Modellers believe third wave might not happen
New data shows vaccines have cut transmission of virus although regional differences remain
NEW modelling to be presented to ministers ahead of stage three of reopening on May 17 will show the risk of a “third wave” of Covid cases in the UK has diminished dramatically and may not happen at all, say experts.
The last set of projections, published by Sage on March 31, presented ministers with a difficult dilemma because they suggested a third wave could kill up to 20,000 people in the late summer if steps three and four of the exit roadmap were implemented as planned.
Ministers are expected to proceed with step three of the roadmap, with the return of indoor household mixing and indoor hospitality, as modelling teams which provided projections for ministers are said to be more optimistic.
Prof Adam Kucharski of the London School of Hygiene and Tropical Medicine, who works on modelling provided to Sage, welcomed the new real world data on vaccine effectiveness.
“There was considerable uncertainty about the impact of vaccines earlier this year, but recent studies are landing at the more optimistic end of the scale”, he told The Sunday Telegraph. “We could still see some increase in transmission as things reopen, but the resulting impact could be relatively low”.
New real-world data released last week has allowed Sage to improve the assumptions which underpin their models. Crucially, a PHE study showed for the first time that vaccines cut “breakthrough transmission” of the virus by about half after a single shot.
“If you look at where they were in early April, compared to where they were in early February, they moved a huge distance”, said James Ward, a mathematician and insurance risk manager, who runs his own Covid model which closely shadows the official ones.
“It’s not very far for them to move now, from predicting an exit wave of 15 to 20k deaths to predicting an exit wave of zero to 5k, or maybe nothing at all”.
Mr Ward’s own model already includes the now substantiated assumptions on vaccine effectiveness.
Sage will look at modelling provided by Imperial College London, the University of Warwick and the London School. All three provide a range of projections but it is their “central scenarios” on which Sage places most weight.
In March, the central scenarios of the Imperial and Warwick models projected the virus would die off by September if the exit plan was stopped at phase two, but that it would spike again in late summer if phases three and four were implemented.
The London School’s model used a much lower assumption for vaccine effectiveness, and projected a third wave as bad or worse than the one which swept Britain in December and January. If the new projections point up areas of concern, they will likely focus on regional and social differences in suppressing Covid-19.
Yorkshire, for instance, still has relatively high viral transmission. Sage will want to be sure that these differences do not spark localised spikes. Mr Ward added that ministers would also be keeping a close eye on vaccine uptake among the young.
This is important as the models depend on high uptake if we are to reach herd immunity.
“I’m optimistic but frankly it would be good to have a little bit of headroom above the herd immunity threshold so that we don’t either don’t have a winter wave or, if we have one, it is moderate”, said Mr Ward.
One way of creating that headroom if vaccine uptake is low among young adults would be to vaccinate children, he added.