Flu isn’t the underlying cause of death for more people than Covid-19

“Flu killing six times more people than coronavirus”

The Mirror, 19 August 2020

“FLU has killed more people in the UK than coronavirus for eight weeks in a row”

The Sun, 19 August 2020

“In the week to the end of July, five times more people died of influenza than Covid-19 in the UK.”

Dan Wootton, talkRADIO 13 August 2020

Several newspapers, magazines and broadcasters—including the Sun, the Mirror, the Mail, the Week, the Spectator, the Times and talkRADIO—as well as some social media accounts, have claimed that influenza (flu), or “influenza and pneumonia” is now causing more deaths than Covid-19 in the UK.

This is a misunderstanding of figures from the Office for National Statistics (ONS), which counts deaths in England and Wales. 

These figures show the number of deaths where influenza, pneumonia or Covid-19 are mentioned on the death certificate, not those where they were listed as the underlying cause of death. This makes it misleading to say that these are cases where people necessarily died “of” the disease, or were  “killed by” it, because in many cases influenza and pneumonia are only mentioned as factors in a death where the underlying cause was something else.

We don’t know exactly how many people are dying of flu at the moment—meaning that “flu” is the underlying cause—but it is almost certainly far fewer than these reports suggest.

With pneumonia included, the total number of people dying of pneumonia or flu is probably higher than the number dying of Covid-19 at the moment, but not by the margin that these headlines suggest.  

How deaths are categorised

Death certificates give doctors space to record several different diseases or conditions that contributed to someone’s death, but only one can be recorded as the underlying cause.  The underlying cause in this context means “the disease or injury which initiated the train of morbid events leading directly to death”. 

For example, someone might develop cancer, which leads to other conditions, from which they ultimately die. All of these conditions might be mentioned by a doctor on the person’s death certificate, but the cancer would be listed as the single underlying cause. It would be right to say that this person “died of” or “died from” cancer, and it would be misleading to say that they died of or from something else.

In its bulletin on the number of deaths being registered in England and Wales each week, the ONS reports the number of “deaths involving COVID-19”, which means the number of death certificates that mention Covid-19 somewhere, whether or not it was the underlying cause.

The ONS also reports in the bulletin the number of “deaths in England and Wales [that] mentioned ‘Influenza and Pneumonia’”. Again, they didn’t have to be the underlying cause of death. 

This matters, because when Covid-19 is mentioned on a death certificate, it is much more likely to be the underlying cause of someone’s death than when pneumonia or influenza is. 

Up to the end of June 2020 in England and Wales, Covid-19 was the underlying cause of death on about 93% of the death certificates that mentioned it. In 2015, 2016 and 2017, however, influenza or pneumonia were listed as the underlying cause of death on just 28% of the death certificates in England that mentioned either of them.

“Or”, or “and”, or “and/or”?

Another problem is that the reporting often summarised these deaths involving “influenza and pneumonia” as being deaths from “flu”, which is incorrect.  

The phrase “influenza and pneumonia” used by the ONS may have caused confusion here, because it sounds like it refers to death certificates that mention both, and so could be simplified to just “flu”. In fact, it refers to any mention that belongs in the “influenza and pneumonia” category.

This means that a death counted in the “Influenza and pneumonia” category could be someone who died after having pneumonia, or after having flu, or after having both.

Pneumonia is usually caused by a bacterial infection, but it can also be caused by a virus such as flu or the one that causes Covid-19. It’s worth noting that many people who die with Covid-19 have pneumonia as well, so the ONS explains that “deaths where both were mentioned have been counted only in the COVID-19 category”.

What does this mean for flu?

As we have seen, most of the people with influenza or pneumonia mentioned somewhere on their death certificate probably did not die with either as the underlying cause. And among those who did, the underlying cause was especially unlikely to be flu.

Flu is an important factor in many deaths. Estimates from the FluMOMO model suggest that there have been between 4,000 and 22,000 deaths associated with flu in England in each of the past winter flu seasons.

However, it is not often considered to be the underlying cause of death by doctors. 

If we look at the underlying cause of death data for 2019, we can see that 1,213 people died specifically from flu, which is just 4.6% of the 26,342 who died from either influenza or pneumonia.

In other words, on average, about 23 people died each week last year and had flu identified as the underlying cause of death (although this is likely an undercount and the disease may have been an important factor in many other deaths). 

Flu levels are unusually low right now, even for the summer. And the number of death certificates mentioning influenza or pneumonia is currently below the five-year average, as the ONS graph reveals. 

So what are the latest figures?

In the week ending 7 August, which is the latest reported by the ONS at the time of writing, 152 death certificates mentioned Covid-19.

If the proportion actually caused by Covid-19 is the same as it was in June (a more recent figure isn’t available), then about 93% of these deaths will have Covid-19 as their underlying cause, meaning about 141 of them. 

Over the same period there were 1,013 deaths registered with influenza or pneumonia, but not Covid-19, mentioned on the death certificate. If 28% of these had influenza or pneumonia as their underlying cause, which was the rate from 2015 to 2017, then this will make a total of 284 deaths from either cause. 

If we’re looking just at flu and 4.6% of those people who died had flu as the underlying cause identified on the death certificate, that would make just 13 people "killed by flu” in the same week. Though, as mentioned, this is likely an undercount.

These numbers are rough estimates. But they show that while pneumonia is probably killing more people than Covid-19 at the moment, there isn’t evidence that flu itself is killing more people than Covid-19.