Equipment failure caused the production of substandard vaccine by Wuhan Institute of Biological Products Co, the Hubei province Food and Drug Administration revealed on Friday. 

The vaccine packing equipment experienced a temporary fault that led to the uneven distribution of effective elements in the vaccine suspension, it said in a statement. 

Wuhan Institute of Biological Products, based in Hubei, produced a batch of 400,520 doses of substandard diphtheria, tetanus and whooping cough vaccine (DTaP) for infants. Another manufacturer, Changchun Changsheng Bio-tech Co in Jilin province, produced 252,600 substandard doses.

The 400,520 doses of substandard vaccine produced by Wuhan Institute of Biological Products were sold to Chongqing municipality and Hebei province, the administration said. 

The number of children vaccinated with them has not been revealed, but the administration said the remaining substandard doses had been recalled and destroyed by the manufacturer. 

It said health departments in Hebei and Chongqing had arranged since February for children given the substandard vaccine to be revaccinated. 

The 252,600 doses of vaccine produced by Changchun Changsheng Bio-tech Co were all sold in Shandong province, with 215,184 children being vaccinated, according to the Center for Disease Control and Prevention in Shandong. 

The China Center for Disease Control and Prevention said the substandard DTaP vaccines are not harmful to the human body, but could lead to poor immunity from the diseases targeted.