The introduction of the conjugated typhoid vaccine in India (Peda TyphTM),
and for the first time in the world, has come as one of the vaccines on
the wish list of pediatricians living in the South of Globe. 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.
Since this vaccine induces ‘T’ cell dependent response, it would get
boosted by field exposure and is expected to confer long lasting immunity.
This new vaccine can be used to vaccinate and protect patients after
clinical recovery and thus prevent disease carriers and relapses. We wish
to offer our views on the previous correspondence on this issue(1,2).
Serologic correlates of typhoid immunity induced by Vi
antigen was first reported by Felix and Pitt in 1935(3). Over the years
the protective immunity conferred by Vi antigen has been well established
and adopted by the WHO(4). The commonly known antigens of S. typhi
viz ‘O’ & ‘H’ antigens induce serological response which are not
protective in nature.
The valuable suggestion for bridging studies can only
be taken up when an equivalent vaccine becomes available(1). Clinical
trials are suggested involving more volunteers of all age groups over
longer periods to establish that results of Peda TyphTM
vaccine shall be similar to the Vi-rEPA vaccine in the Vietnam trials.
Bio-Med (P) Ltd shall support any such initiative to bring more scientific
information. Already more than 30000 doses of Peda TyphTM
have been used over past 6-7 months all over India in all age groups. If
doctors cooperate by providing serum samples for analysis, huge database
can be created.
Reservations have been expressed on the relevance of
vaccination for control of typhoid in India(2). Typhoid is very prevalent
in whole of India. Everyone knows about typhoid as a common disease which
has affected atleast one family member over 20 years time. The disease is
in the memory of everyone due to its characteristic fever lasting for over
3 weeks, damaging consequences and high cost of treatment.
Typhoid vaccine was withdrawn from the UIP of
Government of India in 1985 since the whole cell typhoid vaccine available
at that time was highly reactogenic and provided very low protective
value. The withdrawl of typhoid did not signal the significance of typhoid
in India. Epidemiologists in affected countries would like to see control
of typhoid by vaccination of over 60-70% population from the current
levels of 4-5% only. Vaccination is at least 10 times cheaper and will
save innumerable man days lost, doctor’s time, and hospital space, and the
pain and suffering etc.
The launch of Vi conjugated typhoid vaccine (Peda TyphTM)
is expected to bring an end of age old disease of man, since Salmonella
typhi has no other host except man as was the
case with smallpox virus.
Competing interests: Author is an employee of Bio-Med(P)
Ltd, which manufactures Peda Typh.
TM
References
1. Shah N. Indian conjugate typhoid vaccine: Do we have
enough evidence. Indian Pediatr 2009; 46: 181-182.
2. Mathew JL. Conjugate typhoid vaccine(s) in the
Indian context. Indian Pediatr 2009; 46: 182-184.
3. Felix A, Pitt RM. Virulance and immunogenic
activities of B. typhosus in relation to its antigenic
constituents. J Hyg 1935; 35: 428-436.
4. Requirements for Vi polysaccharide typhoid vaccine. WHO Technical
Report Series 1994; 840: 14-33.