Fewer Covid-19 deaths than expected in most optimistic scenario

Covid-19 cases, hospitalisations and ICU admissions were above the most optimistic projections, but deaths were well below expectations, according to the latest figures.

At the end of June Prof Philip Nolan's modelling group in the National Public Health Emergency Team (Nphet) presented four different scenarios for the months of July, August and September.

They ranged from optimistic to pessimistic, with two central scenarios depending on the scale of opening and transmission of the virus.

The most optimistic scenario envisaged moderate indoor mixing with a conservative estimate of the transmission of the Delta variant.

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The “Central No 1” scenario imagined high levels of indoor mixing and low levels of transmission. The “Central No 2” scenario imagined moderate levels of indoor mixing and and high levels of transmission.

The most pessimistic scenario involved higher levels of indoor social mixing and greater Delta transmission.

The number of Covid-19 cases in the three months was 117,148, according to figures based on the number of cases on July 1st versus the number on September 30th.

This is significantly more than the 105,000 cases envisaged in the most optimistic scenario, but a lot less than the next worst scenario with 185,000 cases. The most pessimistic scenario predicted 566,000 cases.

Social mixing

Prof Nolan said the pessimistic scenario was based on a level of social mixing which occurred at the end of the summer of 2020 when Covid-19 numbers were low, and the transmissibility of the Delta variant as it was then reported from the UK.

There were 2,107 admissions to hospital in the months of July, August and September, according to an analysis of the figures produced by the Health Protection Surveillance Centre (HPSC).

That is more than the 1,985 envisaged in the optimistic scenario, but a lot less than “Central No 1”, which predicted 3,455 hospital admissions. The most pessimistic prediction was for 10,730 hospital admissions.

There were 306 people admitted to ICUs in the three-month period, the HPSC figures suggest. This is more than the 260 as envisaged in the optimistic projections, but considerably less than the 445 in the “Central No 1” scenario.

There were 249 reported deaths between July and September. This was less than the 335 deaths envisaged in the most optimistic scenario.

Most publicity

The most pessimistic projection and the one which garnered the most publicity at the time was the prospect of 1,760 deaths through the three months.

In a lengthy Twitter thread published at the time the modelling was announced, Prof Nolan said it was based on the scenario that the Delta variant was between 40 and 60 per cent more transmissible than Alpha, which was dominant here at the start of this year.

The effect of the vaccination programme was also factored into the calculations.

At the time the Nphet projections were used to justify the delay in the opening of indoor hospitality, which was due to happen on July 5th but did not eventually happen until July 26th.

Prof Nolan said that “even the most optimistic scenario with the Delta variant shows opening on 5 July risks a significant surge in cases”.

At the time Prof Nolan said caution was “well-advised” because of the transmissibility of the Delta variant.