OMICRON NOW ACCOUNTS for around 35% of cases in Ireland, a figure that is expected to rise rapidly as has been seen in other countries.

The World Health Organisation (WHO) said earlier this week that the strain has been reported in 77 countries and has “probably” spread to most nations undetected at a higher rate than any previous variant of the virus.

EU leaders said yesterday that vaccinations and booster shots would be vital to counter the Omicron coronavirus variant as countries stepped up restrictions to slow its startling spread.

“It is spreading at the ferocious pace and potentially has a risk of escaping our vaccines, at least partially,” said EU commission president Ursula von der Leyen at the end of the talks.

Von der Leyen said projections suggested the mutated Covid strain could be dominant in the EU as early as next month.

Scientists remain uncertain how dangerous the highly mutated Omicron variant is, but early data suggests it can be more resistant to vaccines and is more transmissible than the Delta variant.

With this in mind, here’s what we know so far about Omicron and the efficacy of vaccines and boosters:

Transmissibility and severity

The WHO’s Covid-19 Technical Lead Dr Maria Van Kerkhove said the increased growth seen in the Omicron variant in comparison with other variants of concern is “some of the sharpest increases that we’ve seen to date”.

“We do know that it has what we call a growth advantage over Delta. And what this means is that we’re seeing a large increase in cases where Omicron is detected,” said Dr Van Kerkhove during a WHO update.

On whether Omicron will outcompete Delta to become the dominant strain circulating in populations, Dr Van Kerkhove noted that it’s still a bit early for us to have a full understanding but that some of the mutations that have been identified in Omicron so far “will provide a growth advantage that will allow it to be more transmissible”.

We’re also still learning about severity as well when it comes to Omicron.

Although Britain on Monday confirmed what is thought to be the world’s first Omicron death, there is no proof yet that the variant causes more severe illness.

The WHO on Tuesday provided room for cautious optimism saying Africa had recorded a massive rise in cases over the past week but a lower number of deaths compared with previous waves. But it urged countries to act swiftly to rein in transmission, protect their health systems and guard against complacency.

WHO expert Bruce Aylward strenuously warned against “jumping to a conclusion that this is a mild disease”.

“We could be setting ourselves up for a very dangerous situation,” he said.

Dr Van Kerkhove also stressed that even if the virus causes less severe disease it can still impact vulnerable populations: “We know people with underlying conditions people of advanced age, if they are infected with any variant of SARS-CoV-2 including Omicron, they are at an increased risk of developing severe disease.”

However, she said that given there is increased transmissibility “there will be more cases, more hospitalisations, and more hospitalisations that could put healthcare systems that are already overburdened into a state where people will not get the appropriate care that they need”.

“So it is really critical that even if we do see more mild disease, we still do everything that we can to reduce transmission in all populations, people who are vaccinated, as well as people who are not vaccinated.”

HSE chief clinical officer Colm Henry said yesterday: “There’s much talk about a weakened link between harm and cases, but we know from the Delta variant, if you have enough cases ultimately some of them will always translate into harm, whether it’s hospitalisation, or ICU.”

Vaccines and boosters

New research published today has suggested that Omicron largely evades immunity from past coronavirus infection or two vaccine doses, and boosters are key to mitigating the impact of the variant.

The risk of reinfection with Omicron is 5.4 times greater than that of the Delta variant, according to researchers at Imperial College London.

This suggests the so-called immunity protection against reinfection by Omicron may be as low as 19%. Pre-Omicron studies estimated that prior infection afforded 85% protection against a second Covid-19 infection over 6 months.

The study also found no evidence of Omicron having lower severity than Delta, but data on hospital admission was very low at the time of the study.

According to the data, boosters are vital in controlling Omicron, but they may lose some effectiveness over time.

Researchers estimated the proportion of Omicron among all Covid cases between November 29 and 11 December was doubling every two days up to 11 December.

Based on this they also estimate the reproduction number (R) of Omicron was above 3, over the period studied.

Professor Neil Ferguson from Imperial College London said: “This study provides further evidence of the very substantial extent to which Omicron can evade prior immunity, given by both infection or vaccination.

“This level of immune evasion means that Omicron poses a major, imminent threat to public health.”

There is a significantly increased risk of developing a symptomatic Omicron case compared with Delta for those who were two or more weeks past their second vaccine dose, and two or more weeks past their booster dose (for AstraZeneca and Pfizer vaccines), the report found.

It also showed that vaccine effectiveness against symptomatic Omicron infection of between 0% and 20% after two vaccine doses, and between 55% and 80% after a booster dose.

A separate report by Imperial researchers looked at the effectiveness of booster doses against Omicron, estimated that booster jabs could provide about 85% protection against severe illness from Omicron, and over 90% protection against death from the variant.

In a worst-case scenario, where the antibody decay rate after a booster dose is the same as that observed after the first two doses, the researchers predict that vaccine efficacy against severe disease may drop from 96.5% against Delta to 80.1% against Omicron, by 60 days after the primary vaccine course followed by a booster of the Pfizer jab.

If the rate of decay is half that rate, the drop is estimated to be from 97.6% against Delta to 85.9% against Omicron.

However, the researchers say that while these numbers are currently associated with a high degree of uncertainty, they indicate that Omicron-variant specific vaccines and/or further boosters are likely to be needed to restore protection.

- With reporting from PA and AFP