FACTS OF PAINLESS VACCINE

There is no painless vaccine. The only vaccine that is subject to this confusion is DTP v/s DTaP. As compared to DTP DTaP has a lower incidence of fever as it has acellular Pertussis.

The issue of having low fever with DTaP is extending to less crying & this is reversely attributed to less pain, hence the "painless vaccine concept" leading to less effective in the future against the virus. 

Even the Academy of Pediatrics recommends a painful vaccine, pain is a matter of 2 days but immunes for a lifetime.