Non-pharmaceutical interventions, vaccination and the Delta variant: epidemiological insights from modelling England’s COVID-19 roadmap out of lockdown

Abstract

BackgroundEngland’s COVID-19 “roadmap out of lockdown” set out the timeline and conditions for the stepwise lifting of non-pharmaceutical interventions (NPIs) as vaccination roll-out continued. Here we assess the roadmap, the impact of the Delta variant, and potential future epidemic trajectories.MethodsWe extended a model of SARS-CoV-2 transmission to incorporate vaccination and multi-strain dynamics to explicitly capture the emergence of the Delta variant. We calibrated the model to English surveillance data using a Bayesian evidence synthesis framework, then modelled the potential trajectory of the epidemic for a range of different schedules for relaxing NPIs.FindingsThe roadmap was successful in offsetting the increased transmission resulting from lifting NPIs with increasing population immunity through vaccination. However due to the emergence of Delta, with an estimated transmission advantage of 73% (95%CrI: 68-79) over Alpha, fully lifting NPIs on 21 June 2021 as originally planned may have led to 3,400 (95%CrI: 1,300-4,400) peak daily hospital admissions under our central parameter scenario. Delaying until 19 July reduced peak hospitalisations by three-fold to 1,400 (95%CrI: 700-1,500) per day. There was substantial uncertainty in the epidemic trajectory, with particular sensitivity to estimates of vaccine effectiveness and the intrinsic transmissibility of Delta.InterpretationOur findings show that the risk of a large wave of COVID hospitalisations resulting from lifting NPIs can be substantially mitigated if the timing of NPI relaxation is carefully balanced against vaccination coverage. However, with Delta, it may not be possible to fully lift NPIs without a third wave of hospitalisations and deaths, even if vaccination coverage is high. Variants of concern, their transmissibility, vaccine uptake, and vaccine effectiveness must be carefully monitored as countries relax pandemic control measures.FundingNational Institute for Health Research, UK Medical Research Council, Wellcome Trust, UK Foreign, Commonwealth & Development Office.Research in contextEvidence before this studyWe searched PubMed up to 23 July 2021 with no language restrictions using the search terms: (COVID-19 or SARS-CoV-2 or 2019-nCoV or “novel coronavirus”) AND (vaccine or vaccination) AND (“non pharmaceutical interventions” OR “non-pharmaceutical interventions) AND (model*). We found nine studies that analysed the relaxation of controls with vaccination roll-out. However, none explicitly analysed real-world evidence balancing lifting of interventions, vaccination, and emergence of the Delta variant.Added value of this studyOur data synthesis approach combines real-world evidence from multiple data sources to retrospectively evaluate how relaxation of COVID-19 measures have been balanced with vaccination roll-out. We explicitly capture the emergence of the Delta variant, its transmissibility over Alpha, and quantify its impact on the roadmap. We show the benefits of maintaining NPIs whilst vaccine coverage continues to increase and capture key uncertainties in the epidemic trajectory after NPIs are lifted.Implications of all the available evidenceOur study shows that lifting interventions must be balanced carefully and cautiously with vaccine roll-out. In the presence of a new, highly transmissible variant, vaccination alone may not be enough to control COVID-19. Careful monitoring of vaccine uptake, effectiveness, variants, and changes in contact patterns as restrictions are lifted will be critical in any exit strategy.

Simulating the impact of vaccination rates on the initial stages of a COVID-19 outbreak in New Zealand (Aotearoa) with a stochastic model

“…The copyright holder for this this version posted November 24, 2021. ; https://doi.org/10.1101/2021.11.22.21266721 doi: medRxiv preprint controls were estimated for the original strain of Covid-19. 3 It is unclear if these values are appropriate for the more transmissible delta variant 8,20,21 or if population level controls are less effective against delta.…”

“…19 Furthermore, the effectiveness values used here for the population level 9 controls were estimated for the original strain of Covid-19. 3 It is unclear if these values are appropriate for the more transmissible delta variant 8,20,21 or if population level controls are less effective against delta.…”

Vaccinations or Non-Pharmaceutical Interventions: Safe Reopening of Schools in England

“…However, comparison of the resuse of NPIs in different countries suggest the same intervention in one country can have very different outcomes in others 37 . For the UK Sonabend et al 18 use a compartmental transmission model 38 and include the effect of VOC and a sterilising vaccine to explore a range of scenarios for relaxing restrictions from the period June -August 2021 18 . They include school reopening in their model but find that the large scale restriction relaxations have a dominating effect on increases in the reproduction number.…”

“…Our work is most similar in methodology to that of Panovska-Griffiths et al 17 , in assessing the most recent school reopening scenarios in the presence of various vaccination strategies. However, in comparison to theirs and other work (including Sonabend et al 18 ), our model allows more comprehensive representation of school interactions including inter-and intra-year group mixing, dividing children into classes, and greater control over possible interventions.…”

“…With schools reopening in England in September 2021, assessing the potential risks of reopening is crucial. Existing UK-based studies found a wide range of impacts of school opening in comparison to community transmission, ranging from significant 16,17 to negligible 18 , with only the latter study assessing the impact of school reopening in 2021 explicitly and none assessing their reopening in the context of the Delta variant. In this paper we focus on the relative importance of vaccination and NPIs in schools on pandemic progression in England during the latter half of 2021.…”