THE HEAD OF the country’s Covid-19 modelling group has said the measures in place in recent weeks are having a “very profound effect” on the transmission of the virus.
Giving an update at this evening’s Department of Health briefing, Professor Philip Nolan, chair of the NPHET Irish Epidemiological Modelling Advisory Group, shared an early run of the model his team has been working on, describing it as a “somewhat frightening scenario”.
“It shows what would have happened if the epidemic had been unmitigated,” he said.
“What this demonstrates is that this is not a question of simply flattening the curve, of pushing the peak out into the future, it’s a question of completely suppressing this disease, pushing down that curve so flat that there’s barely a peak detectable at all and we’re spreading a large number of cases out over a prolonged period of time,” Nolan said.
Nolan did not provide modelling for the current situation, with harsher measures in place, as he said the advisory group has more work to do on this.
This evening health officials confirmed a further 500 cases of Covid-19 in Ireland and another 28 deaths of patients diagnosed with the disease.
There are now 6,574 confirmed cases. Almost 53,000 tests for the virus have been conducted.
Nolan said the advisory group can see the “profound effect” the measures are having on transmission.
An important indicator in the epidemic is the effective reproduction number, he explained, which is the number of other people infected by one confirmed case. Social distancing measures reduce the opportunity for transmission and so reduce the reproduction number.
“At the beginning of the epidemic that was in the range of a little bit over four. When we closed schools we measured around 2.7. And we’re comfortable that number now is very close to one, so that each individual is infecting one other individual on average,” Nolan said.
“I say very close because that very close is critically important. If that number is even a little bit over one, cases will grow slowly but inexorably, if it’s a little bit less than one the number of cases will decline and it’s very sensitive to what that is,” he said.
There has also been a day-on-day reduction in the growth rate of the epidemic, from a 30% increase in confirmed cases per day at the start of the epidemic, to a 15% increase last week and over the last five days that growth rate has been 5%.
Nolan said the ICU figures are also encouraging, with a stable number over the last few days of 140 to 150 people.
“And if the disease is suppressed we will expect that number to decline over the coming week, or 10 days,” he said.
Nolan said the modelling does take into account the cases in the community that are not being tested and diagnosed.
I just want to reassure you that this model is robust to late tests or missing cases. In fact we assume that for every five cases we detect there are five cases we don’t detect, most of them – three or four cases – because they are asymptomatic or their systems are so mild they don’t come to attention of doctors – and one or two cases because of the limitations in testing capacity or that person simply didn’t get tested.
“So we model on the basis that we will not detect every case.”
Nolan said his group is looking at what is happening in countries like Austria, Norway and Denmark as they change their measures and it is modelling now what the future is going to look like if we maintain the current reproduction number of one.
“We’ve done extraordinarily well in getting the reproduction number down to one.
“We really need to keep that up, first of all to make sure precisely where we are, and secondly we will be requiring very strong social distancing measures for some prolonged period of time in order to keep the disease suppressed for the length of time that we need to.”
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