Exposure to a fixed dose (e.g. 62.5 ug) of mercury at
2 months of age poses a greater potential risk than the same
dose administered at 6 months of age because a child weighs
more at 6 months and the target organ, the brain, is more
vulnerable early in life.
Similarly, exposures at 9-12 months would carry much
less theoretical risk than exposure to the same dose at 2
months of age.
The recent American Academy of Pediatrics/ Public
Health Service recommendation to defer the first dose of
hepatitis B vaccine for infants born to HBsAg negative
mothers until 2-6 months of age has addressed the problem of
exposure at birth, but the exposure to mercury at 2 months
of age is much greater and we need to do more to reduce this