Coronavirus: An expert opinion on how COVID-19 compares to influenza

It's a claim you've likely seen on your Facebook feed sometime in the past week or two: that COVID-19 is no bigger threat to the world than influenza.

They might play the coronavirus down, saying most people just get a bit sick and recover, or they might point out influenza kills hundreds of thousands of people a year, but you don't see the media freaking out about that, or the World Health Organization (WHO) giving daily updates. 

Microbiologist Siouxsie Wiles says there's a good reason health authorities are taking COVID-19 seriously. Part of that is while influenza is a very well-understood disease, there's not a lot we know about COVID-19 - including how to stop it.

"Influenza is a virus that we do have vaccines for," Dr Wiles told Magic Talk. 

"The problem with [COVID-19 ] is it's not one that we've seen before, so we're not immune to it. We don't have any vaccine."

Siouxsie Wiles.
Siouxsie Wiles. Photo credit: Newshub.

COVID-19 emerged in Wuhan, China over the new year. By the end of January it had spread to more than a dozen other countries, and there are now more new cases reported each day outside of China than inside. 

So far there have been more than 3300 deaths and almost 100,000 infections officially confirmed, though there are fears this is an underestimate. 

According to WHO around 500,000 people die every year of influenza. Around 500 Kiwis are among that death toll, according to research by the University of Otago. 

But that obscures just how prevalent influenza is - around 10 percent of Kiwis catch the fast-evolving disease each year. 

 "The problem with influenza is it mutates every year - so we get different varieties, and every year we have to predict which are the variations that are going to come and make vaccines for those," said Dr Wiles.

"In a given year, most people have got some protection against influenza... Given how easily those viruses are transmitted and how often people transmit them... they actually have a pretty low death rate."

Influenza's mortality rate is about 0.1 percent. It's still early days for COVID-19, but estimates so far have ranged from 1 percent to 3.4 percent - and possibly more. 

"In the case of COVID-19 the time between onset of disease and death is quite long - two to three weeks or more - so the number of cases that you should divide by is not the number of cases that we have seen to this point, but the number of cases that there were a few weeks ago," Prof John Edmunds of the London School of Hygiene and Tropical Medicine said this week.

"In a rapidly expanding epidemic, that number will be much less, so the true case-fatality-ratio will be higher."

A 3.4 percent mortality rate would make COVID-19 a massive 34 times more fatal than influenza. 

Dr Wiles said even if its mortality rate was the same or lower than influenza "you would still see large numbers of deaths" because without any immunity or vaccines, everyone is at risk of catching it. 

"Also, quite a lot of people who get serious infections, even if they're not going to die, they require quite serious help in hospital. 

"What we don't want is overwhelming countries that do have good hospital systems, but also we don't want this virus getting to places that don't have the ability to care for people in hospital because they would see a far higher death rate than countries with good hospital systems. So I think there's reason to be concerned - this is quite different to influenza." 

COVID-19 also appears to have a higher R0 number than influenza - which means its easier to spread. For each person who contracts influenza, the average number of people they go on to infect is 1.3 - that's it's R0 number. COVID-19's R0 number appears to be about 2.2.

How to avoid catching COVID-19 on planes and trains

But there's a simple way to avoid catching it - washing your hands frequently and thoroughly. The virus can only enter the body through the eyes, nose or mouth, which is why you would likely have heard advice not to touch your face, if you can avoid it.

Just being on a train or plane with someone who's infected won't necessarily put you at risk, said Dr Wiles, which is why authorities are quarantining everyone who gets off a plane from Iran or China at the moment. 

"That's a lack of understanding of how this virus spreads. It's what we call a droplet-spread virus, rather than an aerosol or airborne virus. Droplet-spread means that when you cough or you sneeze you produce droplets and these fall onto surfaces, and then people can touch those surfaces and pick stuff up. 

"It's not that people are coughing and sneezing and all of this is going into the air circulation and that's spreading to everybody - that's not what happens in these cases. That's why there's no reason to be hauling everybody off the plane and putting them into isolation...

"We think if it's like other coronaviruses, they can survive on surfaces for quite a while - a few days - but at the end of things, you know, at the end of flights they're decontaminated. And provided you are washing your hands, you should minimise transmission."

How it doesn't spread

There were fears early in the outbreak that COVID-19 could be airborne like measles - which has an R0 value in the teens - but that appears now not to be the case. 

Also of relief is that people don't appear to be infectious prior to showing symptoms, which is why many people at risk of bringing the virus into the country are being put into self-isolation, rather than being rounded up and forced into quarantine. 

"There's very little evidence that anybody would actually be infectious during that period, so this is already a very cautious response. We are being cautious enough, definitely." 

Who to trust

Despite taking the threat seriously, Dr Wiles said no one should panic - not now, not in the future.

"It is serious in the grand scheme of things, but there's no reason to panic. I wouldn't even want us to panic if it was more serious here in New Zealand because when we panic, we don't often act in our best interests."

Rather than rely on "misinformation" spreading on social media, Dr Wiles said to trust the information and advice coming from health officials.

"What we all just need to do is when we see something, we just need to stop and ask, who is giving us this information, and why? And where did they get it from? If you're in any doubt at all, don't be sharing things on social media if they look dodgy."