For certain high-risk groups, people over 65 years of age and those with underlying health conditions among them, a dose of flu can have serious ramifications. We talk to the head of flu at Public Health England about effective prevention and treatment.
Many people still perceive flu, the homely acronym for influenza, to be innocuous, an unpleasant inconvenience - one that is eminently avoidable by vaccine - rather than an existential threat.
Yet each year in advanced Western nations whose citizens have access to the best healthcare services, flu is responsible for thousands of deaths, particularly among high-risk groups.
How flu can kill
"For most people flu is generally mild, but in certain groups - people who are elderly and those with underlying health problems such as weakened immune systems, for example - it can be more serious, resulting in hospitalisation, and in extreme cases can be fatal," says Dr Richard Pebody, head of flu at Public Health England (PHE).
"Flu can cause serious conditions such as pneumonia and encephalitis, increasing the risk of secondary bacterial infections and also triggering problems with underlying clinical conditions such as heart and lung disease."
"The vaccine is the best defence we have against the spread of flu and for those who are eligible it isn't too late to get vaccinated."
Who is most at risk?
In addition to those aged 65 years, who tend to have weakened immune systems, and children and adults with a weakened immune system, pregnant women are also at increased risk from flu.
Pregnancy naturally weakens the body's natural defences, meaning the virus can cause serious complications for the woman and her newborn baby.
Children and adults with underlying health conditions that damage the immune system are also less able to fight off flu. According to PHE, those with chronic liver disease are approximately 48 times more likely to die if they develop flu than individuals who have no other underlying health condition.
Those with chronic renal disease are approximately 19 times more likely to die, patients with chronic heart disease 11 times more likely, and chronic respiratory disease sufferers seven times more likely.
Healthy children are also more susceptible to complications of flu - children under 5 years of age have the highest rates of hospital admission for flu, which can be reduced by up to 93% by introducing immunisation for all healthy children in an area.
Was the 2017/18 flu season exceptional?
Last year's flu season was the worst for seven years, with 15,000 deaths from the virus, around twice the average figure. Overall, an estimated 50,100 excess winter deaths occurred in England and Wales, the highest number in more than 40 years.
Three strains of flu circulated last winter: A(H3N2) - an infection that can especially impact older adults, resulting in more deaths, care home outbreaks and hospital admissions amongst older age groups, influenza B and A(H1N1)pdm09.
Pebody says there is evidence that virus A(H3N2) mutated during the manufacturing phase of the vaccine, meaning the resulting jab didn't give as good protection as hoped.
"In addition, the vaccine most adults received last winter only partially matched the flu B strain that was circulating," he adds.
The new vaccine
This year, PHE is offering adults below the age of 65 eligible for jabs - those with common health problems such as asthma and diabetes - a quadrivalent vaccine that protects against four key strains of flu (the previous version targeted three), while pensioners are being offered a boosted, or adjuvanted, jab.
"This year we recommend that all adults aged 18-64 receive the quadrivalent vaccine, and adults aged 65 and over will receive an adjuvanted flu vaccine," confirms Pebody. "The adjuvanted vaccine is intended to give a stronger and broader immune response."
The flu vaccine for healthy children, offered as a nasal spray rather than an injection, also protects against four strains of flu.
Prevention and treatment
GPs don't recommend antibiotics for flu since they don't relieve symptoms or speed up recovery, unless there is evidence of a secondary bacterial infection.
Antiviral medication may be prescribed to people in at-risk groups who present with a flu-like illness, in order to shorten the length of the illness, supported by a 2017 review of evidence by the European Centre for Disease Prevention and Control (ECDC).
"PHE recommends the use of oseltamivir (Tamiflu) or zanamivir (Relenza) to minimise the impact of flu on those in at-risk groups, who are at elevated risk of developing complications from flu infection," says Pebody.
"Antivirals are most effective when started as early as possible after influenza-like symptoms start - at least within the first 36-48 hours."
Simple hygiene can also help you avoid catching flu and prevent its spread. Carry tissues and use them to catch coughs or sneezes; bin the used tissues as soon as possible, and then wash your hands and kill the germs.
You can treat flu symptoms yourself by resting up, keeping warm, drinking plenty of water, and taking simple painkillers.
But - in the UK - contact your GP or NHS 111 if:
- Symptoms don't improve after seven days.
- You're worried about your child's symptoms.
- You're 65 or over.
- You're pregnant.
- You have a serious health condition - for example, diabetes or a heart, lung, kidney or neurological disease.
- You have a weakened immune system - for example, because of chemotherapy or HIV.