Paratyphoid fever primary prevention

Overview
Typhoid vaccine is recommended for travelers to areas where there is an increased risk of exposure to S.Typhi.

Indications for use
The typhoid vaccines do not protect against S. Paratyphi infection. Both typhoid vaccines protect 50%–80% of recipients; travelers should be reminded that typhoid immunization is not 100% effective, and typhoid fever could still occur. Two typhoid vaccines are available in the United States:


 * Oral live, attenuated vaccine.
 * Vi capsular polysaccharide (ViCPS) vaccine for intramuscular use.

Vaccine administration
The time required for primary vaccination differs for the 2 vaccines, as do the lower age limits.

Primary vaccination with oral Ty21a vaccine consists of 4 capsules, 1 taken every other day. The capsules should be kept refrigerated (not frozen), and all 4 doses must be taken to achieve maximum efficacy. Each capsule should be taken with cool liquid no warmer than 98.6°F (37°C), approximately 1 hour before a meal. This regimen should be completed 1 week before potential exposure. The vaccine manufacturer recommends that Ty21a not be administered to infants or children aged <6 years.

Primary vaccination with ViCPS consists of one 0.5-mL (25-mg) dose administered intramuscularly. One dose of this vaccine should be given ≥2 weeks before expected exposure. The manufacturer does not recommend the vaccine for infants and children aged <2 years.

Vaccine safety and adverse reactions
Adverse reactions to Ty21a vaccine are rare and mainly consist of abdominal discomfort, nausea, vomiting, and rash. ViCPS vaccine is most often associated with headache (16%–20%) and injection-site reactions (7%). No information is available on the safety of these vaccines in pregnancy; it is prudent on theoretical grounds to avoid vaccinating pregnant women. Live, attenuated Ty21a vaccine should not be given to immunocompromised travelers, including those infected with HIV. The intramuscular vaccine presents a theoretically safer alternative for this group.

The only contraindication to vaccination with ViCPS vaccine is a history of severe local or systemic reactions after a previous dose. Neither of the available vaccines should be given to people with an acute febrile illness.

Precautions and Contraindications
Theoretical concerns have been raised about the immunogenicity of live, attenuated Ty21a vaccine in people concurrently receiving antimicrobials (including antimalarial chemoprophylaxis), viral vaccines, or immune globulin. The growth of the live Ty21a strain is inhibited in vitro by various antibacterial agents, and vaccination with Ty21a should be delayed for >72 hours after the administration of any antibacterial agent. Available data do not suggest that simultaneous administration of oral polio or yellow fever vaccine decreases the immunogenicity of Ty21a. If typhoid vaccination is warranted, it should not be delayed because of administration of viral vaccines. Simultaneous administration of Ty21a and immune globulin does not appear to pose a problem.