The observational studies' results of the DTP vaccine in Africa are noted to be biased and scored very low in the GRADE assessments.
Furthermore, among the ten observational studies, three suggested that simultaneous BCG and DTP administration may be preferable to the recommended schedule of BCG before DTP. There was a suggestion that mortality risk may be higher when DTP is given with, or after, the measles vaccine. Reportedly the methods followed during the studies are against WHO recommendation (Refer Page No.15). The six other studies with very high risks of bias produced highly variable results (Refer Page No.11). The majority of the evidence was generated by a group centered in Guinea-Bissau (Africa). There are negative effects in observational studies.
The WHO-commissioned studies have concluded that DTP's strong beneficial effects on overall mortality.