How Typhoid Conjugate Vaccine is Transforming the Fight Against Typhoid

This photomicrograph reveals some of the histopathology exhibited in a lymph node tissue specimen, in a case of typhoid fever, caused by the bacterium, Salmonella typhi.
This photomicrograph reveals some of the histopathology exhibited in a lymph node tissue specimen, in a case of typhoid fever, caused by the bacterium, Salmonella typhi. Photo: CDC, 1964

In 2019, nearly 1.2 million people contracted typhoid in Pakistan, and 17,395 of those people died – 64% of who were children under the age of 15. Globally, about 20 million people get typhoid every year, yet we in higher income countries often do not hear about this disease and the millions of people affected by it. Typhoid, which is spread through contaminated food and water, has been eliminated in high-income countries because of investments in public health and sanitation systems. Many in low- and middle-income countries  lack these basic preventive mechanisms  to protect them from disease. The first sign of typhoid  may be a high fever, accompanied by fatigue, headache, abdominal pain, and diarrhea/constipation.

Typhoid is primarily found in Asia and sub-Saharan Africa, and children are disproportionately impacted in both the number of cases and deaths. According to an estimate from the Global Burden of Disease, 75% of typhoid-related deaths occur in Asia.

Scientists have been researching typhoid for over a century, but it is once again a growing concern due to a new threat: the emergence of drug-resistant strains. Drug resistant typhoid was first identified in the 1970s, but we are seeing more and more cases in recent years. In 2016, the first ever outbreak of Extensively Drug-Resistant (XDR) typhoid was discovered in Pakistan and over the next two years, more than 5,000 such cases were recorded with some strains responding to just one oral antibiotic, azithromycin.

Due to its substantial public health impact, scientists and medical professionals have worked for over a century to develop safe and effective ways to prevent and treat typhoid. Today, antibiotics are the only effective treatment for typhoid but growing drug-resistant strains have increased the demand for a vaccine – one that provides protection for all groups, including children, who have been impacted the most. An increase in cases of drug-resistant strains means that preventative measures such as a vaccine and improved water, sanitation, and hygiene are essential.

Vaccines for typhoid have existed for over a century, but they haven’t always been effective; however, the latest typhoid vaccine offers new hope. Typhoid conjugate vaccine (TCV) was recommended by the World Health Organization (WHO) in 2018 as the preferred vaccine due to its impressive safety and efficacy. Research shows TCV is more effective, provides longer-lasting protection, and is suitable for children younger than 2 years.

In November 2019, Pakistan became the first country to introduce TCV into their routine immunization system. Since then, Pakistan has vaccinated nearly 30 million children, and the benefits are undeniable: 66% reduction in typhoid cases following the introduction of the vaccine.

A research study published in 2021 investigated the effectiveness of TCV among 23,407 children in Pakistan. The study found that vaccine effectiveness was 55% against suspected typhoid, 95% against culture confirmed typhoid, and 97% against extremely drug-resistant typhoid. The findings of this study reflect the strong effectiveness of typhoid disease among the most impacted group in Pakistan.

Other high-burden countries are following Pakistan’s footsteps by introducing TCV to protect children and prevent typhoid. In late 2021, Liberia, Samoa, and Zimbabwe introduced TCV into their routine immunization systems. Nepal introduced TCV into its national routine immunization system in April 2022 and Malawi is planning to introduce TCV into their immunization schedule in late 2022. A TCV study conducted among Malawian children is already showing promising results with an 84% efficacy rate. TCV is a critical component in combating and eliminating typhoid in parts of the world that lack modern infrastructure and sanitation, but it is also an example of how a vaccine may be used to fight antimicrobial resistance. A recent modelling study indicated that incorporating TCV in routine immunizations could avert between 46% and 74% of typhoid cases and reduce the prevalence of drug-resistant typhoid by 16%.

Vaccinations can help reduce the likelihood of contracting the disease and reduce the fatality of the disease if contracted. For example, in Pakistan, the projected disease burden without implementing typhoid vaccination is an average of 421,000 cases and 635,000 deaths.

The data seems to show that expanding the coverage of TCV into routine immunization  reduces the need for antibiotics and slows down the emergence of drug-resistant typhoid. But most importantly, it will save lives, particularly of those most vulnerable: children. TCV can be a huge milestone in the battle to eliminate typhoid.

About the Author

Kayla Hunt was an intern with the Sabin Vaccine Institute during 2021 and 2022. She is a graduate student at Towson University studying Communications Management.