Prof. Ian Young: Levelling off in COVID due either to good weather or immunity among younger people
Health experts believe a plateauing of COVID-19 cases may have been due to either the recent heatwave or a degree of immunity among younger people.
The Chief Scientific Officer Professor Ian Young said both hypotheses were being examined.
Speaking at the Stormont Health Committee Prof. Young said that if the levelling out of cases was due to the recent spell of good weather they could be expected to rise again.
But Prof. Young outlined an alternative scenario in which young people who have been exposed to the virus have developed a degree of immunity to the illness.
This, combined with the high vaccine uptake among older age cohorts, could lead to a decline in cases.
Prof. Young said experts will be looking closely at community transmission levels this week to determine which scenario is likely playing out.
"As members will be aware there has been a progressive increase in case numbers throughout the month of July and the number of cases is now at around 60 per cent of the number in the previous wave.
"It has been rising with a doubling time of approximately seven to eight days but over the course of the last week case numbers appear to have plateaued and have levelled out," Prof. Young told the committee on Thursday.
"There are two potential reasons for that. Number one, it may be as a consequence of the most unusual weather of the last two weeks. You will be aware that in general the virus spreads less well when individuals are outdoors and also its spread is reduced in the presence of good ventilation.
"So we believe there has been a high level of outdoor interaction in the last two weeks and in addition almost everybody has had their windows open encouraging ventilation and air flow and there may have been a significant beneficial effect of those two things in terms of reducing the rise in case numbers," he added.
Prof. Young said that if that analysis is correct the upward trajectory of case numbers could be expected to resume this week.
There is the more optimistic scenario of a younger age demographic having achieve a high level of immunity by way of infection, as Prof. Young outlined.
"The second possibility is that there is a key sub group of the population who are mainly responsible for driving the epidemic. They would be younger people with large numbers of social contacts and if that sub group of the population achieves a high level of immunity as a result of exposure to the virus then the impetus that they provide to transmission will decline and we may see an ongoing decline in case numbers," he declared.
Health experts will not be certain which of these two theories is correct until they look at whether case numbers decline or continue to rise this week.
Prof. Young said that 'if case numbers begin to rise again as a result of the weather deteriorating then there would be a further increase in hospital admission and pressures after that'.
The number of COVID-19 patients in hospitals at present is approximately a third of the previous wave.
"The proportion of individuals who are identified as cases who become admitted to hospital is falling and has fallen as a result of the beneficial effects of vaccination.
"During the last wave in February we were admitting five to six per cent of cases to hospital and at present it's somewhere between three and four per cent of cases which are being admitted to hospital," said Prof. Young.
He told the committee that pressures on critical care is at the upper end of what was modelled for the summer, however, there is still only a third of the numbers in critical care that was seen during the last wave in the winter.
"We believe that is likely due to the fact that younger patients are now being admitted to hospital as cases and that the threshold for admission to critical care may have changed somewhat."