We will all be exposed to flu this winter, but not all of us will get sick. The best way to minimise the risk is clear – although it’s a far from perfect solution.
What makes flu lethal?
Flu’s familiarity belies its deadliness. This year marks the centenary of the deadliest pandemic of recent years, the Spanish flu of 1918 that killed up to 100 million, some 5 per cent of humanity at the time.
The way flu kills directly is mostly by causing viral pneumonia, a deep infection that damages the lungs’ oxygen-absorbing membranes. Pneumonia can also happen indirectly if the flu virus wipes out immune cells that normally keep bacteria in your lungs at bay, triggering a bacterial infection. Compromised immune systems, for example in elderly people and pregnant women, allow the virus to replicate more freely and make flu more dangerous.
Winter flu: All the essential facts you need to know
Especially in elderly people flu can also cause excessive levels of inflammation, normally a broad immune defence against germs. Each year, right after flu season, there is a second, broadly equal wave of deaths from inflammation-triggered conditions such as heart attack and stroke. Chronic conditions that boost inflammation such as obesity can make flu more dangerous.
Pneumonia linked to flu is the fourth biggest killer of women in the UK, and the sixth biggest killer of men (see diagram). According to the first worldwide direct estimate, published by the World Health Organization (WHO) in December 2017, the yearly toll is up to 650,000 just from lung disease, and 1.3 million from all causes – twice what we thought. “If we had another vaccine-preventable virus killing that many people we’d be outraged,” says Bram Palache of FluPal Consultancy in Amsterdam.