England’s COVID-19 roadmap succeeds in balancing transmission and immunity

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England’s COVID-19 roadmap succeeds in balancing transmission and immunity


England’s COVID-19 roadmap has succeeded in balancing increased transmission with population immunity, according to a major study.

The out-of-lockdown roadmap has managed transmission rates by balancing the increasing contact rates between the gradual reopening of society and the growing immunity of the population through vaccination, according to new analysis from the team at Imperial Oil’s COVID-19 response.

Dramatic reduction in risk

Delaying the lifting of all restrictions by one month until July 19, in response to the emergence of Delta, also likely significantly reduced the risk of a significant spike in hospital admissions in the fall / winter and reduction in deaths in the 12 months following June 2021 by approximately 20%.

While hospitalizations and deaths are still only a fraction of what they were in January, Delta means infections are currently higher than we would have hoped. Pr Neil Ferguson

The analysis, published in The Lancet, estimates that lifting all non-pharmaceutical interventions (NPIs) on June 21, 2021, as originally planned, could have resulted in more than 3,400 maximum daily hospitalizations due to the impact of the variant. Delta. The delay to July 19 reduced the potential peak in admissions by about three times.

Roadmap to get out of confinement

The government’s roadmap on getting out of lockdown for England saw four gradual stages of easing restrictions, starting on March 8 and ending with the lifting of all restrictions from July 19.

Researchers say that following step 1 of the roadmap on March 8, when schools and educational institutions reopened, the number of cases, hospitalizations and deaths continued to decline, as had been the trend during the full spring lockdown.

After Stage 2 on April 12, the R number for Alpha remained below one due to the increased immunity of the population through vaccination. Researchers estimate that the R number for Alpha remained below one until July 2021.

Delta variant

If Delta had not emerged, the planned roadmap to emerge from the lockdown would have been sufficient to keep cases, serious infections and deaths low and manageable. Dr Raphaël Sonabend

The Delta variant was detected in England in early April and led to a rapid increase in cases and hospitalizations from mid-May that was not fully offset by the vaccination program due to the increased transmissibility of the variant. and vaccines being less effective against it.

The increase in contact rates after stage 3 continued to be partially offset by the increasing immunity of the population through the deployment of the vaccine. However, while the effective R number for Alpha remained less than one, for Delta it remained greater than one.

Projections show that if the Delta variant had not emerged, lifting all restrictions as planned on June 21 would not have led to a substantial third wave.

European football tournament

A sharp increase in transmission was observed in early July, followed by a rapid decline after July 11. This suggests that the increase in transmission was probably primarily caused by a change in social contact rates, likely associated with the Euro football tournament, and not as a result of Stage 3 of the roadmap. This increase in the number of cases, along with evidence that Delta was more transmissible and potentially more severe than Alpha, resulted in Stage 4 being postponed for a month until July 19. This enabled the additional distribution of 2.8 million first and 3.8 million second doses of vaccine.

Recent trends in cases, hospitalizations and deaths through mid-August suggest that contact rates have increased gradually since stage 4 on July 19.

Fall and winter screenings

The team projects a fall wave of transmission, but with great uncertainty around the peak in hospitalizations and the resulting total number of deaths. This uncertainty is due to an imperfect knowledge of the efficacy of the vaccine against Delta, of the overall level of immunity of the population, which explains the decline in natural immunity and the imperfect cross-protection between variants, and the level of Diversity.

The team says the intensity of transmission in the coming months will depend on the increase and speed with which population contact rates increase, the roll-out of booster doses and adolescent vaccination, and respect for the isolation of cases.

Dr Raphael Sonabend said: “At each stage of the COVID-19 roadmap, we have modeled a wide range of scenarios to analyze how lifting the restrictions can change the course of the outbreak. “

“We found that lifting the restrictions in July, a month later than originally planned, was successful in reducing the risk of a big wave of fall infections, hospitalizations and death. If Delta had not emerged, the planned roadmap to emerge from the lockdown would have been sufficient to keep cases, serious infections and deaths low and manageable. The latest data demonstrate the importance of a gradual increase in social diversity to return to pre-pandemic levels. We remain cautiously optimistic and will continue to use our models to monitor the outbreak. “

Professor Neil Ferguson said: “Our analysis shows that the timing of the gradual easing of COVID restrictions to keep up with the vaccination rollout has been largely successful in limiting infection levels, although some additional challenges have been posed by the Rise of the Delta variant in May this year While hospitalizations and deaths are still only a fraction of what they were in January, Delta means infections are currently higher than we would have hoped. transmission over the next few months. “

Dr Marc Baguelin said: “In our study, we showed that, despite the lifting of restrictions, until the emergence of Delta in June, the R number remained below or close to 1 thanks to the vaccination program. Of the cases of the Delta variant, the mathematical models gave a strong signal that a month of delay was needed to catch up on vaccinations and put the roadmap back on track. While infections are still high, we are now in a much better situation than a year ago. One of the lessons of our work is that mathematical models can be extremely useful in informing policy makers when open and transparent collaboration is in place. “

Dr Anne Cori said: “The objective of the roadmap policy was to gradually relax restrictions that would reflect and be offset by the gradual increase in the protection of the population through vaccination, so that new infections remain at reasonably low levels. Our study shows that this objective would have been achieved if Delta had not seen the light of day. But Delta completely changed this balance between protection of the population and social mix, because the vaccines were slightly less effective against it, and above all, Delta was much more transmissible than Alpha. “

“Our study illustrates the role that mathematical models can play in informing the design, monitoring and evaluation of policies such as the road map. It also highlights the potential threat posed by the new variants and the need to regularly review policies in the light of new scientific evidence. We estimate that the postponement of step 4 of the roadmap following the emergence of Delta reduced the peak of hospitalizations by a factor of 3. ”

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