Q. What are the side effects of typhoid vaccines?
Whole cell killed typhoid vaccine :- This vaccine fell into disrepute due to high incidence of local & systemic effects especially with availability of safer alternatives like the Vi antigen & the oral ty21a vaccines. The local side effects including pain, swelling, redness, pain on walking, tenderness etc. are seen in 50% of vaccinees. It lasts for 2-5 days & responds to paracetamol. The systemic side effects include high-grade fever, chills, headache, vomiting, and bodyache, which are seen in 30-50 % of vaccinees. It lasts for 2-3 days & responds to paracetamol

Vi antigen vaccine :- It can lead to local side effect like pain, swelling, redness, tenderness etc. The side effects are very mild and are seen in < 10% of vaccinees, last for 24 hours & respond to paracetamol. Systemic side effects are rarely seen & include mild fever lasting for 24 hours, which responds well to paracetamol.

Oral ty21a vaccine :- It leads to mild GI discomfort like pain in abdomen, vomiting, diarrhea & occasionally mild fever. Again, the reactions are less common, mild and self-limiting. The Vi antigen vaccine and the oral ty21a vaccines are very safe and least reactogenic. Hence they are preferred over whole cell killed vaccine.

Q. How does one treat side effects of typhoid vaccine?
One can use paracetamol or ibuprofen to treat local side effects or fever following vaccine. As whole cell killed vaccine has higher incidence of the side effects one can use paracetamol in every patient prophylactically.

Q. Which of the three vaccines is preferred?
Comparison between the 3 vaccines is done in table I.

Whole cell killed vaccine is cheaper & can be given as early as 6 months of age. But it needs 2 injections & can lead to frequent unpleasant side effects. Phenol killed vaccine which was available in open market was less efficacious than other typhoid vaccines. Being cheaper it can used for mass vaccination. Unfortunately it is not available currently.

Vi antigen vaccine is a single use, sure shot vaccine and does not involve compliance. It is efficacious & safe & has infrequent & mild side effects. It can be started only after 2 years of age. It is costlier than whole killed vaccine but cheaper than the oral vaccine.

Oral ty21a vaccine being an oral vaccine is easily accepted. It is efficacious & safe with infrequent & mild side effects. Being oral, it is ideally suited for mass vaccination. However it is the costliest of all the three. It can be given only after 4-6 years of age, as the capsules need to be swallowed intact. One has to avoid antibiotics active against S. typhi for 5 days before, during & after vaccination as being a live vaccine, it would be inactivated by the antibiotics. One needs to take 3 capsules to complete the course, hence compliance is important. In case a capsule is opened or chewed, one needs to buy one more pack of 3 capsules adding to the cost. Being live vaccine, strict cold chain maintenance is required &I t is also contraindicated in immunocompromised child.

Table I: Comparison of 3 types of typhoid vaccine