Indian Vi conjugate typhoid vaccine: misleading claims.

447 VOLUME 47__MAY 17, 2010 I refer to the article “Vi conjugate Typhoid Vaccine” written by Garg SP(1) on behalf of the manufacturer of Peda TyphTM in response to my previous article on the same subject(2). The author states that “this novel vaccine has been found to be safe and effective in inducing very high levels of immune response (>90%) in infants, young children and adults”, and goes further to claim that “this new vaccine can be used to vaccinate and protect patients after clinical recovery and thus prevent disease carriers and relapses”(1). Both these statements are misleading as for any typhoid vaccine, immuogenicity is not equal to efficacy, and serological correlates of protection for typhoid vaccines are not known. If the correlates were well established (as quoted by the author citing an old 1935 reference) why were the efficacy trials conducted for all the typhoid vaccines subsequently before they were marketed. Such field efficacy trials were also conducted for the experimental Vi conjugate vaccine (Vi-rEPA) by Dr. Robbins and are underway for other Vi conjugate vaccines in India. No such efficacy trial is available for Peda TyphTM anywhere in India or world. Claims that the vaccine will work in preventing carrier stage, and that it is expected to result in eradication of typhoid fever, are tall and misleading as no such data exists for any of the typhoid vaccine.