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There are lots of things we don’t know about coronavirus. We don’t know why men are more likely to die from Covid-19, for example, or why some people contract the virus without showing any symptoms.

Amongst all this uncertainty, the daily UK death tolls issued by the Department of Health and Social Care (DHSC) may seem incontrovertible, but even here we are somewhat in the dark. On April 1, for instance, the DHSC reported that 2,352 people had died so far after contracting Covid-19. But just over two weeks later, the Office for National Statistics (ONS) released data showing that in the whole of March, 3,912 people had died from Covid-19.


But why are the figures so different? Unlike the daily counts published by the DHSC and recited at the government’s daily press briefings, the ONS figures include people who died outside hospital, that is in care homes, hospices and their own homes. Of the deaths involving Covid-19 and registered by April 3, 217 occurred in care homes, 33 in hospices and 136 in private homes (adding up to ten per cent). The figures also include suspected deaths, not just people that tested positive for the virus. However, it takes at least five days between a doctor certifying a death and it being registered so it may take weeks until the true scale of deaths becomes apparent.

As Sarah Caul, head of mortality at the ONS, wrote in a blog post: “Numbers produced by ONS are much slower to prepare, because they have to be certified by a doctor, registered and processed. But once ready, they are the most accurate and complete information.”

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One reason why deaths are probably underreported is simple: there’s a lag between the data being collected and it being ready for publication. The data has to be collected from lots of different doctors and hospitals, aligned so it covers the same time period and verified for accuracy.

And there are even more fundamental problems that complicate things even further. For one thing, it’s not always certain what counts as a Covid-19 death. What if someone suffered from a severe health condition, such as cardiovascular disease or asthma, which was aggravated by Covid-19? Of the 3,912 deaths involving Covid-19 that occured in March, ONS reported that 86 per cent of cases died directly because of it – however, 91 per cent of those had coronary heart disease or other pre-existing conditions.


In hospitals, patients are tested and clinicians can list Covid-19 as the underlying cause on a death certificate even if the patient ultimately died from pneumonia or organ failure. This seems like a plausible chain of events. Yet, a clinician might think someone dying from a heart attack wasn’t the result of Covid-19 and would therefore not report it accordingly. “Often we, as clinicians, have to make judgments on these things. It's not as exact science as you'd want,” says Amitava Banerjee, associate professor in clinical data science at University College London and a cardiologist who has been drafted into the new NHS Nightingale Hospital.

Issuing death certificates becomes even more complicated when a person wasn’t tested for coronavirus, but was a suspected case. The latest ONS data shows there were 16,387 deaths up until April 3 – 6,082 more than could be expected at this time of year – and one in five deaths mentioned Covid-19.

Jason Oke, a senior statistician at the Nuffield Department of Primary Care Health Sciences in Oxford, says there may well be more unreported cases where Covid-19 was involved in the death but the individuals were never tested. Researchers and authorities may be able to fill some of these gaps in the future by tapping into the NHS’s 111 call log. “Obviously, if there's no trace of it, if they've never phoned 111, they've never contacted their GP, then I suppose they could get missed,” Oke says.

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Banerjee and his colleagues at UCL have modelled excess deaths – the difference between the expected number of deaths and actual deaths – over one year from Covid-19 based on the prevalence of underlying health conditions of different age groups in England. The findings, which will be published in The Lancet journal in late April, suggest there may be an excess of 14,000 to 70,000 deaths depending on the population infection rate and the impact of Covid-19 on the health system. To put this into context, Public Health England has been tracking flu-associated excess deaths for years and there are usually around 17,000 cases in a winter season. The full damage caused by Covid-19 can only be analysed in the future.


While any death involving coronavirus is counted as a Covid-19 death and reported publicly during the pandemic, categorising it as a direct cause of death will have an impact on our understanding of the disease in the long term. That’s where Banerjee sees a great opportunity for collaboration between different scientific fields. “It would be interesting in future research to try and understand whether Covid actually in its own right, for example, predisposes to heart attack or heart failure, or whether it's the other way around that heart failure is something that worsens the prognosis and the course of Covid infection,” he says.

There are also the indirect mortality impacts that the Covid-19 pandemic might have. Lockdowns and overstretched healthcare services could contribute to a person’s deterioration of health and subsequent death, but may not be mentioned on their death certificate. People may not have been able to attend their regularly scheduled doctor visits or stayed away from A&E for fear of being a burden. Over half of British adults (53.1 per cent) say the pandemic is affecting their wellbeing and data illustrating how social distancing measures and unemployment are impacting depression, suicide rates and other mental health issues are expected to emerge in the coming months.

“You might think it's pretty straightforward that when the economy takes a downturn and people lose their jobs, they're not going to be able to provide for themselves, and that's gonna have negative effects on health and survival,” says Jonathan Fuller, who trained in medicine and now works as a philosopher of science at the University of Pittsburgh where he seeks to understand how epidemiological evidence influences thinking in healthcare. An independent analysis looked at the correlation between unemployment and mortality during the 2008 recession and suggested that, somewhat surprisingly, overall death numbers went down in EU countries during that period except for suicide. For instance, as people weren’t getting in their cars and driving to work because they had lost their job, they were less likely to get into a traffic accident.

As countries are still grappling with the Covid-19 pandemic and focusing on infection and death rates to feed epidemiological models and inform the public about their risk of disease, they may miss out on data illustrating these indirect impacts. This will make it difficult to make inferences about causation retrospectively.

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Still, infection and death rates help epidemiologists model the trajectories of a pandemic as it unfolds, and in spite of all flaws and uncertainties, will allow governments and health authorities to assess how effective lockdowns and other public health interventions were at saving lives. “In order to figure out whether or not that was the best thing we could have done and how effective those policies were, we're going to need to compare what actually happened to what might have happened in a different hypothetical world,” says Fuller.

But ultimately, Fuller says, the absolute number of deaths will be the number that matters most. “It's those individual lives that actually matter. It's those individual lives that are cut short, and families that are torn apart.”

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