The government will stick to its original timetable for lifting lockdown restrictions even though the vaccine rollout is on track to exceed the government’s own modelling assumptions, Downing Street has confirmed.

When Boris Johnson announced his long-awaited “roadmap” in February, many FactCheck readers asked us: why is it taking so long?

As we reported last month, scientists told ministers that moving too quickly could trigger a third wave of infections with more deaths and hospitalisations than we saw in January.

In a key paper presented to the SPI-M advisory group on 17 February, experts modelled what could happen if we eased restrictions at different speeds.

As we’d expect with this kind of analysis, the models made certain assumptions, including about the speed of the vaccine rollout, how many people would take up the offer, and how effective the jabs would be.

The rollout speed assumptions were “based on two scenarios, provided by the Cabinet Office, that may not reflect the situation most likely to occur”, the scientists wrote.

In the more optimistic of the two routes, we’d reach 4 million jabs per week by 25 April and sustain a level just below that through May. (The scenarios only differed on their assumptions of what would happen after that).

A lot has changed since that paper was produced. It now looks like we’re going to meet – and perhaps even pass – the 4 million threshold much earlier than those models assumed.

On 2 March, NHS England bosses wrote to regional directors to say that vaccine supply would “increase substantially” from 11 March and be “sustained at a higher level for several weeks”.

They said services should plan to deliver “around twice the level of vaccine available in the week of 1 March”. Assuming that doubling applies in all four nations, that works out at about 4.2 million jabs across the UK.

It was reported yesterday that NHS sources expect vaccinations to top 4 million this week.

That’s about six weeks earlier than was assumed in the SPI-M models on 17 February.

And it’s not just the number of jabs that’s going better than expected. There’s also some evidence that they’re more effective against infection and serious disease than was assumed in the SPI-M paper.

We put all this to the government. A spokesperson told us: “Having taken advice from our medical and scientific experts the dates set out in the roadmap are the earliest that any changes will take place.

“There will be a minimum of five weeks between each step, four weeks for the data to reflect changes in restrictions then followed by seven days’ notice of the restrictions to be eased”.