Deaths caused by the flu may explain a drop in the average life expectancy across England and Wales last year.
New statistics reveal that mortalities reached a 12-year high between 2014 and 2015, which triggered a drop in life expectancy for both men and women.
In people aged 75 and over, flu was to blame for a significant number of deaths.
Claudia Wells, head of mortality analysis at the Office for National Statistics (ONS), who issued the findings, said: "The majority of the increase in deaths in 2015 happened during the first few months of the year."
She added that this coincided with an increase in hospital admissions for flu and reports of numerous outbreaks of the virus in care homes.
According to the ONS report, the increase in deaths resulted in the average life expectancy falling by 0.2 years for men - who are now expected to live to 79.3 years of age.
Meanwhile women's average life expectancy fell by 0.3 years to 82.9 years old.
Across England and Wales, there was a rise of 28,189 deaths in 2015 - from 501,424 deaths in 2014 to 529,613 in 2015.
This is the highest number since 2003, when there were 539,151 deaths, PA reports.
The vast majority of extra deaths in 2015 were registered in the first three months of the year.
The ONS report showed there were 24,201 extra deaths in those aged 75 and over in 2015 - accounting for 86% of the total increase.
There was also a rise in the number of people who died from underlying causes such as dementia or Alzheimer's disease.
This accounted for 41% of deaths among those aged 75 and over - although one third of these people also had respiratory disease, such as flu.
Dr Richard Pebody, head of flu surveillance for Public Health England, which helped conduct the research, explained that last year's flu vaccine was only 34% effective, which could have led to an increase in the number of deaths.
"A(H3N2) was the dominant subtype circulating last flu season in the UK," he said.
"In any flu season dominated by an H3 subtype, unfortunately we can expect the burden of illness to be seen in the elderly due to its intense nature.
"Winter 2014/15 was unusual because the circulating flu strain also drifted, making the vaccine 34% effective, lower than the typical 50% we had seen in recent previous years.
"It is possible that this exacerbated the situation further, leading to increased levels of excess mortality compared to recent seasons.
"The flu vaccine is updated every year and it is crucial that we remember that vaccination remains the best protection we have against the unpredictable flu virus."
Professor John Newton, chief knowledge officer at Public Health England, added: "A range of factors can push up the number of deaths in older people in a particular year.
"An outbreak of flu can have a big impact, especially on those who are most vulnerable or experiencing other illnesses, such as dementia."
Jeremy Hughes, chief executive of Alzheimer's Society, said the findings served as a "stark reminder" of the need to provide good community care to those with dementia.
He said: "People living with dementia often have a lowered immune system and so are at a greater risk of contracting flu viruses.
"The condition also makes it harder for people to look after themselves and in the cold winter months this can become a real danger."