available on the potential strategy for an effective TB vaccination program for adolescents and adults.

The study

A new study published in PLOS Global Public Health has focused on evaluating the effective vaccination strategies for two TB vaccines, i.e., M72/AS01E and BCG. The authors also assessed the possible advantages as well as challenges associated with new vaccination programs.

In this study, researchers conducted interviews, between May and December 2020, with policymakers as well as immunization stakeholders in three countries, i.e., South Africa, India, and China. They selected these countries because of the high prevalence of TB. The interviews were structured in two sections, i.e., a) determining the acceptability and feasibility of vaccinating adolescents and adults with TB vaccines and b) assessment of probable implementation scenarios.

Scientists assessed the acceptability and feasibility of vaccinating adolescents and adults with the TB vaccine from interviews with experts from the above-stated countries. The authors also determined country-specific settings that would ensure successful TB vaccination programs. 

Key findings

All three countries have been interested in vaccinating adolescents and adults with the TB vaccine, especially, school-aged children as they are more vulnerable to contracting the disease. Scientists observed that each country proposed different implementation strategies, owing to their varied demographic and epidemiological settings.

In China and India, older aged individuals were prioritized for vaccination. However, all the countries favored routine vaccination programs to overcome logistical challenges. Experts expressed the urgent need for TB control strategies and novel vaccines to protect all individuals from the disease. Interviewees reported that the implementation of TB vaccination would help reduce the massive TB burden that has been observed in all countries.  

The predicted effectiveness of the M72/AS01E vaccine in patients infected with Mycobacterium tuberculosis (Mtb) and HIV highlighted the benefits of TB revaccination. Two of the challenges associated with the implementation of M72/AS01E are the development of new infrastructures and the two-dose vaccination regime.

Additionally, for mass vaccination of M72/AS01E, interviewees predicted a lower coverage for the second dose of the vaccine. The experts also stated that pre-vaccination testing would be essential to identify Mtb positives or negatives, which could be expensive and infeasible. 

Interviewees suggested conducting clinical trials in local settings to obtain TB epidemiological data and spreading the knowledge about the benefits of TB vaccines could help reduce vaccine hesitancy. These measures would help support the implementation of the vaccination. In both India and South Africa, school-based Human papillomavirus (HPV) vaccination program is practiced, and in the current context, as the target group of TB vaccination is also school-aged children, implementation of this vaccination strategy could be beneficial.

In both India and South Africa, socially vulnerable groups have been prioritized for M72/AS01E, owing to a high rate of incidence of TB among these groups. The experts expressed the need for suitable monitoring systems and proper education on TB disease and vaccination in communities. 

The current study reported that the affordability of the vaccine plays an important role in its uptake and distribution. All the interviewees emphasized proper information about the efficacy, safety data, and cost-effectiveness of the vaccine.

Limitations

One of the limitations of this study is the exclusion of the patient population to analyze the acceptability and hesitancy of the vaccine. In this study, scientists only considered the views of policymakers and other direct stakeholders, such as vaccination program implementers.

Another limitation of this study is that as BCG was discussed second to M72/AS01E during the interview, not much time was devoted to its discussion. Additionally, an underrepresentation of interviewees from civil society, finance, local level, etc., was observed.