If one is to believe a British study of more than 1.5 million people who suffered from Covid-19, nature might have done as much as human technology to temper the global SARS-CoV-2 pandemic that has of this writing killed nearly 6.1 million people and left hundreds of millions more living in fear.

The peer-reviewed study published this week in The Lancet, a respected medical journal, reports the so-called omicron variant – the latest evolution of the Covid-19-causing coronavirus first discovered in China in December 2019 – is nearly 60 percent less likely to hospitalize people than the Delta variant that preceded it.

Were this not enough, the study says that among those hospitalized after infection with omicron there was a “69 percent lower risk of death than that of confirmed delta cases.”

The virus would appear to be tracking the second-best-case scenario virologists and evolutionary biologists outlined in a paper published in Nature last summer.

They conceded then that it was possible the pandemic could continue at a terrifying level for a long time, but observed that the  “second and more likely scenario is the transition to an epidemic seasonal disease such as influenza. Effective therapies that prevent progression of COVID-19 disease (for example, monoclonal antibodies that reduce hospitalization and death by 70–85 percent) may bring the burden of SARS-CoV-2 infection to levels that are equivalent or even lower than influenza.

“However, we should remember that the annual mortality burden of influenza, in non-pandemic years, is estimated to be between 250,000 and 500,000 deaths, with up to 650,000 all-cause deaths globally, comprising around 2 percent of all annual respiratory deaths (two thirds among people who are 65 years and older). This is an extremely important health burden and equates to a relatively ‘optimistic’ view of the future of the COVID-19 pandemic.”

There is, of course, the possibility of an even better evolutionary shift.

“A third scenario is the transition to an endemic disease similar to other human coronavirus infections that have a much lower disease impact than influenza or SARS-CoV-2,'” the pandemic forecasters wrote in Name. “There is, however, limited data on the global burden of disease by common human coronaviruses and as noted above, it is not possible to predict with confidence whether further adaptations of SARS-CoV-2 to humans will increase or decrease its intrinsic virulence.”

Those other coronaviruses are associated with what is known as the “common cold.”

No guarantees

Unfortunately, the evolutionary track of the common cold coronaviruses stretches so far back into human history that it disappears. The common cold viruses could always have been mild, or they could have once been deadly – like SARS-CoV-2 – and become less virulent as they evolved.

From a simple evolutionary standpoint, infectious viruses increase their chances of survival if their hosts survive. Viruses have a hard time growing and spreading if their hosts die quickly after infection.

This is believed to be one of the reasons the first SARS-CoV virus – now referred to as SARS-CoV-1 – could be snuffed out early in the 2000s. It lasted only from November 2002 to  January 2004 in which time it “killed 774 people – a small number in comparison with the fatalities during the previous pandemics of plague and influenza,” researchers reported in late 2004 in a peer-reviewed paper in the journal Nature Medicine.

“Asymptomatic infection seemed to be rare,” they added, and a large number of those infected with the disease were soon prevented from easily spreading it because of the severity of the infection.

“Around 20 to 30 percent of individuals with SARS require management in intensive care units, and the overall fatality rate is approximately 15 percent,” the study reported.

Still, the virus did have some things in common with less deadly SARS-CoV-2 to follow. Individuals with low counts of T cells – the body’s natural disease fighters – and older people were most vulnerable to SARS-CoV.

The vulnerability of older people to both SARS-CoV-1 and SARS-CoV-2 is linked to immunosenescence, the natural deterioration of the body’s immune system as people age.

Both a lack of exercise and weight gains to the point of obesity – two medical problems that now go hand-in-hand with the so-called sedentary lifestyle epidemic in the Western world – are known to accelerate immunosenescence and increase the risks for what is now widely termed “metabolic syndrome.”

Long linked to heart disease and stroke, metabolic syndrome has complicated the SARS-CoV-2 pandemic and played a significant role in the deadliness of SARS-CoV, though it was not the only factor that put people at risk from that novel disease.

“The age dependence of disease severity and mortality is notable,” the researchers studying SARS-CoV wrote.  “During the outbreak, mortality rates of affected individuals in Hong Kong who were 0–24, 25–44, 45–64 and greater than 65 years old were 0 percent, 6 percent, 15 percent and 52 percent, respectively.

“None of the 1–12-year-olds infected with SARS-CoV in Hong Kong had disease severe enough to require intensive care or mechanical ventilation. This progressive age dependence in mortality is not totally explained by comorbid factors and the underlying biological basis remains unclear.”

SARS-CoV-2 would later mirror these connections to comorbidities and age. Older people have been at greater risk of death from SARS-CoV-2-caused Covid-19 since the pandemic began, and they remain at greater risk even though the omicron variant is far less dangerous than earlier variants.

Continuing evolution

Whether omicron will remain the dominant form of SARS-CoV-2 remains to be seen, and the collection of United Kingdom researchers reporting in The Lancet noted the difficulty in predicting nature.

A variant of the variant has already appeared in the UK. Labeled omicron BA.2, it is pushing infection rates up again in that country where BA.2 is reported to be about 30 percent more infectious than the original omicron, now known as BA.1.

It is also better able to avoid both vaccines and immunity from previous infections.

UK health authorities are now pondering boosters for the last vaccine booster and pondering the issue of protection thanks to earlier omicron infections.

“I think the jury is still out on this last question, and I’ve certainly heard quite a few anecdotal reports of people coming down with covid recently for the second time in a few months, but there is some evidence to support the idea that such reinfections should be relatively rare,”  Colin Angus, senior research fellow at the University of Sheffield’s school of health, today told the BMJ (formerly the British Medical Journal). ” I’m cautiously optimistic that we might start to see a downturn in cases soon, but I think there’s still a lot of uncertainty around what will happen in the coming weeks.”

Whether BA.2 is more or less virulent than BA.`1 remains to be seen.

“It is not inevitable that viral evolution leads to lower severity,” the researchers reporting in The Lancet observed. “The risk of hospitalization appeared to increase when comparing delta with alpha infections and when comparing alpha with previously circulating lineages.”

They also noted that even though omicron is far, far less dangerous than delta was, there is a downside in that it is also easier to catch.

“Lower severity also needs to be counterbalanced against the ability of (the) variant to evade pre-existing immunity and thus transmit more readily within highly immune populations,” they wrote. We find evidence of moderate reductions in the protection vaccines provide against hospitalization in breakthrough omicron cases compared with that of delta, and previous studies indicate substantial reductions in vaccine effectiveness against symptomatic infection.

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