Using the Australian Childhood Immunisation Register to track the transition from whole-cell to acellular pertussis vaccines.

From 1997 to 1999, Australia changed from a whole-cell based pertussis vaccination program to an acellular one. This paper tracks the transition from whole-cell to acellular pertussis vaccines by calculating the number of whole cell (DTPw) and acellular (DTPa) pertussis vaccines recorded on the Australian Childhood Immunisation Register (ACIR) each month from January 1996 to August 2000. The number of combined diphtheria-tetanus (CDT) vaccines, recommended where DTP is contraindicated and for the fifth dose prior to 1994, was also calculated. The use of DTPa increased following its licensing in 1997, with a corresponding decrease in the use of DTPw. The increase was initially greatest in its use as a fourth and fifth dose, for which it was funded at a national level in 1997. Subsequently, a steep increase in its use for the first three doses followed in 1999, coinciding with it becoming free of charge for infants nationally. The use of CDT has decreased markedly since January 1996 and, since March 2000, fewer than 100 CDT vaccines per month were recorded on the ACIR, suggesting that this vaccine is not being inappropriately used.