The Spanish flu of 1918 remains the worst flu pandemic on record, but there have been several milder ones since (see chart, below). A pandemic is a global epidemic and, in theory, flu does that every year in the northern and southern winters. But with flu, the term is reserved for when an influenza A virus emerges that isn’t just a slightly mutated version of last winter’s flu, but a complete novelty, with surface proteins most people have no immunity to.
Winter flu: All the essential facts you need to know
Novel viruses are constantly evolving in the birds, pigs and other animals that also carry influenza A, and they can shuffle their genes with human strains, or just adapt to mammals directly. Virologists consider flu pandemics inevitable. The World Bank says a bad one ““.
Like winter flu, the impact of pandemic flu depends on both the virus’s abilities and people’s immunity. The swine flu that went pandemic in 2009 was already adapted to causing only relatively mild illness in mammals. It still killed some 300,000 people. For once, older people were better protected: many people over 52 had immunity thanks to a related winter flu that circulated before 1957.
Advertisement
In 1918, many people over 71 were also protected, since a related winter virus seems to have circulated before 1847. But the Spanish flu was a bird flu that learned to transmit between mammals, and was equipped with fast gene-replicating enzymes that were adapted well to birds, but deadly in mammals. Young adults especially died in droves.
Our knowledge of the flu strains circulating in the past century means we are pretty sure almost no one will have encountered relatives of the next bird flu to go pandemic. Virologists sounded the alarm in 1997 when H5N1 bird flu jumped to people, but so far it has not acquired the mutations that would let it spread from human to human, a necessary condition for going pandemic. H7N9, which started infecting people in China in 2013, seems to have the required mutations already: a strain isolated recently spread readily, and lethally, , and was evolving resistance to Tamiflu, an antiviral drug crucial in saving severely ill people in 2009.
If a pandemic strikes, what could we do? The world’s single-strain vaccine production capacity has , with World Health Organization backing. But most producers grow vaccines in eggs, which takes months. In 2009, there was no vaccine before the first wave of swine flu was nearly over. Also, manufacturers have only the egg supplies for each hemisphere’s yearly production. There may not be enough eggs when everyone wants pandemic vaccine at once – especially if the emerging flu also kills chickens.
“A technological jump is required – either a universal flu vaccine or a rapid production platform”, such as insect cells or plants, says of the WHO. Facilities designed to combat pandemic flu will have to stay fighting fit by making other vaccines when there is no pandemic – not impossible, but commercially unprecedented. Both efforts could use a lot more funding. “The Manhattan project is an overused metaphor, but that is really what we need for flu vaccine,” says Osterholm.
Yet the world has flu fatigue. A decade ago, the emergence of H5N1 caused widespread panic. Now public investment has fallen, partly because the relatively mild 2009 pandemic wasn’t the disaster we feared.
The real problem, say epidemiologists, is that flu is so familiar. It can be mild – except when it isn’t. Until we recognise flu for the killer it is, we won’t do better at stopping it.
This article appeared in print under the headline “Winter flu: Everything you need to know – Is a big pandemic coming?”
