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As the dark nights of winter keep on drawing in, any glimmer of hope on Covid really is welcome. Today, there were several shafts of light coming from the end of the tunnel, although blurred by the inevitable caveats and qualifications.

First, the coronavirus vaccine developed by Pfizer and BioNTech reported a 95% effectiveness (including among adults over 65 years old). It is set to be given emergency approval in the US “within days” and our own MHRA regulator looks poised to fast-track its own authorisation. Matt Hancock’s hope of getting it to the most vulnerable from December 1 may even be met.

Second, the cheaper and easier to administer Oxford/AstraZeneca vaccine is due to report its phase 3 trial progress very soon. Given that the UK has ordered 100m doses of this vaccine (we have ordered 40m of the Pfizer one) that would be another huge morale boost.

Third, and this is the most tentative glimmer of hope of all, today’s UK daily Covid case number dipped below the magic 20,000 level (to 19,609). That matters because it is the lowest daily total since November 2 and well below the rolling seven day average. One day’s number can never be relied on but if it is followed tomorrow with a lower number, the corner may finally have been turned.‌

On Monday, NHS Test and Trace’s Susan Hopkins had said that if the lockdown is working “we will start to see cases decline over the next week”. Everyone in No.10 and outside it will be hoping that her assessment is right. At a separate briefing today, Hopkins and deputy chief scientist Angela McLean said a family Christmas was “possible” as long as people followed the rules.‌

But here’s where the good news is tempered with cold reality. Both scientists stressed that tight restrictions may be needed before and after any Christmas break in order to keep the virus under control. And then Hopkins came out with her striking line that for “every day that we release, we will need two days of tighter restrictions”.‌

With the overnight speculation that a five-day loosening for Christmas was likely, that suggested a 10-day tightening afterwards. But when Public Health England told SkyNews later that in fact the Sage research (as yet unpublished) suggested five days for every day of relaxation, we were suddenly looking at a 25-day mini-lockdown to pay for the festive excess. That’s quite the New Year hangover.

The difficulty with this 5:1 ratio in the Sage research is of course that it suggests that any relaxation after December 2, when the current lockdown (McLean had to correct herself for using that word today, hastily using the No.10 approved “national measures” instead) may need some lengthy correctives.

With “non-essential” high street shops relying on even a slimmed down Christmas shopping season, will they face a long closure period in January? If pubs and restaurants reopen for a few weeks, will they then have to shut down again in 2021? Given that Liverpool’s Tier 3-plus seems to have got case numbers down, we could see that in other parts of the country. Prof Neil Ferguson has suggested hospitality should stay closed before Xmas.

The encouraging news for Boris Johnson is that the lag in the system means that for a couple of weeks after the lockdown ends on December 2, the case numbers could keep coming down. The danger is that the relaxation would kick in around December 16, the week before Christmas when many may be hitting the streets hardest in search of shopping or entertainment.

If there is on top of that another relaxation on household mixing (and on the Rule of Six) to allow for larger family gatherings for five days over the holiday period itself, there could be a bumper bulge in numbers that only a really tough January and February could counter. The prospect of a mini ‘third wave’ of Christmas Covid suggests a government policy process that would make a yo-yo diet look healthy.

Of course, the simple fact may be that Johnson is preparing for a Christmas relaxation simply because he believes most of the public will take matters into their own hands anyway. Better to tweak the rules than have them bent or broken, the logic goes. Also, schools being off for a fortnight may help counter the short relaxation in other rules.

But at some point the PM may have to “level” with the public that tight restrictions short of full lockdown may have to stay in place until those vaccines come properly on stream in the Spring.