Complacency over the flu jab risks overwhelming the NHS, experts warn, as data reveals the scale of the challenge in expanding the vaccination programme.
Last month, the government announced plans to double the amount of people who receive the influenza jab.
But BBC analysis has found the take-up rate among those people in vulnerable groups eligible for a free jab has declined in recent years.
Academics say more needs to be done to explain the severity of the flu.
The government wants to increase the number of people vaccinated from 15 million to 30 million amid fears coronavirus cases will rise again in the autumn.
Local authorities in England saw an average 45% of people with serious health conditions under 65 take up the offer of