COVID-19: Omicron now less deadly than flu?

While it does not mean this will be true everywhere else in the world and under all circumstances, the numbers are significant.

What does it mean?

One report, based on UK population data, clearly indicates that on a per-infection basis, COVID now makes it less deadlier than the seasonal flu.

The report, published by Financial Times on March 10, analysed the evolution of COVID infection fatality ratio (IFR) relative to seasonal flu in the UK.

This reflects what most epidemiologists say — that the coronavirus would eventually become a cold-like virus as the population develops immunity, through vaccines or natural infection, or both.

One sign of its infectiousness: Science Direct recently reported that “incidental COVID cases” have gone up, referring to asymptomatic patients hospitalised for other complaints, but with incidentally-discovered COVID-19, which usually comes with mild or moderate lung involvement.

Is it the same everywhere?

This COVID-is-less-lethal-than-flu phenomenon observed in the UK requires confirmation in bigger population-wide studies.

Vaccine experts have stated that mass vaccination drive has reduced the fatality rate by 11-fold. Boosters also helped as the emergence of the highly infectious Omicron reduced it by another 4-fold.

Still, the UK report is significant as it sets a milestone: that widespread immunity (through previous infection and/or vaccination) and the emergence of a less virulent variant in Omicron has helped the population reach this stage.

Dr Monica Gandhi, Professor of Medicine at the University of California, San Francisco, said the report cited a “really important data."

Seasonal flu death rate

In the US, the CDC reports that deaths from influenza and pneumonia is 16.3 per 100,000 (or 0.053%). In 2020, it caused 53,544 deaths, and ranked No. 9 among the top causes of death in the US.

Flu alone, killed 1.8 persons per 100,000 people in 2020, according to CDC data.

The flu season occurs annually during a time period characterised by the prevalence of a flu outbreak, usually during the cold half of the year in each hemisphere. 

COVID deaths

Officially, COVID has caused 453 million infections and over 6.03 million deaths as of March 11, 2022 since it was first reported in December 2019, according to Johns Hopkins tracker data.

A new study, however, puts the number of deaths at 18 million, three times higher than the official toll recorded by most trackers.

South Africa data

The UK report echoes an observation made earlier this year by another researcher.

On January 3, 2022, Dr Paul Glasziou, a clinical researcher at Australia’s Bond University, made a rough calculation which showed the risk of death with Omicron has gone down even lower than that of the seasonal flu.

Using data from the CDC, WHO and NCBI, Dr Glasziou compared flu vs COVID data based on several points — infection rate, incubation time, hospitalisation rate and case fatality ratio.

In a back-of-the-envelope calculation, Dr Glasziou showed that among the vaccinated (using the Gauteng, South Africa data), Omicron had a CFR of less than 0.1% — less than the CFR for the seasonal flu (0.1%). However, among the unvaccinated, Omicron CFR was up to <0.5%.

The computation was “rough”, he explained, citing many confounders — detection, age, vaccination.

“Bottomline,” he stated, “for unvaccinated, Omicron better than delta (~1/3 hospital/death) worse than ’flu. For vaccinated, less than ’flu,” Glazsziou wrote in a twitter thread.

Only half of the picture

The analysis is significant as it mined data on total deaths caused by major respiratory diseases — flu, pneumonia and COVID — over the last 8 years. However, the report warned that looking at the IFR is only "half of the picture", as the total toll from COVID infections will have a bearing the the mortality numbers.

So even if a virus is less lethal on a “per-infection” basis, the report noted, it can still cause more deaths overall — if it infects more people, especially in places where vaccination rate is low, or the shot used is not the most effective. Last winter, COVID increased mortality risk enormously: or 7 times more deaths than in a typical flu season, the report noted.

This winter, the picture has changed dramatically, though in January/February 2022, COVID increased the winter respiratory death toll by around 50% compared to a typical year.

Rise in UK COVID infections

Based on the UK data, the infection fatality ratio from COVID-19 fell more than 10-fold from a little more than 1% in January 2021 to 0.1% in July as the country’s vaccination drive was rolled out. In addition, the emergence of Omicron brought about a further three-fold reduction.

The recent rise in cases in the UK has come as a surprise.

However, while flu is typically wanes by March, the number of COVID-positive patients in hospitals has risen in the UK, where health authorities reported one in 25 people was estimated to have had coronavirus last week – levels last seen in the middle of February.

COVID-19 cases in Hong Kong are also spiking, with a high number of severe cases in hospitals, and soaring deaths. One reason: too few of the older people in Hong Kong are vaccinated, the New Scientist reported. Other European countries, notably Germany, have reported a rise in hospitalisations.

Dr Michael Daignault, an emergency physician, cited an “odd phenomena of hospitalisations rising BEFORE cases. Lots of theories but 60% incidental COVID (highest % yet) offers best explanation!”

Washington University study

In a related study, researchers at Washington University modelling the pandemic’s next stage expect Omicron to lead to 99% less death than Delta. So if the latest dominant variant is 99% less deadly than Delta, this suggests the current IFR with Omicron could be as low as 0.0025%, the equivalent of 1:40,000, the model shows.

Some experts say while this is possible,this is highly unlikely across the board, given the variability in immunity, mixing and other factors.

Instead, they said the actual figure from the Washington University model could be about 0.07% — meaning a ratio of approximately 1:1,430 people who get infected will die due to the illness.

By comparison, leading researchers estimate flu’s IFR to sit between 0.01% and 0.05%. They argue, however, that comparing rates for the two illnesses is not a straightforward exercise due to numerous variables.

Caveats

Before we celebrate this COVID-is-less-deadly-than-flu thesis, it pays to know a number of important caveats, the report stated.

(1) SEASONALITY: Flu tends to be seasonal. COVID is not only a threat during winter. If COVID cases jump again in the coming months, that would further increase mortality risk relative to flu, the report noted.

(2) MIXING: Work setting that reduced social mixing has continued to help reduce infection numbers.

(3) LOWER FLU NUMBERS: Total mortality from major respiratory diseases has actually been “lower” this winter than a typical flu season for young adults and children. That’s because of less flu/pneumonia compared to a pre-pandemic level of social mixing.