In Depth

The difference between coronavirus and flu

Influenza kills far more people, but experts say Sars-CoV-2 could ultimately prove more deadly if not contained

The new coronavirus outbreak has dominated the international news agenda in recent weeks, as more than 90,000 cases have been confirmed worldwide.

But another virus is currently causing far more illness and death around the world.

Influenza causes an estimated one billion illnesses and up to 650,000 related deaths each year, according to the World Health Organization.

Here are some of the differences between the two viruses.

The unknown

One of the key differences between flu and the new coronavirus, known as Sars-CoV-2, is how much is known about the two, and how experienced health professionals are in tackling them.

We know a lot more about influenza and what to expect compared with the coronavirus, and vaccines exist to protect at-risk groups from contracting flu.

“In contrast, very little is known about the new coronavirus and the disease it causes, dubbed Covid-19, because it’s so new,” says Live Science. “This means Covid-19 is something of a wild card in terms of how far it will spread and how many deaths it will cause.”

Dr Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told a White House press conference in January: “Despite the morbidity and mortality with influenza, there’s a certainty… of seasonal flu. I can tell you all, guaranteed, that as we get into March and April, the flu cases are going to go down. You could predict pretty accurately what the range of the mortality is and the hospitalisations [will be]. The issue now with [Covid-19] is that there’s a lot of unknowns.”

Symptoms

Flu viruses (there are three main strains) and Sars-CoV-2 are contagious viruses that cause respiratory illness. 

Typical flu symptoms include a sudden fever, an aching body, feeling tired or exhausted, a dry cough, a sore throat, headaches, difficulty sleeping, loss of appetite, diarrhoea or stomach pain, and feeling sick or being sick, says the NHS.

Symptoms of coronavirus include a cough, a temperature, and shortness of breath, says the health service.

Studies of patients hospitalised with coronavirus have found that about 83% to 98% of patients develop a fever, 76% to 82% develop a dry cough and 11% to 44% develop fatigue or muscle aches, according to a review study on Covid-19 published last week in the Journal of the American Medical Association.

Other flu-like symptoms, including headache, sore throat, abdominal pain and diarrhoea, have all been reported, but are less common, says Live Science.

Severity

Most people who get the flu recover in less than a fortnight, but the virus can cause complications in some people – especially children, the elderly, or those with existing medical conditions. These complications can lead to pneumonia.

Most cases of coronavirus are mild, with patients experiencing cold-like symptoms before recovering. Researchers from the Chinese Centre for Disease Control and Prevention in Beijing analysed 44,672 confirmed cases of coronavirus in China. Of those, 80.9% were considered mild, and only 13.8% cases were severe and 4.7% critical.

“Critical cases were those that exhibited respiratory failure, septic shock, and/or multiple organ dysfunction/failure,” the researchers wrote in the paper, published in CCDC Weekly.

Most of those critically ill from coronavirus are people more at risk from any viral disease.

“While we are still learning about how Covid-2019 affects people, older persons and persons with pre-existing medical conditions (such as high blood pressure, heart disease, or diabetes) appear to develop serious illness more often than others,” says the WHO.

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Fatality rate

Flu has a fatality rate – the percentage of known infected people who die – of about 0.1%, says The Times, much lower than that of the coronavirus.

One study of 1,099 laboratory-confirmed coronavirus patients in hospitals in China, published in the New England Journal of Medicine, put the death rate at 1.4%. It noted that the national official statistics suggested a higher rate, which is currently around 3.7% (2,945 deaths out of 80,152 cases reported in China).

Those in high-risk groups – older people and those with existing health conditions – could see around 15% of those infected with Covid-19 die, says Peter Openshaw, professor of experimental medicine at Imperial College London. However, says the Times, he noted that children rarely catch coronavirus, while flu can be dangerous for younger patients.

“It’s a new virus and we still are learning about how it behaves. We know a lot about flu – how to manage it and what it does,” Openshaw says. “We still don’t know exactly how it [Covid-19] spreads and what protective measures to take.”

Because a lot of mild cases might not be identified as Covid-19, the number of cases may be far higher, meaning fatality rates are lower.

“If borne out by further testing, this could mean that current estimates of a roughly 1% fatality rate are accurate,” says The Guardian. “This would make Covid-19 about 10 times more deadly than seasonal flu.”

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