Q. I am a 39 years old man who had typhoid vaccine 9 months back. On the routine examination of blood, I was found reactive to salmonella. I have no fever or any other complaints. Can the vaccinne I took 9 months back be reactive to widal test and for how long?
Immunization with typhoid vaccines at regular intervals considerably reduces the incidence of typhoidal salmonella infections. Routine typhoid vaccination is indicated for persons with intimate exposure (e.g. household contact) to s. typhi cases or carriers, travellers to countries associated with an increased risk of exposure to s. typhi, and microbiology laboratory personnel working with s. typhi.
The following typhoid vaccines, killed and oral vaccines are used:
TAB vaccine: The TAB vaccine is a killed whole cell vaccine, which contains heat killed and 0.5% phenol preserved s. typhi, 1000 million and s. paratyphi A and B, 750 million each per ml. The vaccine has been used for many years in India and in other countries, endemic for enteric fever. The vaccine is given subcutaneously in 2 doses, of 0.5 ml each at an interval of 4 to 6 weeks, followed by a booster dose every 3 years. Field trials have shown overall efficacy of 70-90% in typhoid fever for a period of 3 years to 7 years. Fever and pain at site of the injection are the side effects. Injection of a large volume of antigen is also another concern. Therefore, in India, divalent typhoid-paratyphoid A vaccine without s. paratyphi B is used instead of the trivalent TAB vaccine, because s. paratyphi B infection is very rare in the country.
Vi capsular polysaccharide antigen vaccine (ViCPS): The Vi capsular polysaccharide (ViCPS) antigen vaccine is composed of purified Vi antigen, the capsular polysaccharide produced by s. typhi isolated from blood cultures. Primary vaccination with ViCPS is carried out by of a single parenteral dose of 0.5 mL (25 mcg IM). Booster doses are needed every 2 years to maintain protection if continued or renewed exposure to s. typhi is expected. The vaccine is not recommended for children below 2 years. Fever, headache, erythema, or induration are some of the side effects. Two field trials showed overall protection rates of 50-64% in South Africa and 72% in Nepal, the areas endemic for the disease.
Acetone-inactivated parenteral vaccine: This vaccine is currently available only in the USA only for military use. The vaccine has shown an efficacy of 75-94%. Booster doses are given every 3 years if continued or renewed exposure is expected.
Ty21a oral vaccine: This is an oral vaccine containing live attenuated s. typhi Ty21a strains in an enteric-coated capsule. S. typhi Ty21a strain is a stable mutant lacking the enzyme UDP-galactose-4-epimerase. On ingestion the strain initiates infection but after four or five cell divisions causes self-destruction, hence lacks the capability to cause any illness. Although the mechanism is unknown, the vaccine appears to stimulate both serum and intestinal antibodies and cell-mediated immune responses.
Primary vaccination with Ty21a consists of one enteric-coated capsule taken on alternate days to a total of 4 capsules. Booster doses are needed every 5 years to maintain protection if continued or renewed exposure is expected. It is essential to store the capsules in a refrigerator at 4ºC and to take all 4 doses to achieve maximum efficacy. Abdominal discomfort, nausea, vomiting, fever, headache, and rash or urticaria are rare but observed side effects following the vaccination. The vaccine is not recommended for immunocompromised persons, including those persons known to be infected with HIV and for children below 6 years.
Widal test is not a good test to measure post-vaccination antibodies but can cause confusion in interpretation as in your case.