Study Examines Non-Specific Protection of Typhoid Vaccine

Overview of Typhoid Fever

A recent study explored the potential protective effects of a typhoid vaccine against non-target microbes. Typhoid fever is an infection caused by the bacterium Salmonella Typhi (S. Typhi), affecting millions worldwide annually. The disease is transmitted through contaminated food and drinks, leading to severe complications such as gastrointestinal bleeding and a mortality rate of 10-20% if untreated. Antibiotic treatments can shorten the illness duration and lessen complications. Vaccination remains a crucial method for controlling typhoid fever, with Ty21a being a live attenuated vaccine that prevents S. Typhi infection.

Mechanism of Live Attenuated Vaccines

Live attenuated vaccines work by introducing a weakened form of the disease-causing germ into the body. This approach does not cause infection but stimulates a robust immune response, leading to long-term immunity against the relevant pathogens. Interestingly, vaccines may provide unexpected protection beyond their intended purposes.

Vaccines and Unrelated Mortality Reduction

Recent research has indicated that certain vaccines can reduce mortality rates in populations, an effect seemingly unrelated to the prevention of the specific diseases they target. This non-specific protective effect appears to be associated with live vaccines, including Bacille Calmette-Guerin (BCG), measles, and oral polio vaccines. The mechanisms behind this non-specific protection remain unclear, but scientists suggest that these vaccines may also prevent infections from other pathogens.

Investigating Ty21a Vaccine’s Non-Specific Protection

The Ty21a typhoid vaccine has shown similar non-specific protective properties. It has been associated with bladder cancer regression and enhanced immune responses against the influenza virus. A recent study published in the journal Science Advances examined the specific effects of the Ty21a vaccine on the human immune system.

Study Design and Methodology

Researchers recruited 30 volunteers aged 18 to 60 and divided them into two groups: one received the Ty21a vaccine while the other served as a control group. Blood samples were collected for cellular analysis at the time of vaccination, two weeks post-vaccination, and again at three and six months afterwards.

Immune Response Induced by Ty21a

Analysis of monocytes, a type of immune cell, revealed that their activation persisted for over three months in vaccinated individuals, whereas these cells typically circulate for only one day. This prolonged activation may correlate with the non-specific protection attributed to the typhoid vaccine.

In additional experiments, the immune response of white blood cells from vaccinated individuals was assessed upon exposure to various pathogens unrelated to typhoid fever. Results showed significant immune responses, notably against Candida albicans, Mycobacterium tuberculosis, and the influenza virus, through the production of specific cytokines, which are crucial for immune signaling.

Future Implications of Typhoid Vaccine Use

In conclusion, this study highlighted the non-specific protective effects of the Ty21a typhoid vaccine. Researchers monitored immune responses for up to six months in vaccinated individuals, discovering that the vaccine stimulates immune reactions against several non-target microbes. While further research is necessary to fully understand the immunity offered by this vaccine, the findings suggest its potential inclusion in future vaccination programs that leverage the non-specific immunity provided by Ty21a.

References

Pennington, S. H., Ferreira, D. M., Caamaño-Gutiérrez, E., Reiné, J., Hewitt, C., Hyder-Wright, A. D., Gordon, S. B., & Gordon, M. A. (2019). Nonspecific effects of oral vaccination with live-attenuated Salmonella Typhi strain Ty21a. Science Advances, 5(2).
Milligan, R., Paul, M., Richardson, M., & Neuberger, A. (2018). Vaccines for preventing typhoid fever. Cochrane Database of Systematic Reviews.
Goodridge, H. S., Ahmed, S. S., Curtis, N., Kollmann, T. R., Levy, O., Netea, M. G., Pollard, A. J., Van Crevel, R., & Wilson, C. B. (2016). Harnessing the beneficial heterologous effects of vaccination. Nature Reviews Immunology, 16(6), 392-400.
Typhoid vaccine may protect against other infections. https://www.eurekalert.org/pub_releases/2019-02/uol-tvm022519.php