The balance between high levels of vaccination and high levels of Covid-19 in the community has “tipped in the wrong direction” in the last 10 days, Prof Philip Nolan has stated.
The surge in cases, with 2,180 reported on Saturday, the most since January, has put the full reopening of society next Friday in doubt.
It has also prompted deputy chief medical officer Ronan Glynn to advise workers to continue to work from home if they can during the winter.
Prof Nolan, the chairman of Nphet’s Irish Epidemiological Modelling Advisory Group since March 2020, has sought to explain why cases are so high at present, though 92 per cent of the adult population is fully vaccinated.
Ireland was at a disadvantage because it was hit by the Delta wave of the virus during the summer, he said. It drove daily cases from 300 to 1,800 per day during June and August, at a time when most of the population under 50 was not vaccinated.
The vaccination programme for young adults, aged between 16 and 30, saw a temporary decrease in Covid-19 numbers.
Prof Nolan continued: “However, this left us in a vulnerable position, with high levels of infection, and that delicate balance between very high levels of vaccine protection on the one hand, and increasing levels of social contact and risk of transmission on the other.
“The increase over the last 10 days shows that this balance has tipped in the wrong direction: with high levels of circulating virus [when] even a subtle change in the scale or nature of social contact can significantly shift the dynamics of viral transmission in the population.”
Prof Nolan said the autumn surge in cases was not as a result of the opening of schools.
“The incidence in schoolchildren was decreasing, and less than that in August prior to the reopening of schools despite higher levels of testing,” he tweeted.
There were “high but stable levels of infection last month” but it was a balancing act between the protection offered by vaccines and increased social contact creating opportunities for the virus to spread.
Nphet found evidence from the ESRI social activity measure and mobility data that mobility and social contact are increasing, and adherence to infection prevention measures decreasing.
A shift from outdoors to indoors may be playing a role, Prof Nolan said. Other seasonal factors might at play, but “their contribution at this point in time appears to be small”.
The average age at which people are being admitted to hospital with Covid-19 increased rapidly once young people were vaccinated in September, he said.
Prior to that some young people were admitted to hospital with Covid-19 but usually only for short stays.
“When the median age of cases increased in September, the probability of admission to hospital increased so, for the same case numbers, we saw progressively increasing numbers of admissions [now 35 admissions per 1000 cases],” Prof Nolan said.
“We can’t know what will happen over the coming weeks: this could prove to be a transient, or renewed and sustained growth in infections. We do know from past experience that when cases rise, people become more cautious and limit the spread.
“We can support and encourage those not yet fully vaccinated to reconsider that choice; and we cans support an encourage each other on the basics: self-isolate if symptomatic, masks, hand and respiratory hygiene, distance and avoid crowding, [use] ventilation.”
A further 2,180 Covid-19 cases have been reported on Saturday as a senior health official said high infection numbers were likely to continue in Ireland for the foreseeable future.
HSE chief clinical officer Dr Colm Henry said the State was unlikely to see "wild surges" in infections but that he expected they would continue to "rumble on" at a high level.
The latest Department of Health figures show 406 people with Covid-19 are being treated in hospital (down seven on Friday’s total) and that 71 are in intensive care (down two).
Currently Ireland has a 14-day incidence rate of 410 cases per 100,000 people and the recent rise in cases has led to uncertainty over whether the Government should proceed with plans to ease the majority of remaining pandemic restrictions from next Friday.
The National Public Health Emergency Team (Nphet) is set to meet on Monday to draw up advice for the Cabinet to consider before it makes a decision.
Alongside an outright pause on the planned easing up, it is understood options to be considered will include the retention of distancing measures in indoor settings like bars and restaurants across winter, allied to some increases in capacity in theatres and cinemas. A structured reopening of still-closed sectors such as night clubs may be favoured, again with retention of vaccination certs.
Dr Henry was asked on RTÉ Radio's Brendan O'Connor programme why the State has one of the highest rates of Covid-19 infection in Europe despite having one of the highest rates of vaccination.
It was suggested that this was an argument being used by anti-vaccine groups to encourage others not to get vaccinated.
Dr Henry said it was untrue to suggest that the vaccinations were not having a positive impact in the fight against the disease. He said there were almost 1,500 deaths from Covid-19 in January but that “we have a fraction of that now”.
“Similarly with admissions to ITU (intensive treatment unit), the link between cases and harms has been severely weakened, if not completely broken, and that is down to the vaccination programme.”
Cases are currently running at an average of some 1,500 a day, he said, and without the vaccine hospitals would be “over-run” with admissions as a result of Covid-19.
Dr Henry admitted that Covid-19 cases are “uncomfortably high” at present. He suggested that the rise could be attributed to greater levels of social interaction as society opens up.
He said he would be happy for night clubs to open provided entry was reserved for those with certs showing they had been vaccinated or had recently recovered from the disease.
“This will ultimately be a Government decision. It doesn’t have to be a binary decision. We have to make decisions based on the best evidence we have at that point in time,” he said.
“At this point in time, we are seeing a high level of cases, but they are not translating as badly as they used to in terms of hospitalisation. Nevertheless we still have people out there who are unvaccinated and are vulnerable.”
On Covid-19 testing, he said Ireland had an oversupply of PCR tests and this lessened the need for rapid antigen testing, which is being used in universities and childcare settings but not more widely in society.
He also said that there is "a big interest" in the booster vaccine programme. He anticipated that the National Immunisation Advisory Committee (Niac) will decide on Monday whether or not to expand the booster programme to the over 60s.
Government sources anticipate that Niac will give the go ahead for people aged over 60 to receive a booster dose, as well as frontline healthcare workers.
Dr Henry added: “I expect if there is a decision we will hear about it soon enough.”
Northern Ireland’s Department of Health on Saturday reported four deaths of patients who had previously tested positive for Covid-19 and a further 1,218 cases of the disease.