The World Health Organization (WHO) has identified typhoid as a major global health concern, with an estimated 9 million people falling ill and 110,000 dying from Salmonella Typhi, commonly known as typhoid, each year. In 2024, children in typhoid-endemic countries, especially in Asia and sub-Saharan Africa, face significant risks due to inadequate access to safe drinking water and proper sanitation.
The WHO warns that travelers to these regions are also at risk due to low food hygiene standards and poor water quality. However, there is good news on the horizon – approved typhoid vaccines are available, offering hope for prevention and control.
The effectiveness of these vaccines, particularly their duration of protection, has been a topic of debate. Thankfully, a recent peer-reviewed study conducted by researchers at the University of Maryland School of Medicine (UMSOM) has shed light on this issue.
Published in The Lancet on January 25, 2024, the study focused on a phase 3 clinical trial of the Vi polysaccharide conjugated to tetanus toxoid vaccine (Vi-TT). It discovered that a single dose of this vaccine provides durable efficacy for at least four years in children and is effective across all age groups, including children under two years old.
The study’s findings have significant implications, as they support the long-lasting impact of a single dose of the Vi-TT vaccine, even in the most vulnerable children. Dr. Kathleen Neuzil, CVD Director and coauthor of the study, remarked that these results offer hope for preventing typhoid in children who are at the highest risk.
During the trial, 28,130 children received the Vi-TT vaccine, and after a median follow-up of 4.3 years, the incidence of typhoid fever was significantly reduced. The efficacy of the vaccine was found to be 78.3%, indicating that only 163 children needed to be vaccinated to prevent one case of typhoid.
These promising results align with the current recommendations of the WHO for mass vaccination campaigns among children aged nine months to 15 years in typhoid-endemic regions. Subsequently, routine introduction of the vaccine in the first two years of life should be implemented.
The development of typhoid vaccines has been a progressive journey, beginning with whole cell inactivated versions in the 19th century, which had adverse side effects. Second-generation vaccines, such as live attenuated vaccines and capsular polysaccharide vaccines, faced limitations in terms of age restrictions and lower immunogenicity in young children.
To overcome these challenges, typhoid conjugate vaccines (TCVs) were developed, which have demonstrated robust immune responses. Currently, TCVs, including the prequalified Typbar TCV® developed by Bharat Biotech, are available and have shown high immunogenicity and efficacy in preventing typhoid infections.
While typhoid cases are relatively rare in the United States, mainly occurring in individuals who have traveled internationally, the Centers for Disease Control and Prevention (CDC) offers two typhoid vaccines for those at risk. These include an inactivated (killed) vaccine and a live, attenuated (weakened) vaccine. Healthcare providers can assist individuals in determining the most suitable vaccine for their needs.
It is important to note that no vaccine currently protects against paratyphoid fever, another strain of the Salmonella bacterium. This highlights the need for continued research and development in the field of typhoid prevention.
Through the support of organizations like the Bill & Melinda Gates Foundation, the Typhoid Vaccine Acceleration Consortium is driving advancements in typhoid vaccine development and implementation. Their efforts aim to protect vulnerable populations and reduce the global burden of typhoid fever.
Frequently Asked Questions (FAQs) about Typhoid Vaccines
1. What is typhoid and why is it a global health concern?
Typhoid, caused by Salmonella Typhi bacteria, is a serious infectious disease that affects millions of people worldwide each year. It poses a major global health concern due to the high number of illnesses (9 million) and deaths (110,000) it causes annually.
2. Who is at risk of typhoid infection?
Children in typhoid-endemic countries in Asia and sub-Saharan Africa are particularly at risk due to inadequate access to safe drinking water and proper sanitation. However, travelers to these regions are also vulnerable to typhoid due to low food hygiene standards and poor water quality.
3. Are there vaccines available for typhoid prevention?
Yes, there are approved typhoid vaccines that offer hope for prevention and control. One such vaccine is the Vi polysaccharide conjugated to tetanus toxoid vaccine (Vi-TT).
4. What does the recent study conducted by the University of Maryland School of Medicine reveal about the Vi-TT vaccine?
The study found that a single dose of the Vi-TT vaccine provides durable efficacy for at least four years in children and is effective across all age groups, including children under two years old. These findings suggest that even the most vulnerable children can benefit from a single dose of this vaccine.
5. What is the efficacy of the Vi-TT vaccine?
The study discovered that the Vi-TT vaccine has an efficacy of 78.3%. This means that vaccinating 163 children would prevent one case of typhoid.
6. What are the current recommendations by the World Health Organization (WHO) regarding typhoid vaccination?
The WHO recommends mass vaccination campaigns among children aged nine months to 15 years in typhoid-endemic regions. Additionally, routine introduction of the vaccine in the first two years of life is advised.
7. Are there other typhoid vaccines available besides the Vi-TT vaccine?
Yes, there are typhoid conjugate vaccines (TCVs) available, such as the Typbar TCV® developed by Bharat Biotech. These vaccines have shown high immunogenicity and efficacy in preventing typhoid infections.
8. What typhoid vaccines are available in the United States?
In the United States, the Centers for Disease Control and Prevention (CDC) offer two typhoid vaccines: an inactivated (killed) vaccine and a live, attenuated (weakened) vaccine. Healthcare providers can help determine the most appropriate vaccine for individuals at risk.
9. Does any current vaccine protect against paratyphoid fever?
No, currently there is no vaccine available that protects against paratyphoid fever, a strain of the Salmonella bacterium. Continued research and development efforts are needed in this area.
– Typhoid: A serious bacterial infection caused by Salmonella Typhi.
– Typhoid conjugate vaccine (TCV): A vaccine that protects against typhoid infections by stimulating immune responses.
– Efficacy: The effectiveness of a vaccine or treatment in preventing or reducing disease incidence.
– Endemic: Refers to the constant presence of a disease within a specific geographic area.
– Immunogenicity: The ability of a substance to provoke an immune response.