Relaxing lockdown measures on June 21 could result in a resurgence of infections and hospital admissions, government scientists in the UK have said.
However, the level of uncertainty around the modelling suggests it is not possible to tell if proceeding with the next step of the road map would result in a resurgence considerably smaller or larger than previous waves.
The main uncertainties lie around how much quicker the Delta variant first identified in India grows, and vaccine effectiveness against severe disease caused by the now dominant variant, and the extent to which behaviours and therefore transmission will change as measures are relaxed.
Figures released by Public Health England as Boris Johnson was due to set out plans for the next stage of easing restrictions suggest two doses of the Covid-19 vaccines are highly effective against hospital admission from the Delta variant.
All the scenarios modelled – by Imperial College London, the University of Warwick, and London School of Hygiene &Tropical Medicine (LSHTM), and considered by Government scientists – suggest even a short delay to the next step would result in a significant drop in the number of people being admitted to hospital.
This is because more people would be vaccinated as the school summer holidays get closer.
A Scientific Pandemic Influenza Group on Modelling, Operational sub-group (Spi-M-O) document dated June 9, released by the Government Office for Science, said: “Even a two-week delay would have a significant effect, but a four-week delay is modelled as reducing the peak in hospital admissions by around a third to a half.
The experts say that since the start of April 2021, the ratio of confirmed cases to admissions has been stable, and if this continues, each doubling of cases will lead to a doubling of admissions.
“The number of hospital admissions that are S-gene positive (and are therefore almost certainly the Delta variant) has been growing in recent weeks, however, this has been masked by a drop in those which are S-gene negative,” they add.
The scientists also say that the R value is estimated to be 40-80% higher for Delta than for Alpha, first identified in Kent, although a figure higher or lower than this cannot be ruled out.
The Warwick experts warn that although the majority of their analysis reflects the greater transmission advantage of the Delta variant, other novel variants may pose an even greater risk to the relaxation roadmap.
In particular, variants of concern with high levels of vaccine escape or where past infection does offer immunity could generate additional waves of infection on top of any predicted here.
They predict a large third wave of infections exceeding those in the second wave – but say that due vaccination, the number of hospital admissions is expected to be slightly lower, while deaths will be further reduced.
While modelling from Imperial released on Monday suggests that across all transmissibility and immune escape scenarios explored, the Delta variant could lead to a significant third wave of hospital admissions and deaths “similar to or larger than the winter wave”.
The experts say cases, hospitalisations, and deaths in the next month could grow rapidly, but delaying the June 21 relaxations should delay the projected third wave and reduce the estimated number of deaths and hospital admissions.
While LSTHM modelling says: “There is considerable uncertainty over the properties of the Delta variant, but all scenarios considered project a third wave of infection peaking in the mid-to-late summer if roadmap Step 4 is enacted on June 21.”
A document from the Scientific Advisory Group for Emergencies (Sage) dated June 9, and released on Monday, says: “Longer delays prevent more hospitalisations and deaths, but most of the benefit comes from the first four weeks of delay (from June 21) in the main scenarios modelled.
“This is partly because four weeks is a long enough to ensure significantly more vaccination coverage and would push step four close to the school holidays, when transmission is expected to be reduced.”
It continues: “Taking step 4 of the road map on June 21 carries significant uncertainty and risk.
“It is not possible at this point to determine whether this would result in unsustainable pressure on the NHS.”
A Government scientific adviser said there is a lot of uncertainty but they think the country may be one small, slightly extended wave, away from the end of the beginning – getting everybody through either their first infection or their first two doses.