Scientists advising the government on coronavirus warned ministers two weeks ago that Christmas relaxation rules would hit the elderly worst.
In a set of documents released on Friday, the Scientific Advisory Group for Emergencies (Sage) said on December 2 that modelling studies suggest there may be a higher proportion of cases in older and more vulnerable age groups during the festive period, which could lead to an increase in hospital admissions.
“The more days over which additional mixing happens, the greater the increase in incidence in the over 65s,” it states.
Between December 23 and 27, families in the UK will be allowed to form a three-household bubble to celebrate Christmas – a policy announced by the government at the end of November.
But despite a rise in Covid-19 infections, Boris Johnson has decided not to change the guidance despite pressure from medical experts.
Sage also suggests avoiding social contacts for more than five days before meeting older or vulnerable people at Christmas may reduce the risk of coronavirus transmission.
It also said that a longer period – such as a week or more – of abstaining from social contact could reduce the risk even further when gathering with loved ones during the festive season.
Experts believe the typical incubation period of Sars-Cov-2, the virus that causes Covid-19, is around five days.
This is the time when a Covid-19 positive person is the most infectious.
A document published by Sage dated November 26 said: “Households are one of the main settings for transmission.
“Reducing the risk of transmission in households is therefore important for limiting spread of Sars-Cov-2, as is identifying where the first person in a household is infected and thus the routes by which infection gets into the household.”
It added: “Avoiding social contacts for a period greater than the typical Sars-Cov-2 incubation period (which is around five days) before meeting older or vulnerable people at Christmas will reduce the risk to them.
“A longer period (eg a week or more) would reduce the risk further.
“This point should be considered in relation to families and preparation for Christmas.
“This is also relevant for other celebrations and observances and beyond the Christmas period.”
They also said other modelling research suggests taking a rapid coronavirus test – such as a lateral flow test – before a multi-day gathering inside a home may be of benefit to those involved.
However, they added that lateral flow tests “should not be seen as a way on its own of enabling high-risk activities to take place but could reduce the risk of activities being undertaken”.
It comes after another document released by Sage last week showed the tests missed around 51% of all cases.
The experts said that mixing between households over the holiday period for one or two days would be less risky than multiple households spending the entire time together.
A document dated December 2 said: “Preliminary analysis from one modelling group suggests that if additional mixing is restricted to three households meeting per day and to the five-day window of relaxations, the total number of days spent mixing within that period may have a large impact on post Christmas prevalence.”
But the scientists added that the outcome of relaxation of coronavirus rules over the festive period remains “highly uncertain”.
They said: “The rules in place would greatly restrict mixing compared to most years; if adherence to these restrictions is high then it is highly unlikely that the prevalence will double.
“Transmission to elderly and more vulnerable people might increase the incidence of disease more than the incidence of infection.
“Healthcare seeking and testing-seeking behaviour will change over the festive period.
“This, and possible disruption in data cycles, mean that it could taken several weeks to fully understand what happened in that time.”