Study Points to Added Benefits of Live Vaccines

A project by scientists at the University of Liverpool and Liverpool School of Tropical Medicine has shown that vaccination with weakened strains of Salmonella may also protect against other infections, which could impact vaccination strategy in the developing world.

Centred on Salmonella Typhi - the cause of the bacterial blood infection Typhoid fever which is estimated to affect between 11-18 million people worldwide - promising first data was obtained on the ‘non-specific’ immune response triggered by the live oral typhoid vaccine Ty21a.

“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,” said lead author Dr Shaun Pennington from the Liverpool School of Tropical Medicine.

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. The researchers vaccinated 16 healthy adults in the UK with the Ty21a vaccine and during six months looked at immune responses targeting Salmonella and a range of other pathogens. Changes to levels of infection-fighting white blood cells (monocytes) and immune system messengers (cytokines) in the group, suggested that Ty21a can strengthen the immune response against subsequent, unrelated infections.

“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,” said principle investigator Professor Melita Gordon from the University of Liverpool and Malawi-Liverpool-Wellcome Trust Clinical Research Programme.

The study received funding support from the Sir Jules Thorn Charitable Trust, the Rosetrees Trust, the Wellcome Trust and the Liverpool School of Tropical Medicine Director’s Catalyst Fund.

‘Nonspecific effects of oral vaccination with live-attenuated Salmonella Typhi strain Ty21a’ published in Scientific Advances [DOI: 10.1126/sciadv.aau6849]