Saturday 17th January 2015
The health body says flu infection rates have topped those seen during the last three flu seasons, though they have not reached levels seen during the winters of 2010/11 and 2008/09.
The number of patients hospitalised due to flu remains low at 1.99 per 100,000, PHE said.
Doctors have warned that this year's flu vaccine may not protect against one mutated strain of the disease, and that this has contributed to some of the emergency hospital admissions.
Ben Marshall, a specialist in respiratory medicine at Southampton General Hospital, said: "We have seen the number of patients, mainly those who have respiratory conditions such as asthma or chronic obstructive pulmonary disease (COPD), being admitted as medical emergencies increase from 25 to 30 a day to more than 50 a day.
"Using a novel swab test, we have been able to rapidly discover what type of virus they are suffering from and a large proportion of them have had the influenza A H3 strain, which is now evading the immune response generated in recipients by the current seasonal vaccine."
A H3 is a severe strain that is included in the annual seasonal influenza vaccine but, this year, has mutated since the vaccine was prepared.
Dr Marshall said the majority of patients admitted with respiratory conditions complicated by illnesses such as flu and other viruses were being treated and discharged "within days" - but the volume was adding "significant strain" to already stretched hospitals.
PHE's head of seasonal flu surveillance Richard Pebody said this virus "drift" should not deter at-risk groups - including the elderly, pregnant women and people with chronic health conditions like asthma - from having the vaccine.
"Recently, only five of 24 UK virus isolates tested by the PHE Respiratory Viruses Unit show reduced antigenic reactivity to the current vaccine virus, showing a proportion of flu viruses circulating in the UK are likely to be drifted," he said.
"Further analysis will take place, but there is currently no evidence that the drift variant will become the dominant strain here, or that such a drift will result in reduced effectiveness of the 2014/15 vaccine.
"Existing vaccine is likely to still provide some protection and getting vaccinated remains the best way to protect yourself from flu."
The latest flu vaccine uptake figures from PHE show more than 70% of people aged 65 and over have been vaccinated.
But only half of those under the age of 65 who suffer from a health condition have had the jab, and among pregnant women the rate is only 43%.
Dr Tristan Clark, a specialist in infectious diseases and respiratory viruses at the same hospital, said high levels of influenza activity could continue until March.
He said: "The flu season began in the UK around four weeks ago, which is a bit earlier than last year, and admissions are up significantly.
"Based on the current trend and increasing hospital admissions, there is a high possibility we could continue to see such levels of activity for the next eight weeks."
Dr Clark, who is also a researcher in infectious diseases at the University of Southampton, explained flu preparations were made every year based on the flu season already seen in other parts of the world.
"We can sometimes predict what a flu season is going to be like based on the activity in the southern hemisphere before it reaches north of the equator and we know countries like Australia had a bad year," he said.
"Unfortunately, since the vaccine was prepared, the influenza A H3 strain has changed significantly, making the vaccine less effective at protecting against the virus - something we occasionally see."
Dr Penny Woods, chief executive of the British Lung Foundation, said: "It is still vital that people who are in the at-risk groups, such as those living with a lung condition, get vaccinated. Flu of any strain can leave people more susceptible to developing serious complications, such as bronchitis and pneumonia, and every year some cases of flu lead to hospitalisation and even death.
"It is therefore wise for those at greatest risk, do what they can to make sure that risk is minimised."