Not enough data to assess if Omicron is a threat, say scientists

Experts believe widespread immunity is the best way to end the pandemic

Indian students apply the finishing touches to paintings created to raise awareness of the variant in Mumbai. Reuters

International travellers wearing personal protective equipment arrive at Melbourne's Tullamarine Airport as Australia records its first cases of the Omicron variant. AFP

A greeting at the international terminal of Sydney Airport, as countries respond to the new variant. Reuters

A sign asking people to wear face coverings in a building in Manhattan as the newly discovered Omicron variant appears in countries around the world. AFP

Tourists wave as the ‘Europa’ passenger liner arrives in South African waters off Cape Town as the new coronavirus variant Omicron spreads in other countries. Reuters

Schiphol airport in Amsterdam. Dutch health authorities said they have found another case of the Omicron Covid-19 variant among passengers arriving from South Africa, bringing the country’s total to 14. AFP

Pupils wear face masks in Beijing. Despite the global worry, scientists say it remains unclear whether the Omicron variant is more dangerous than other strains of the virus. AP

People wearing face masks in Manhattan. New York's governor has declared a state of emergency due to the risk of a surge of Covid-19 cases as winter sets in. AFP

British Health Secretary Sajid Javid meets a member of staff at a vaccine centre in Guy's and St Thomas' Hospital, London. Getty Images

A sign points the way to a Covid-19 test centre at Schiphol Airport in the Netherlands. AFP

Narita International Airport in Japan is quiet after travel was restricted to prevent the spread of Omicron. Reuters

A PCR test at O.R. Tambo International Airport in Johannesburg. AFP

Soekarno Hatta International airport. Indonesia has banned the arrival of travellers who have recently been in eight southern African countries. Reuters

Suvarnabhumi Airport in Bangkok after Thailand banned entry from eight southern African countries due to the Omicron variant. Reuters

Travellers wear personal protective equipment outside the international terminal at Sydney Airport, Australia. Reuters

Passengers wearing protective gear at Incheon International Airport in South Korea, where health authorities have imposed an entry ban on foreign arrivals from eight African countries, including South Africa. EPA

Ben Gurion International Airport near Tel Aviv. The Israeli government approved a 14-day ban on foreign arrivals over concerns about Omicron. EPA

Travellers queuing in the hope of boarding an overbooked Lufthansa flight at Cape Town International Airport. Antonie Robertson / The National

Covid-stricken Czech President Milos Zeman sits in a plastic cage as he appoints Petr Fiala as Prime Minister, near Prague. AFP

Tourists checking in at Cape Town International Airport in South Africa. Antonie Robertson / The National

Several airlines have stopped flying out of South Africa amid the spread of the new variant, causing disruption at O.R. Tambo International Airport in Johannesburg. Reuters

Australian Health Minister Greg Hunt at a press conference at Parliament House in Canberra. Two cases of the recently discovered Omicron variant were detected in New South Wales. EPA

Passengers, many not wearing face coverings, on the London Underground. Health Secretary Sajid Javid said mandatory mask-wearing would return to shops and public transport in England but there are concerns over how the rule will be enforced. AFP

A stroll, with face masks, in Biarritz, south-western France. French Health Minister Olivier Veran said France had no confirmed cases of the Omicron variant and was not changing its strategy of increasing vaccinations and booster shots. AP

British Prime Minister Boris Johnson and Chief Medical Officer Chris Whitty during a press conference on the variant in London. Reuters

The heavily mutated Omicron variant has sparked concerns that it may evade the protection of vaccines – but there have also been suggestions the new version of the coronavirus may be less virulent.

Scientists currently have little data to go on, so hopes the new variant is not as likely to cause serious illness rests largely on reports from doctors in South Africa who treated early Omicron cases.

It will probably be weeks before researchers fully understand Omicron’s pathogenicity, transmissibility and ability to cause illness, even in vaccinated people.

But if it does represent a more mild form of the coronavirus, it could mean that the pandemic follows a pattern seen elsewhere, in which infections become endemic but less severe over time.

“If you think about the extremes, a virus that kills 90 percent of the people it infected would very quickly run out of people. It won’t have anywhere to go,” said Prof Ian Jones, a virologist at the University of Reading in the UK.

“On the other hand, a virus that you hardly notice you have, but was transmitted easily, would be transmitted over time. The tendency is for viruses to lose virulence and cause less severe disease. They become endemic.”

The idea that pathogens tend to become milder as time goes on, sometimes called the law of declining virulence, is often attributed to Theobald Smith, a celebrated American research scientist of the 19th and 20th centuries.

According to the theory, viruses spread more effectively if they replicate quickly but do not cause severe disease, at least in the early stages of infection. This is because if the hosts remain well, they can mix with others and spread the pathogen.

Several disease outbreaks appear to tie in with Mr Smith’s theory.

Among those often quoted are the “Spanish flu” pandemic of 1918, which is thought to have killed tens of millions of people around the globe. Some have suggested the virus gradually became less dangerous as the pandemic continued into 1920, when it ended.

Another example concerns a coronavirus that infects people, OC43. This may have caused the “Russian flu” pandemic of the late 19th century, which is blamed for at least one million deaths. Today, OC43 is much less deadly, as it is one of several viruses that causes the common cold.

While Mr Smith’s idea gained wide acceptance, in recent decades researchers have put forward other models that suggest a more varied range of scenarios, in which evolution towards reduced pathogenicity is not inevitable.

Among the ideas is that if pathogens are durable outside their host, they may be successful when they are both highly transmissible and virulent. Durability allows them to survive outside of their host for extended periods before finding a new host.

The myxoma virus, the cause of myxomatosis in rabbits, while often cited as a case where virulence has declined over time, may actually represent a more mixed picture.

Introduced to Australia, France and the UK in the 1950s, it initially caused devastation among rabbit populations, although as time continued, more rabbits survived infection.

This has been put down to both reduced virulence from the virus and increased resistance in the rabbit populations.

Researchers at the University of Oxford who published a study in 2019 tracing the evolution of rabbits in relation to myxomatosis noted, however, that more virulent strains of the virus have emerged in recent times. There is, they said, an ongoing “arms race” between the virus and the rabbit population.

Evidence so far with the coronavirus has suggested to some scientists that it is not becoming less harmful.

For example, as well as being highly transmissible, the Delta variant has been associated with a higher rate of hospital admissions (and transmissibility) than the Alpha variant, which emerged earlier.

Because the coronavirus spreads most readily in the early stages of disease, before severe symptoms develop, there may be little evolutionary pressure for it to become less virulent. Even if people subsequently fall severely ill and even die, the hypothesis suggests, the virus will already have spread.

According to Dr Andrew Freedman, an infectious diseases specialist at Cardiff University, in terms of evolution “it’s not inevitable” that the coronavirus will cause milder infections as time goes on.

“Mutations can make it more transmissible and virulent in the worst-case scenario,” he said.

If the coronavirus becomes endemic and milder over time, vaccination and natural infection (which confers immunity) are, he said, likely to be the key factors.

Prof Jones also emphasised the importance of widespread immunity in ending the pandemic.

“What will happen over time, the edge of the disease will fade further, as long as immunity is maintained,” he said.

In any case, Prof Jones said that, for the moment, it was unclear whether the Omicron variant causes less severe infection.

While doctors in South Africa have highlighted that cases have been mild, “exact data” has yet to be collected.

“Until we see a huge number of infections, I don’t see it’s a realistic assessment, especially in South Africa, where quite a lot of cases are not reported accurately,” he said.