Flu comes alongside each winter, however how many individuals it would infect – and simply how poorly they are going to be – is extremely tough to foretell. What makes one flu outbreak worse than one other?
After Australia skilled its worst flu season in additional than a decade, it was broadly anticipated that the arrival of winter would see extra individuals than traditional fall sick within the UK.
That is precisely what has occurred: this flu season is the worst for seven years.
The most recent figures show a 40% increase in the number of people going to GPs in England with suspected flu within the final week. Wales, Scotland and Northern Eire have additionally recorded will increase.
Issues will not be anticipated to enhance within the coming weeks – the UK has a nasty case.
Flu viruses are break up into three differing types: A, B and C Influenza, with a number of completely different strains inside these.
On this 12 months’s flu season, there are 4 strains circulating – and about half of hospital instances are attributable to the B pressure.
A is often probably the most deadly and is first transmitted from animals to people.
This winter one of many dominant strains circulating within the UK is a pressure of Influenza A referred to as H3N2, or Aussie flu.
The H3N2 pressure shouldn’t be new, however is a extra extreme pressure of flu than the H1N1 pressure that has circulated over the past two years.
It additionally differs from the strains lined by the present vaccine that has been given to many individuals.
Why flu is so unpredictable
Flu viruses are all the time competing to contaminate and cross between individuals – the virus strains most profitable at this are those that can grow to be dominant.
Predicting which of those strains will grow to be dominant in any given season is all the time a problem.
If, like this 12 months, the principle flu viruses are sufficiently completely different to earlier years and the strains within the flu jab, extra individuals could also be contaminated.
Flu viruses consistently evolve as they cross from individual to individual, altering their look so our immune system does not recognise them as simply.
As rule of thumb, if extra individuals obtain the flu vaccination, then fewer individuals will get flu.
The vaccine additionally reduces the severity of the signs – that means individuals are much less prone to go to hospital – and the danger of spreading it to different individuals.
Rising vaccine in eggs
Nonetheless, some flu vaccines are more practical than others.
They work by getting the immune system to recognise components of the influenza virus, so it responds extra successfully when it encounters the actual factor.
It takes eight or 9 months to develop and manufacture sufficient flu vaccine for one winter.
Flu jabs are nonetheless made in the identical approach they’ve been for greater than 60 years – by rising them in hen eggs.
This implies scientists should resolve which strains to incorporate in a vaccine many months earlier than the flu season really begins.
An enormous drawback is that the virus retains evolving earlier than the vaccine is prepared.
If the virus modifications greater than anticipated, or a minor pressure turns into unexpectedly widespread, the vaccine will probably be much less efficient.
Whereas this 12 months’s vaccine shouldn’t be as efficient as hoped, it’s nonetheless the perfect first defence obtainable.
A common flu vaccine that might defend towards all strains of flu remains to be a few years away.
Neither is it doable to guard everybody with the vaccine that’s obtainable.
To purchase sufficient doses, governments would want to provide vaccine corporations a few years’ discover, or construct new factories to provide sufficient.
There may be additionally the danger that the 12 months everybody was vaccinated is likely to be the 12 months when the strains of flu will not be significantly aggressive or simply unfold.
The vaccine might additionally embody the incorrect strains.
Crucially, no flu vaccine is 100% efficient and a small quantity of individuals would nonetheless get sick.
When a flu outbreak turns into a pandemic
Seasonal flu – as we’re at present experiencing – occurs yearly and often peaks within the UK in January and February.
Most individuals have some immunity to it, having had flu earlier than, or a vaccination.
These unfortunate sufficient to catch flu could really feel very sick, however will usually get well in a few week – though it may be lethal in a small variety of instances, significantly amongst younger youngsters and the aged.
Pandemic flu happens when a brand new virus pressure emerges from an animal.
Most individuals have little or no immunity as a result of they haven’t any earlier publicity to it, or related strains.
It impacts massive components of the inhabitants and spreads throughout many international locations.
Pandemic flu usually impacts youthful individuals greater than seasonal flu and there’s a a lot larger danger of great medical problems, hospitalisation and demise.
The final time the world suffered pandemic flu was the 2009 swine flu, which unfold swiftly the world over, infecting no less than 171 international locations and killing 457 people in the UK.
Fortunately this was not fairly as extreme a healthcare disaster as was first feared.
At instances, pandemic flu may be disastrous.
The Spanish Flu pandemic of 1918-19 introduced concerning the best variety of deaths from an infectious illness for the reason that Black Demise within the 14th Century.
It contaminated a 3rd of the planet’s inhabitants and killed an estimated 50 million individuals worldwide.
Most of the victims have been younger, in any other case wholesome adults and an infection usually led shortly to a lethal type of pneumonia.
On the time, no efficient medicine or vaccines existed to forestall or deal with it – a really completely different state of affairs to the one we at the moment are in, though we’re hardly effectively ready.
It is usually lucky that pandemic flu is uncommon – it emerged solely 3 times within the 20th Century.
The subsequent pandemic flu could not happen for 40 years, or it is likely to be subsequent 12 months.
It’s not possible to inform.
About this piece
This evaluation piece was commissioned by the BBC from an knowledgeable working for an out of doors organisation.
Prof Mike Turner is the pinnacle of An infection and Immunobiology on the Wellcome Trust, which describes itself as a world charitable basis working to enhance well being for everybody.
Edited by Duncan Walker