A combination of high levels of immunity and the reduced severity of the Omicron variant has rendered Covid-19 less lethal than influenza for the vast majority of people in England, according to a Financial Times analysis of official data.
But the speed with which Omicron infects people still pushed the total number of deaths this winter whose underlying cause was a main respiratory disease to 9,641 since the first week of January, 50 per cent higher than in a typical flu season despite lower levels of social mixing, the Office for National Statistics figures revealed.
The high degree of immune protection from vaccination and previous infection among England’s population formed the basis of the government’s decisions to end legally enforced self-isolation last month and scale back free testing from April 1 as part of its “living with Covid” plan.
However, experts said a recent increase in hospital admissions — possibly driven by decreased behavioural caution after the dropping of restrictions or protection from the booster waning for older age groups — highlighted the risk of the government’s strategy.
“Is Omicron the same as flu? No. But the vaccines have made the risks to the individual very similar,” said Dr Raghib Ali, senior clinical research associate in epidemiology at Cambridge university, who added that this made a “large spike” in hospital admissions or deaths “unlikely” while Omicron remained the dominant strain.
Chart showing that in England, Covid has grown gradually less lethal over the pandemic, mainly due to immunity, and is now slightly less lethal than flu on average
The proportion of people infected with Covid-19 in England who go on to die has dipped below that of seasonal flu, which has an infection fatality rate of roughly 0.04 per cent, for the first time during the pandemic, according to the FT calculations.
The infection fatality rate from Covid-19 fell more than 10-fold from a little more than 1 per cent in January 2021 to 0.1 per cent in July as the UK’s vaccination campaign was rolled out, and the emergence of Omicron brought about a further three-fold reduction.
For every 100,000 Omicron infections, 35 will result in death, while the equivalent number of flu infections will lead to around 40 fatalities, the data showed. Even among the over-80s, where about one-in-200 Omicron infections still results in death, this figure is now lower than the equivalent for flu.
Animated chart showing that when we were first exposed to Covid, it was almost 20 times as lethal as flu for the most vulnerable, but since then immunity, improved treatments and a less virulent variant have reduced its severity, meaning it is now slightly less deadly than flu even for older people in England
Peter Openshaw, professor of experimental medicine at Imperial College London, said the government’s strategy of treating Covid-19 similarly to flu by relying on public health messaging and targeted testing, instead of bigger interventions, was “risky” but so far “had gone according to plan”.
“If our immunity stays high, the infection fatality rate will stay low,” said Openshaw. But he added that, if waning immunity or a new variant cause problems, “we now have delays built into the system”. He added: “Winding testing down means it will take time to wind it back up.”
Downing Street said on Wednesday: “We still continue to see the effectiveness of vaccinations, and Omicron seems to be more mild for most people.”
After falling for the past two months since the peak of the Omicron wave, Covid-19-related hospital admissions are on the rise again across the UK. There were 8,153 admissions recorded in England in the week to March 7, up 21 per cent from the week before.
Chart showing that the number of new Covid cases in English hospitals is rising again among all age groups
However, more than two-fifths of Covid-19 patients in England’s hospitals are being treated primarily for something else, having incidentally tested positive upon admission.
Unvaccinated people accounted for 15 per cent of adult admissions across England between late January and late February, according to UK Health Security Agency data, despite making up just 9 per cent of the adult population at the start of the period.
Christina Pagel, professor of operational research at University College London and a member of the Independent Sage group of scientific experts, said Omicron’s rapid transmissibility meant “the threat of Covid could still not be equated to flu”. This was especially the case because the BA. 2 sub-variant, which is about 30 per cent more infectious than the original Omicron, was dominant in the UK, added Pagel.
Pagel attributed the recent rise in hospital admissions to a mix of waning protection from the vaccines, the spread of BA. 2 and the end of most Covid-19 measures giving the virus more chance to infect people and cause severe illness. “I would be really surprised if we have a massive new wave. I wouldn’t be surprised if we end up having what we had with Delta where we get stuck at a high plateau for months and months on end,” she predicted.
Chart showing that although Covid is much less lethal than a year ago, it still elevated winter respiratory deaths by around 50 per cent compared to a typical flu season
Despite vaccination blunting Omicron’s lethality, its fast-spreading nature meant the total number of deaths whose underlying cause was either Covid-19, flu or pneumonia has still been 50 per cent higher since Omicron took hold in early December than over the same period during a typical flu season. The total respiratory disease fatalities were also 30 per cent higher than even during historically bad flu seasons, such as 2014-15 and 2017-18.
This represents a steep reduction compared to the previous winter’s Alpha variant wave, when there were about seven times as many deaths caused by any of the three respiratory infections, but nonetheless demonstrates that coronavirus is still adding to the winter disease burden.
However, Cambridge university’s Ali said that now that the risk of Covid-19 and flu were “in the same ballpark” it was “reasonable” for the government to “strike the right balance between preserving people’s freedoms and protecting those who are most vulnerable”.
Professor Julian Hiscox, chair of infection and global health at Liverpool university, cautioned against “complacency” over the reduced threat from Covid, adding that the offer of an additional spring booster should be widened from just over-75s and immunosuppressed people to all over-50s.
“We want to avoid dithering with the extra booster now and then getting caught on the back foot,” said Hiscox, who warned that “all of this could be academic if a new variant comes along”.
This article has been amended to correct the infection fatality rate of seasonal flu. The first chart has been amended to reflect the corrected range of the IFR.
Methodology: how the FT calculated infection fatality rates for Covid-19 and flu
The infection fatality rate (IFR) for Covid-19 was calculated using a numerator of deaths where Covid-19 was mentioned on the death certificate, and a denominator of estimated total infections from the ONS infection survey, both for England.
To account for the lag between infection and death, infections were shifted forwards using a log-normal distribution with an average of 26.8 days, based on prior academic research by Simon Wood. For any given date, deaths were then divided by lagged cases to arrive at the IFR.
For flu, the methodology was adapted from prior work by Marc Bevand. The starting point was the US CDC’s estimates of age-specific total symptomatic influenza infections and deaths in the 2019-20 flu season.
To move from symptomatic infections to total infections in line with the definitions used for Covid-19, the symptomatic figures were inflated to account for the fact that somewhere in the region of two-thirds to three-quarters of flu infections are asymptomatic.
The resulting figures for age-specific flu infection fatality rate (including asymptomatic infections) were then mapped onto the English population age structure to produce a population-level IFR for England.
If one assumes two-thirds of flu infections are asymptomatic, the resulting IFR for England is 0.0457%. Assuming three-quarters are asymptomatic gives an IFR of 0.0346%. The midpoint of these two estimates is 0.04%.
