The flu jab proved effective for just one in three adults who received it last winter, Public Health England (PHE) has said.
And the vaccine for children under the age of 18 offered a similar level of protection, at 35%, against strains of influenza A.
The success rate was better than first thought, with PHE warning at the time that the jab was only 3% effective, but it is still lower than typical past effectiveness of 50%.
Flu, along with cold weather, was said to have led to the number of deaths over the winter being up to a third higher than in previous years but officials said the vaccine remained "the best protection" against the virus.
Professor Paul Cosford, PHE's director for health protection and medical director, said: "In recent years, we have typically seen around 50% (ranging from 25 to 70%) effectiveness for the flu vaccine in the UK, and there has generally been a good match between the strains of flu in the vaccine and those that subsequently circulate. However, last year we saw a slightly lower vaccine effectiveness than usual.
"Whilst it's not possible to fully predict the strains that will circulate in any given season, flu vaccination remains the best protection we have against an unpredictable virus which can cause severe illness and deaths each year among at-risk group. These include older people, pregnant women and those with a health condition, even one that is well managed."
The study showed the child's jab had 100% effectiveness against influenza B, while the adult vaccines were 29.3% and 46.3% successful against A and B strains respectively.
PHE said in February the problem was caused by a "mismatch" between the A(H3N2) influenza strain used to make the vaccine and the main A(H3N2) strain that had been spreading around the UK.
But in its final report the body put the rise of efficacy of the jab down to "a shift in the dominant circulating strains" as the season continued.