The largest outbreak of whooping cough for 20 years shows signs of slowing as cases fall for two months in a row, Health Protection Agency figures for England and Wales show.
There were 832 new cases in December, nearly half the figure from October.
One baby died in December, bringing the total number of deaths in newborns during the outbreak to 14.
Experts warn the outbreak may not be over as there is a seasonal dip in cases.
The current outbreak has been significantly worse than in previous years, affecting 9,741 in England and Wales in 2012.
There are surges every three to four years. However last year there were 10 times the number of cases than in the last outbreak in 2008. A similar pattern has been seen in Scotland and Northern Ireland.
Dr. Mary Ramsay, head of immunisation at the HPA, said: “The December figures show another welcome decrease in the overall number of whooping cough cases since the peak in October.
“However, it is very important to note that we usually see a reduction in cases of whooping cough at this time of year so this decrease is in line with normal seasonal patterns.”