To the Editor.—Dr. Shaw's points are well taken. We agree that the use of vaccine marker studies does not indisputably characterize a viral strain as being vaccine-derived. However, the results of our studies are highly suggestive that the virus recovered from the patient was originated from a vaccine strain. The methods we used for intratypic differentiation appeared highly reliable. As we pointed out, all the 167 strains of vaccine-derived type 2 poliovirus tested at the National Communicable Disease Center by both the Wecker technique and the temperature marker method had properties characteristic of vaccine virus. Likewise, all 102 wild type 2 strains tested by the Wecker method and all 157 strains of wild type 2 virus tested by the temperature marker technique were characteristic of wild virus.
We do not feel that this report should in any way be considered an indictment of oral poliovaccine. We all realize the