Oral typhoid vaccination, which has weakened strains of a common bacteria, can also protect against other infections potentially saving lives in the developing world, the results of a clinical trial revealed.

Typhoid fever is a bacterial bloodstream infection caused by Salmonella Typhi that is estimated to affect between 11-18 million people and cause between 128,000-190,000 deaths annually worldwide. According to the US Centers for Disease Control and Prevention (CDC), there are two vaccines to prevent typhoid. One is an inactivated (killed) vaccine gotten as a shot. The other is a live, attenuated (weakened) vaccine which is taken orally (Ty21a).

The findings, published in the Science Advances journal, suggest that Ty21a can strengthen the immune response against subsequent, unrelated infections. "Live-attenuated Salmonella vaccines are low-cost, well-tolerated and easily administered," said lead author Shaun Pennington from the Liverpool School of Tropical Medicine in the UK.

"These vaccines could potentially be included in global vaccination programmes, not just for their impact on Salmonella, but also for their off-target, non-specific beneficial effects," Pennington added. Previous evidence has suggested that some live-attenuated vaccines, such as those for measles and polio, can stimulate the human immune system to generate a wider protective response and lower all-cause mortality.

In order to investigate whether Salmonella vaccines might offer similar protection, the researchers vaccinated a small group of 16 healthy adults in the UK with the Ty21a vaccine and studied its impact on their immune system over the course of six months.

The changes observed to levels of infection fighting white blood cells (monocytes) and immune system messengers (cytokines) suggest that Ty21a can strengthen the immune response against subsequent, unrelated infections. "Salmonella vector vaccines could provide Salmonella-specific protection, vectored-pathogen protection and non-specific protection, making live-attenuated Salmonella a hugely powerful 'triple threat' tool for global vaccine development," said Professor Melita Gordon from the University of Liverpool.