A combined DTPa-IPV booster vaccine was administered as a 4th or 5th dose after DTPa or DTPw priming. Over 99% vaccines developed antibody levels considered to be protective to diphtheria, tetanus and poliovirus, and > 95% mounted a response to acellular pertussis antigens. Rectal temperature > 39.5 degrees C was observed in at most 3.2% of vaccinees. Swelling > 50 mm occurred in 24% of DTPa-primed compared to 5.5% of DTPw-primed children. Large swelling involving the entire upper arm (extending to involve the elbow joint) was reported for up to 1.2% of DTPa-primed subjects, which is consistent with literature reports for other DTPa vaccines. (c) 2005 Elsevier Ltd. All rights reserved.