The typhoid vaccine may protect against other infections and save hundreds of thousands of lives.
Researchers have found that by vaccinating people with weakened strains of Salmonella their immune systems were strengthened against other viruses and diseases, not just typhoid.
Typhoid fever is a bacterial bloodstream infection caused by Salmonella Typhi – it is estimated to affect between 11 and 18 million people and causes between 128,000-190,000 deaths worldwide every year.
The findings, by researchers at the University of Liverpool and Liverpool School of Tropical Medicine, could save hundreds of thousands of lives in the developing world where infectious diseases are common.
The study, published in the journal Science Advances, showed promising initial results on the ‘non-specific’ immune response triggered by the live oral typhoid vaccine Ty21a.
The vaccine is ‘live-attenuated’, meaning it works by reducing the infectious element of the disease or virus, rendering it almost harmless.
When administered it triggers an immune system response which protects against Typhoid and, as the results indicated, other infections.
Lead author Dr Shaun Pennington, of the Liverpool School of Tropical Medicine, said: “Live-attenuated Salmonella vaccines are low-cost, well-tolerated and easily administered.
“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.”
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.
To investigate whether Salmonella vaccines might offer similar protection, the researchers vaccinated a 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.
They looked at immune responses targeting Salmonella as well as those targeting a range of other pathogens – viruses or bacteria that cause disease.
The changes they observed to levels of infection-fighting white blood cells (monocytes) and immune system messengers (cytokines) suggested that Ty21a can strengthen the immune response against subsequent, unrelated infections.
Principal investigator Professor Melita Gordon, from the University of Liverpool and Malawi-Liverpool-Wellcome Trust Clinical Research Programme, said: “The next step is to observe whether these responses also occur in children in low-income settings where their impact would be greatest.
“We’d like to conduct further clinical studies, where we will be able to assess the wider impact of our observations in conferring protection against other common infections, not just Salmonella.”
The researchers said that the ability to manipulate live-attenuated Salmonella so that they express components of other pathogens could make their findings particularly exciting for future ‘vector vaccine’ design.
A vector vaccine uses a chemically weakened virus to stimulate an immune response in the receiver.
Professor Gordon added: “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.”