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Chief Medical Officer Dr. Tony Holohan. Leah Farrell/
stark warning

From 250 to 2,170 deaths, here's what NPHET's modelling said about four 'Delta wave' scenarios

The Department of Health has published the letter from Dr Tony Holohan to the government.

NPHET’S ADVICE TO government contained four different scenarios for the next three months that modelled the potential of between 250 to 2,170 deaths. 

The Department of Health has published the letter from Dr Tony Holohan which Taoiseach Micheál Martin this afternoon described as “stark”. 

Cabinet today decided to pause the planned reopening of indoor hospitality and agreed to work on a plan that would see people who are fully vaccinated or had recovered from Covid-19 returning to indoor hospitality before a full reopening.  

The pause is based on the spread of the Delta variant of Covid-19 which Holohan said in his letter would “grow sharply over the coming weeks”. 

Holohan’s letter says that the variant is now thought to account for 97% of cases in the UK and that there is evidence it is more transmissible and that vaccines offer “somewhat less protection” against it. 

“What is clear is that the Delta variant, with it’s clear transmission advantage over the Alpha variant, is rapidly becoming the dominant strain, and in our partially-vaccinated population, the increased risk of onward transmission associated with this variant makes a significant fourth wave of infection likely,” Holohan says.

What is uncertain is the magnitude of this fourth wave, and its severity in terms of hospitalisation, mortality, and long-term sequelae.

While NPHET says it is”uncertain” about the magnitude of what the Taoiseach and Tánaiste referred to as a “Delta wave”, it offered a number of scenarios about what that magnitude could be. 

Those modelled scenarios are outlined in Holohan’s letter, four of the outcomes were based on different prevalences of the Delta variant while one “counterfactual scenario” modelled what would happen if there was no Delta variant introduced.

The four scenarios are as follows: 

  • An optimistic scenario with moderate indoor social mixing and conservative estimates of transmission advantage.
  • A first central scenario, with higher levels of indoor social mixing and higher estimates of transmission advantage.
  • A second central scenario, with moderate levels of indoor social mixing and higher estimates of transmission advantage.
  • A pessimistic scenario, with higher levels of indoor social mixing and higher estimates of transmission advantage.

In the letter, the CMO provided a modelled table about what each of those scenarios could look like in terms of cases and deaths from the beginning of July to the end of September. 


Both Taoiseach Micheál Martin and Tánaiste Leo Varadkar addressed the modelling presented to government by NPHET, with Varadkar saying the “optimistic” scenario was akin to a flu season while the pessimistic one was closer to the height of the Covid-19 pandemic.

“If you take the optimistic one, we’re talking about maybe 165 deaths over the next three months, roughly one or two a day, each a tragedy, each a relative, each a family grieving, but similar or not as bad as what you’d expect to see in the average flu season, and certainly not a reason to shut down a country,” he said.

On the other hand the pessimistic scenario is totally different, over 2,000 deaths occurring over a three month period. A wave as severe as any that we’ve experienced to date, with hospitals coming under enormous pressure and ICU is in particular. So with that in mind, bearing in mind that the pessimistic scenario is a potential outcome, we decided that we’re going to be cautious and we’re going to err on the side of caution.

He added: “It’s just not possible for us to know at the moment how long this Delta wave will last or how bad it will be. We will see that unfold in Scotland and in England over the next couple of weeks but we’re erring on the side of caution here.”

In terms of which scenario was more likely, the Taoiseach said that NPHET advised that the situation could “land somewhere between” the first central scenario and the second central scenario. 

Marin said that “what is clear” is that the reopening of indoor hospitality as had been planned made the more pessimistic scenarios more likely. 

“What is clear from NPHET’s advice is that if we were to proceed as we had planned in our entirety from 5 July onwards, we would significantly increase the risk of the more negative scenarios and the pessimistic scenarios that they have outlined, which really would have a very significant impact on people, on our health service and on mortality, and that was the context in which government took that advice,” the Taoiseach said. 

Note: The ‘optimistic’ projected figure of 165 deaths has been amended in this piece as it incorrectly appeared on the original version of the CMO’s letter. The actual ‘optimistic’ figure is 250.  

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