The impact of Christmas festivities on rising Covid-19 cases is set to be up to 15 times worse than pessimistic predictions made just weeks ago by public health officials leading the response to the pandemic.

In letters to Minister for Health Stephen Donnelly at the end of November and into December, chief medical officer Tony Holohan outlined gloomy forecasts on how case rates would surge after the festive period.

In his letter of November 26th, Dr Holohan said the National Public Health Emergency Team (Nphet) were modelling two scenarios during December – one with Level 3 restrictions in place, with hospitality closed and limitations on household visits, and the other with hospitality open and household restrictions eased.

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The first scenario would likely see an R number – a measure of how the disease spreads – of between 1.1 and 1.2, with the second and bleakest detailed scenario likely to see an R number of between 1.4 and 1.6.

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Nphet then modelled for “more intense” interaction as families and friends got together amid further eased restrictions between December 22nd and January 6th.

The predictions for this period over the Christmas holidays assumed an R number of 2 – meaning each infected person would spread it to two others.

The scale of the rise in cases as a result of the festive period would be dependent on which one of the two scenarios in the run up to December 25th preceded it.

Dr Holohan told Mr Donnelly that if the worst of the two detailed scenarios prevailed – an R rate of 1.4 to 1.6 before Christmas – then a rapid acceleration of the disease could be expected with “beyond 400 cases per day in very early January 2021”.

Latest predictions by Nphet that up to 6,000 cases a day could be reported over the coming days is a 15-fold surge on the 400 case a day scenario.

In November, Nphet was recommending Level 3 restrictions for much of December and January – with further easing between December 21st and January 3rd “in recognition of the societal importance” of Christmas.

Although it warned the epidemiological situation was "fragile" and Ireland remained very vulnerable to a "sudden sharp increase" in case of coronavirus.

On December 3rd, Holohan told Donnelly that daily case numbers were declining but model projections of the disease’s likely future trajectory had worsened over the preceding week as it seemed unlikely the daily rate was going to fall below 200.

Nphet projected at the time that the R number would be between 1.2 and 1.4 through Christmas and New Year, which it said suggested there would be between 300 and 600 new cases a day by the second week of January.

However, it added: “This is likely a conservative projection”.

But again, looking at the possibility of the R number rising to 2 – assuming relaxed restrictions between December 22nd and January 6th – its scenario was far short of the current daily rates.

Under this prediction, Nphet suggested there would be between 300 and 450 cases a day by New Year’s Day and between 800-1,200 a day by the second week of January.

By December 10th, Dr Holohan was simply warning the Government that modeling analyses show a “high risk” of a surge in new cases by January.

A week later, when the R number was estimated at between 1.1 and 1.3, modeling was again pointing to a high risk that “transmission into early January may impact further on public health”.

With daily rates at the time rising rapidly, Nphet said the situation was “considerably more concerning than had been projected at the end of November.”

Four days before Christmas, the Government was warned the situation was “deteriorating rapidly” amid clear signs of exponential growth in the spread of Covid-19 which was “similar or worse” than the second wave.