Sir, - Professor Tom Matthews's letter (September 13th) on Sudden Infant Death Syndrome (SIDS) was laudable in acknowledging that medical practitioners simply do not always know why this tragic event occurs. The professor gets no praise, however, for omitting any reference to the possibility of medically caused SIDS.It seems to me improbable that a high-profile paediatrician could be unaware of the studies supporting the association between vaccination and cot death (SIDS). For example, in "Confounding in Studies of Adverse Reactions to Vaccines", (J. M. Fine and L. C. Chen, American Journal of Epide- miology 136, 1992), research revealed that children died at a rate of eight times greater than average within three days of getting a DPT shot.Perhaps the medical establishment would prefer not to distress parents with this kind of alarming news. It seems to me, however, that it would be more appropriate for medical practitioners to share and discuss the conclusions of these kinds of studies with their patients, so that they understand the benefits and risks of the various medical procedures. How else can responsible parents make informed decisions on behalf of their children? -Yours, etc.,Myles Crowe,Seapoint,Co Dublin.