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How big a threat is Omicron to Ireland?

Analysis: Small fraction of serious cases would put health service under severe strain

Just weeks after the world first learned of the Omicron variant of Covid-19, a picture is emerging of the threat it poses to individuals and to health systems.

Unfortunately, the variant is moving faster than the corpus of scientific knowledge, so countries are having to make difficult decisions on the basis of the limited information available so far.

It seems clear from early indications that Omicron is more transmissible than previous strains, which is why it has overtaken the Delta variant in South Africa and is well on the way to doing the same in parts of England.

By how much? Estimates vary – one UK expert has estimated it is two to three times more infectious than Delta; Japanese scientists analysed South African data to come up with an estimate of 4.2 times more transmissible.

These differences are probably not all that relevant now, given the inevitability that Omicron will become dominant. Within a week, it has gone from an estimated 1 per cent to 14 per cent of Irish cases, and in Denmark and the UK it is possibly within days of achieving dominance.

This means there is very little point in Ireland continuing to apply travel restrictions to southern African states, given we have so many Omicron cases of our own.

The bad news around Omicron is not confined to its greater transmissibility. There is also evidence that it is better at evading the protection provided by vaccines, and also that it can lead to more re-infections of people who previously had the virus. One very small South African study (just 12 people) pointed to a big loss in efficacy of the Pfizer vaccine, with a 41-fold lower level of neutralising antibodies compared to an earlier variant.

This week, a larger South African study found that the Pfizer vaccine continues to give significant protection against serious illness, but this has fallen from 93 per cent with an earlier strain to 70 per cent with Omicron. Effectively, this means over four times as many people may not be protected against serious illness than before (30 per cent versus 7 per cent). It also reported high numbers of breakthrough infections in vaccinated people, with protection against infections reduced from 80 per cent to 33 per cent.

The analysis showed protection against hospital admission is maintained across all ages, with slightly lower levels of protection for older people.

Although the research was based on almost 80,000 cases linked to Omicron, these were not confirmed cases and the results must be regarded as preliminary.

However, some scientists have expressed concern about the possibility of “co-infections” occurring in society with both the Delta and Omicron variants circulating.

The most encouraging early indication has been that Omicron has for the most part been associated with mild illness. The same South African study found Omicron was 29 per cent less severe than the first wave the country endured last year.

There may be many reasons for a finding of reduced severity, for example, South Africa’s young population and the fact that most of its population has already been infected. Re-infections are usually milder.

It may be too soon to draw firm conclusions, due to the time lag between cases and the onset of serious illness. Omicron may behave differently in a highly vaccinated population such as Ireland than it does in South Africa, where barely one-quarter of the population is immunised.

If Omicron does rip through the Irish population, even a small fraction of serious cases would put the health service under severe strain. When cases are sky-rocketing “it’s about volume, not percentages” as Prof Tim Spector, professor of genetic epidemiology at King’s College London has noted.

Although cases in the UK have been doubling every two days, the rate of growth has slowed slightly in recent days. Growth has also slowed in South Africa and Denmark, but again this is too recent a trend from which to draw any firm conclusions. It might be just because people are taking more precautions, or because the virus is moving into different populations.

It does seem that the rise in Omicron cases is leading to fewer hospitalisations and ICU admissions than might otherwise have been expected. The drive to give people boosters will further depress the rate at which cases translate into patients requiring hospital beds.

Ireland had been doing reasonably well over recent weeks in controlling the current wave of Delta-variant cases, pegging infections by imposing relatively light restrictions.

What will happen now as Omicron takes over remains uncertain.