Scientists are racing to create a flu vaccine that protects everyone
In 1962, the Nobel prizewinner McFarlane Burnet opened the latest edition of his book Natural History of Infection Disease with the kind of grandiose statement that, sooner or later, is bound to make even the most famed immunologist look a little naive. “At times one feels that to write about infectious disease is almost to write of something that has passed into history,” he wrote. At the time, Burnet had a point. Thanks to widespread vaccination regimes, smallpox – which by some estimates killed 300 million in the 20th century alone – was just 17 years away from total eradication. In the preceding 20 years vaccines for diphtheria, tetanus, polio and whooping cough had become routine in many countries, dramatically reducing the prevalence of deadly diseases that had once been widespread.
But for all of Burnet’s bravado, one infection has remained stubbornly difficult to get under control through vaccination. Flu. In the United States, last winter’s flu was particularly severe, leading to 80,000 deaths, the deadliest season since 1976, according to a preliminary figure from the Centers for Disease Control and Prevention.
When it comes to flu, vaccination is no guarantee of protection. Last winter in the UK, only 15 per cent of people who had the vaccine were protected against infection. In good years – such as the 2015/16 season – the percentage of people protected can be as high as 52 per cent, but often the figure hovers around 40 per cent or lower. But now scientists are racing to re-engineer the flu vaccine so it protects everybody, all the time.
At the moment, devising flu vaccines involves a surprising amount of luck. Twice a year the World Health Organisation meets to decide which flu strains will be protected against by that year’s vaccine. The resulting mixture – which usually protects against four strains – tends to read like a particularly exotic and unappetising cocktail.
This year’s flu vaccine, which was finalised way back in February to give pharmaceutical firms enough time to manufacturer and distribute it, is a good example. Each flu strain is named after the place it was first identified, and this year’s shot defends against strains from Michigan, Singapore, Colorado and Phuket, because these were identified as some of the most commonly circulating strains in the previous winter.
But a lot can happen between February and October – when the flu season in the northern hemisphere starts ramping up. Older flu strains that have been left out of this year’s vaccine might return, or as-yet-unidentified strains may rear their heads. Since each vaccine within the flu shot cocktail only protects against one flu strain, when either of these things happen the number of people protected by a vaccine starts plummeting.
Enter the universal flu vaccine. The hope is to create a vaccine that in one – or at a push, two – jabs that would give people immunity against all strains of flu. “The world needs a universal flu vaccine, because it just causes so many problems, so many deaths, especially in developing countries,” says Craig Thompson, who studies the evolution of infectious diseases at the University of Oxford.
Our current flu vaccines work by getting our immune systems to respond to a very specific protein embedded in the surface of each flu virus cell. Our immune system recognises these proteins – called epitopes – and produces antibodies to clear up the infection. Vaccines contain deactivated versions of the virus so your immune system memorises what those epitopes look like, and next time it encounters the virus for real, it can quickly produce those antibodies before you get ill.
The problem is that just one of these surface proteins comes in 18 different varieties – every one provoking a slightly different type of immune response. That’s why each vaccine has to be tailored to the particular flu varieties that the WHO hopes will be circulating that season. It’s just not possible to pack in resistance to every single possible strain in a single flu shot using our current way of creating vaccines.