Chief Medical Officer Chris Whitty today said it is not yet known how long the Pfizer jab will stop people getting sick.
He said it was likely longer than nine months - but didn't yet know how long.
Prof Whitty told MPs social distancing restrictions could start being lifted once 20 million vulnerable Brits have been vaccinated.
Comment: "3 weeks to flatten the curve" - why would anyone believe anything they have to say now?
But he also said that could only happen "gradually" and not in the next three months. He warned "we're all very nervous about January and February" and said "I think it's very unlikely we'll get to zero level of risk."
Comment: There's no such thing as 'zero level of risk' in life, as an educated person he knows that.
Instead, Prof Whitty said, the government would likely choose to lift restrictions despite people still dying of Covid each year - like thousands already do from flu.
Comment: With every death now being assigned as coronavirus, this is the first year ever that almost NO ONE has died from the flu: Flu cases 'drop' 98% around the world
"We know these are very good vaccines to provide short to medium-term protection - we don't know how long that lasts," he told MPs. "It might last for a very long time, it might last for, you know, nine months. I think it's more likely to be somewhere between those two.
Comment: They do not know these are 'very good' vaccines, they know very little about them having only performed a few small scale trials, that's why the government needed to give Pfizer's concoction unprecedented emergency authorization bypassing standard procedures. And it's because of this concern over their safety and efficacy that some countries, such as Switzerland, are waiting for the UK experiemnt to get underway before they decide if they'll use them.
"In that case we may have to have a situation where we have to be in a position to re-vaccinate, particularly, the people who are most vulnerable."
Comment: We could be looking at a massacre.
Prof Whitty said the length of protection would depend on two things - whether immunity fades in individual people over time, and whether the virus mutates.
Comment: That's strange, because as Whitty well knows, the virus has been mutating since its discovery.
Neither of those things are known yet. Nor is it known yet whether the jab stops people passing on Covid-19 to others, rather than just getting sick themselves.
However, the Chief Medical Officer identified a potential threshold for easing lockdown rules in evidence before the Joint Coronavirus : Lessons Learnt inquiry.
Prof Chris Whitty told MPs 20million is the number of elderly people and those with underlying health conditions most likely to overwhelm the NHS.
Comment: 9 months have passed and hospitals have not been overwhelmed at any point during this manufactured crisis: Empty Hospitals? Where Are All The Coronavirus Patients?
They are due to be vaccinated in the first wave of a jab rollout between now and Spring 2021.
He said: "Once you got to that stage, I think, a conversation about now what do we want to do next becomes a really important conversation."
He added: "At a certain point society, through political leaders... will say this level of risk is a level of risk we think it is appropriate to tolerate.
Comment: And democracy be damned - corrupt political leaders will decide what level of risk they think is appropriate for citizens. Meanwhile they've given themselves and their mates a 'get out of lockdown free' card: Sports stars and high-value business travellers exempt from UK's quarantine
"Just as we accept that in an average year, 7,000 people a year die of flu and in a bad flu year 20,000 people die of flu.
"That's just we accept that as that is what happens biologically.
"You say the risk is now low enough that we can largely do away with certainly the most onerous things we have to deal with."
But Prof Whitty suggested this point was unlikely to come until the busy January and February period for the NHS has been passed.
He said: "For the next three months we will not have sufficient protection."
He added: "It's like someone giving up a Marathon race at mile 16".
Prof Whitty said he expects to have "three or four" different vaccines approved in the UK by summer 2021 which would speed up any rollout.
Comment: Is that a hint that they may try to play this sadistic game into the summer?
Earlier, the head of the MHRA regulator would not say when the two other vaccine candidates - Oxford/AstraZeneca or Moderna - might be approved in the UK.
But Dr June Raine said her "very active review" into the Oxford jab will receive more data "in the coming days". And more data on the Moderna jab is expected in the coming weeks.
Prof Whitty told MPs: "The aim would be to roll out this vaccine and then any others that get a licence and are effective and safe.
"We expect by the middle of the year probably to have a portfolio of three or four vaccines which we can actually use."
It came as Chief Scientific Advisor Sir Patrick Vallance admitted there was "no really hard evidence" supporting a 10pm pub curfew.
Comment: Little of what is happening in this new abnormal is supported by evidence.
He told MPs "keeping people together longer in an environment where there's also alcohol is likely to increase risk."
But in a move that could anger Tory MPs who opposed the curfew, he said: "That was a policy decision around trying to reduce the potential of interactions.
"It's not something you can model with a degree of accuracy and say a particular time will give you a particular result."
Comment: Even if they had a model, one would be foolish to believe it: Pandemic pushers, economy destroyers and sold out science: Imperial College are still open for business
Elsewhere Dr Raine also told MPs the drug dexamethasone has saved more than a million lives around the world in treating Covid-19.
She told a joint session of the two Commons Health and Science committees: "Dexamethasone is the drug which reduces mortality in the seriously ill hospitalised patients.
"That was a gift from the UK to the world and it has saved probably in excess of a million lives."
UK regulators today issued a warning that people who have a history of "significant" allergic reactions should not currently receive the Pfizer/BioNTech Covid-19 vaccine.
Two NHS staff members who received the Pfizer/BioNTech vaccine suffered an allergic reaction, in cases flagged last night.
Prof Whitty told MPs: "The initial process very importantly picks up common side effects.
"But extremely rare but important issues, inevitably you accrue more information over time.
"The NHS through to the MHRA is in a very good position to make sure we can pick things up quickly, identify them, communicate them widely and ensure we improve practice."
Comment: See also: Four volunteers of Pfizer's experimental coronavirus vaccine developed Bell's palsy, regulator warns those with allergies to NOT take it