Experts on Omicron severity: positive signs or still too early to say?

Early evidence from South Africa, Denmark and the UK – countries that are higher up the Omicron wave than Ireland – suggests that this new variant will not be as severe as our four previous waves.

While this data from overseas hospital systems gives reasons to be hopeful heading into the Christmas period, despite the increased risks from greater household mixing, experts warn that there are many variables at play with Omicron and the full impact on the Irish healthcare system remains far from clear and may depend on how high case numbers ultimately go.

Studies suggest that despite being more transmissible, fewer Omicron-infected people will require hospital treatment. The estimates range from a 30 to a 70 per cent reduction.

Researchers in Scotland found there was a reduction of two-thirds in the number needing hospital treatment, but this study was based on a very few cases and few at-risk older people.

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A study from South Africa found that people there were 70 to 80 per cent less likely to require hospital treatment because the Omicron variant was not as severe as other variants and because there was a high level of immunity from vaccinations and previous infections.

Research published by the UK Health Security Agency on Wednesday night had similar findings: people catching Omicron are 50 to 70 per cent less likely to need hospital care. The agency did, however, warn that this could still lead to large numbers of people in hospital.

‘Numbers game’

Dr Corinna Sadlier, an infectious diseases consultant at Cork University Hospital, said the studies were "definitely positive" in suggesting that Omicron may be causing milder illness but the concern was "the numbers game" – the total number of infections.

“It is definitely positive that we are not seeing the same level of admissions that we saw with Delta but really it will be down to the overall numbers and the proportion that will end up in hospital. We don’t know what that will be. That will really depend on total cases,” she said.

Imperial College London found that Omicron's mutations have made it a milder virus than Delta, with the chances of a person ending up in a hospital emergency department being 11 per cent lower with Omicron than Delta if a person had no prior immunity.

The researchers concluded that UK population immunity from vaccinations and past immunity meant the risk of ending up in hospital was 25 to 30 per cent lower.

Given the high levels of vaccination in Ireland, where about 95 per cent of the population are vaccinated with primary doses and about half with booster doses, this should reduce the likelihood of hospitalisations from Omicron infections even more here.

Paul Moynagh, professor of immunology at Maynooth University, said the research showed Omicron was not as effective as older variants at infecting cells in the lower respiratory system that causes severe illness, and that T-cell (a type of white blood cell) protection from past Covid-19 infections and vaccinations would help protect people against severe disease from the new variant.

“All of that combined gives us confidence in terms of being able to control Omicron. Some will say that because Omicron transmits so well, that even a small percentage of those very large numbers ending up in A&E is still a problem,” he said.

“Nonetheless, the less severe nature of Omicron combined with the fact that the vaccines are standing up well against it in terms of protecting against severe illness is a good thing.”

Unvaccinated

Dr Sadlier cautioned that not everyone would enjoy the same level of protection against Omicron. She said that it was unclear how Omicron infections in the unvaccinated and the immunosuppressed with lower vaccine protection would translate into hospital admissions.

Then there was the challenge facing the health system: high levels of infections in the community might result in large numbers of healthcare workers being forced out of work.

“There is a lot of uncertainty and it is difficult to have contingency plans for all scenarios, including a scenario which would see a large number of healthcare workers infected with Omicron and out of work. That again will put pressures on the system,” she said.

Dr Annie Curtis, immunologist at the Royal College of Surgeons in Ireland, said there were reasons to be "very hopeful" in the data from overseas but warned that daily case numbers would "absolutely rocket" over the coming period, making booster vaccinations all the more important to protect people.

“There is cause for hope but I really would be careful about the narrative around this. There are so many forces at play with Omicron,” she said.