The flu vaccination program is estimated to have prevented about 104,000 hospital admissions last winter. Estimates of lives saved vary: one figure puts the death toll averted at over 7,100, while another accounting gives the number as 7,100 without the qualifier.

Vaccine effectiveness also appears to have slipped this year. One estimate holds that effectiveness in adults fell to 21 percent from 34 percent the year before; other data describes the range more broadly, putting adult effectiveness this year somewhere between 21 and 34 percent without specifying which figure belongs to which year. Effectiveness in children, who often spread the virus to others, was higher, measured at between 51 and 68 percent.

RSV poses a separate risk to older adults, causing an estimated 5,000 to 7,900 deaths a year in the UK among that group. The RSV vaccine was found to be 82 percent effective at preventing hospital admissions in adults aged 75 to 79.

Flu activity in September was higher than in any of the past four winter seasons, and hospital admissions that month also outpaced the same period in each of the previous four years, pointing to an early start to the season. Current flu case rates remain low, at 1.9 per 100,000 people. Flu levels peaked at the start of December last winter; this year's peak is expected to arrive earlier.

People with chronic lung conditions are seven times more likely to die from flu than those without them.

Health Minister Dame Diana Johnson is calling for increased vaccine uptake, as is Caroline Abrahams, director at Age UK. Dr Amanda Doyle of NHS England has urged eligible people to book their free flu vaccines immediately. Dr Jamie Lopez Bernal of the UKHSA said people over 65 and those with long-term health conditions face a higher risk of serious illness from both flu and RSV.