How long will it take to get all vulnerable groups protected?
That’s the hundred billion dollar question! In theory, once all the top nine priority groups are protected, 99 per cent of all deaths can be avoided. That would remove the threat of the NHS being overwhelmed and allow the government to open up again. The target date for getting all those nine groups (about 25 million people) their first shot is the end of April. By the end of July they should all have had a second shot a be fully protected.
I sense a “but” coming on, what is it?
Unfortunately, there are a few – and they add up. In trials, there has not yet been a single Covid death recorded in a fully vaccinated individual. This is excellent but it is unlikely to hold up in the real world where efficacy may be lower. Also, “offering” jabs is one thing, getting everyone inoculated another. If you assume vaccine efficacy against severe disease at 90 per cent and take-up of the vaccine at 85 per cent, that still leaves 25 per cent of the population vulnerable. It may also be that the vaccines are less protective in the old.
Does this matter if we stamp out the virus?
No, if the vaccines prove efficient at slowing transmission of the virus and drive the R rate below one, herd immunity will have been reached and the epidemic will fade. Even if there are some who remain unprotected, they will be protected by the herd. The trouble is vaccines need to be highly efficacious in stopping transmission if this is to hold true.
Any clues on how good vaccines are at blocking transmission?
Oxford AstraZeneca said on Tuesday its vaccine was 67 per cent effective at blocking infection and this may translate into an even higher number when it comes to blocking transmission from one person to another. This is excellent news but the Warwick modellers calculate you would need 85 per cent of onward transmission to be blocked by vaccines to bring R below one – and even then some social distancing measures would be required.
The Warwick team sound like doomsters. Are others more upbeat?
There is a consensus it will take time to get to herd immunity but some are more hopeful. Modelling released on Thursday by University College London suggests herd immunity in the UK could be reached by mid-July given a fair wind.
Professor Karl Friston, the director of the Wellcome Centre for Human Neuroimaging, developed the model, and said it was intended to combat catastrophic thinking and give people hope.
His model makes a number of optimistic, but not unreasonable, assumptions, including that one dose of vaccine can give sterilising immunity (protection against transmission and disease) and also that lockdown is eased gently and sensibly, beginning with the reopening of schools next month.
“Just knowing that there is another way of picturing the future over the next six months is reassuring,” he said, acknowledging that the predictions could be wide of the mark.
Others said the approach used by UCL had a history of being over-optimistic, and Professor Mark Woolhouse, infectious disease epidemiologist at Edinburgh University and a member of Sage, said it remained very uncertain when – and even if – herd immunity might be reached.
“More pessimistically, it might not be possible to reach the herd immunity threshold at all,” he cautioned, although he stressed that this does not mean the Covid-19 cannot be brought under control. Rather, it means additional measures – things like face masks and regular testing and isolation for cases, rather than the current mass restrictions – will be needed to do so.
How do we judge who is right?
Professor Danny Altmann, an immunologist at Imperial College, said it remained almost impossible to call, although vaccines had brought enormous hope.
“Are there people imagining that by the end of the summer we never have to remember Covid ever again?” he said. “Or will it start to drift into something like an endemic coronavirus? Or will it be worse than that – we never really conquer it, and it’s like flu but worse, with 20,000 excess deaths forever and that’s part of normal life? I don’t know.”
What else must the Prime Minister consider?
As Prof Whitty keeps saying, there are many other pressures bearing down on the prime minister. Chief among them are the economy and schools. After the first wave of the virus, Mr Johnson opened the economy up only to have to close it down again. He wants to make sure the same mistake is not made again. Even the Treasury gets this. It may worry about scientists moving the goalposts but knows we can not afford a fourth spike in the virus. “This needs to be the last time we do this. This is the fat lady sings moment. We can’t lock down again”, one of Mr Sunak’s advisors told the Telegraph yesterday.
So where does this all leave us, when will lockdown be wound down?
The government has said it will publish an exit plan on February 22. Assuming infection rates continue to fall from their January peak, it seems a reasonable bet primary schools will open again in early March and secondary schools soon after. There is, after all, a national consensus that education is an overriding priority.