What is the typhoid (Salmonella Typhi) vaccine?

From the Guidelines

Typhoid vaccine is recommended for travelers to areas where typhoid fever is common, particularly in parts of Asia, Africa, and Latin America, as an adjunct to hand hygiene and avoidance of high-risk foods and beverages, as stated in the 2017 Infectious Diseases Society of America clinical practice guidelines 1.

Key Points

• Two typhoid vaccines are licensed in the United States: an oral live attenuated vaccine (Ty21a/Vivotif) and an injectable Vi capsular polysaccharide vaccine (Typhim Vi) 1.
• The oral vaccine is approved for people 6 years and older, while the injectable vaccine can be given to those 2 years and older 1.
• The vaccines offer 50%–80% protection against typhoid fever, with the oral vaccine providing protection for about 5 years and the injectable vaccine for about 2-3 years 1.
• Booster doses are recommended for people who remain at risk, every 5 years for the oral vaccine and every 2 years for the injectable vaccine 1.

Recommendations

• Travelers to areas with moderate to high risk for exposure to Salmonella Typhi should receive typhoid vaccination, in addition to practicing good food and water hygiene 1.
• People with intimate exposure to a documented Salmonella Typhi chronic carrier, and microbiologists and other laboratory personnel routinely exposed to cultures of Salmonella Typhi, should also receive typhoid vaccination 1.
• The vaccine works by stimulating the immune system to produce antibodies against Salmonella Typhi bacteria, but it is not 100% effective, so practicing good food and water hygiene remains essential even after vaccination 1.

From the FDA Drug Label

DESCRIPTION Typhim Vi®, Typhoid Vi Polysaccharide Vaccine, produced by Sanofi Pasteur SA, for intramuscular use, is a sterile solution containing the cell surface Vi polysaccharide extracted from Salmonella enterica serovar Typhi, S typhi Ty2 strain. WARNINGS Allergic reactions have been reported rarely in the post-marketing experience (see ADVERSE REACTIONS section). The safety and immunogenicity of Typhim Vi vaccine in children under two years of age has not been established.

The Typhoid Vaccine (IM) is used to provide protection against the risk of infection related to Salmonella typhi.

• The vaccine contains 25 mcg of purified Vi polysaccharide in a colorless isotonic phosphate buffered saline.
• The vaccine does not protect against Salmonella paratyphi A or B, non-S typhi species of Salmonella enterica serovar Typhi, or other bacteria that cause enteric disease.
• The expected immune response may not be obtained in persons deficient in producing antibodies, such as those with asymptomatic or symptomatic HIV-infection, severe combined immunodeficiency, hypogammaglobulinemia, or agammaglobulinemia 2 2.

From the Research

Types of Typhoid Vaccines

• There are several types of typhoid vaccines, including the typhoid conjugate vaccine (TCV), live-attenuated oral vaccine Ty21a, and Vi capsular polysaccharide vaccine (Vi-CPS) 3.
• The live-attenuated oral vaccine Ty21a is based on the attenuated Salmonella typhi strain Ty21a and is the only attenuated live oral vaccine against typhoid fever 4.
• The Vi polysaccharide typhoid vaccine can be administered either intramuscularly or subcutaneously 5.

Mechanism of Action

• The Ty21a vaccine works by inducing specific immune responses, preventing infection and disease, and can be viewed as a 'magic shield' rather than a treatment for typhoid fever 4.
• The vaccine can also be used as a carrier for the delivery of heterologous antigens, allowing for efficient protein secretion from the carrier bacteria 4.

Effectiveness and Safety

• The Ty21a vaccine has been shown to elicit Salmonella Typhi-responsive CD4+ T cells in all major T memory subsets, including T effector/memory (TEM) and T central/memory (TCM) subsets 6.
• The vaccine has been found to be safe and immunogenic in preclinical trials, with no significant adverse effects reported 6.

Global Health Impact

• Typhoid fever remains a major global health problem, with an estimated 11 to 21 million cases occurring annually, and approximately 130,000-160,000 deaths 3.
• Vaccination against typhoid fever is an essential tool for the effective management of the disease, particularly in low- and middle-income countries where antibiotic resistance is a significant problem 7.