Here is why it is incredibly difficult for the government to announce a firm timetable for reopening schools, and why a decision to vaccinate all teachers before others could actually make it riskier to reopen them.
1) Although infections are falling in the UK, as a direct result of lockdown, the R according to official estimates is between 0.8 and 1, and the level of infections remains very high (the average daily number of positive tests per day, which will understate the true rate of injection, is 36,000).
2) The best estimate of the impact on the rate of transmission, or R, of closing schools is to reduce it between 0.2 and 0.5, according to the government Scientific Advisory Group on Emergencies (SAGE).
3) So reopening schools now would mean that R would almost automatically rise above 1 again, and infections would start to increase again, from a dangerously high base.
4) Hospital admissions are falling, especially in London, the East of England and the south east. But they remain nationally at a very high level. If the rate of infection starts to surge again, hospitals would not cope.
5) On the other hand, vaccinations are proceeding at a very rapid rate, well over three million a week at the current daily rate of not far off 500,000 per day.
6) So the government is highly likely to succeed in hitting its target of having offered a first dose of vaccine to the top four priority groups by 15 February (these groups are residents in care homes and their carers, those over 80 and front line health workers, those over 75 and those over 70, plus the clinically extremely vulnerable).
7) On the assumption that 70% to 80% of these priority groups accept the invitation to be vaccinated, we should see an accelerated reduction in the number of people dying of Covid-19, because even the first dose of vaccine has a dramatic impact on the risk of becoming acutely ill, within around two to three weeks of having the dose.
The point is that almost 90% of Covid-19 deaths have occurred among those currently prioritised for the vaccine.
8) But - and I know this sounds counterintuitive - this does not mean it would obviously be safe to reopen schools in or around 8 March, or three weeks after that 15 February target for completing the first phase of the vaccine roll out.
9) The biggest reason why it may not be safe is that - as I have been banging on about - 54% of people in struggling intensive care wards are aged between 50 and 69 (according to authoritative data from the Intensive Care National Audit and Research Centre).
Only a minority of people in intensive care are 70 and older.
And on the current timetable, vaccinations may only just have started for the over 65s by March, and not for anyone younger, unless they have serious underlying health conditions.
10) The vast bulk of infections is spread by those younger than 60.
11) We don't even know whether vaccinating people significantly reduces their ability to spread the virus.
12) So if the top aim of the lockdown and vaccination is to prevent the NHS falling over, if the primary concern is to make sure the health service can continue to treat everyone who is sick, then it would be dangerous and even perhaps reckless to ease lockdown in any substantial way until the vaccination of those over 50 is well under way.
13) One implication is that it would actually be less safe and less wise to reopen schools if all teachers were vaccinated now or soon as a priority, rather than all people over 60 and over 50.
There is a powerful case for making sure all teachers over 50 are vaccinated as soon as possible, but not for vaccinating literally every teacher at the same time.
14) In other words, although there is a powerful moral case for giving priority to all key workers (police officers, postal workers, bus drivers and so on) for access to vaccines, if opening schools is the aim, then it would be bonkers to vaccinate them before vaccinating people from all walks of life (including care workers) aged 50 to 70.
15) Maybe a sensible government policy would be to say that when it comes to vaccinating those aged 50 to 70, key workers among those should be at the front of the queue.
16) If the government went hell for leather to vaccinate all 16 million people aged between 50 and 69, that would take around five weeks at the current vaccination rate, if every dose was allocated to them.
17) But every dose can't be allocated to them, because the 12 million to 15 million people vaccinated in this first round all need to have a second dose with three months of the first dose.
18) On the assumption that the vaccination rate can be increased to 4 million a week, and half of that is used for first doses and half for second doses, it would take two months from mid February to vaccinate everyone aged 50 to 69.
19) Based on those assumptions, it should be safe to reopen schools in mid April, after the Easter holidays.
If the vaccination programme can be accelerated, it could well be possible to reopen some schools from mid March onwards - but that requires the vaccine to be targeted ruthlessly at those most vulnerable to hospitalisation, rather (and the ethics and politics of this are very hard) than those on the front line of providing vital public services.