Each dose of DPT vaccine contains 0.025 mg of mercury as thimersol and 1.25 mg of aluminium phosphate. Some preprations of hepatitis B vaccine, specially in multidose vials contain 0.025 mg of mercury as thimersol and 0.25 mg of aluminium hydroxide. There is still an ongoing debate whether mercury contained in the vaccine causes toxic effects on neurodevelopment of children and autism.

Cumulative doses of mercury and aluminium after three doses of DPT vaccine would be 0.075 mg and 4.5 mg of mercury and aluminium respectively. Adverse effect of mercury on the body depends on the load of mercury, period during which mercury has been administered, i.e., if mercury has been administered at short or long intervals and the body mass.

A different immunization schedule for three doses of DPT vaccine administered at 8, 16 and 24 weeks would pose least harm because the metals are administered over a longer period of time, as compared to the conventional schedule at 6, 10, and 14 weeks. Also, distribution of mercury/aluminium per kg body weight would be lesser, because the infant has a higher weight in the 8, 16 and 24 weeks schedule. Studies have shown that antibody generation is better when DPT vaccine is administered at 8, 16 and 24 weeks as compared to 6, 10 and 14 weeks.

Thus DPT vaccine administration at 8, 16 and 24 weeks should be considered. Similarly, if a mother is not a case of hepatitis B virus infection, administration of hepatits B vaccine to her child should be deferred to the latter part of infancy or even later.

Yash Paul,
A-D-7, Devi Marg,
Bani Park,
Jaipur 302 016, India.
E-mail: [email protected]