The drop in the number of swine flu cases in England to an estimated 64,000 last week from 84,000 the previous week has been attributed to the half-term school break.
Sir Liam Donaldson, Chief Medical Officer, said it was difficult to give out any exact figures as officials believed the impact of half-term could last for two weeks.
He added next week's figures would provide a clearer picture of how the virus is developing.
The latest data showed there were 785 people in hospital suffering from swine flu, of which 173 were in intensive care - indicating a slight decrease. However, deaths due to the infection has increased, with 124 in England - up from 105 in the previous week.
A total of 182 people across the UK have died of swine flu, with 14 in Wales, 33 in Scotland and 11 in Northern Ireland.
In the meantime, the Department of Health is publishing new swine flu guidance for pregnant women, who fall under the high risk category.
Sir Liam said: "Our advice to pregnant women is if they are offered the vaccine, they should accept it."