Balancing vaccination rates with the lifting of lockdown restrictions may mitigate COVID-19 transmissibility

1. According to the mathematical model, a one-month delay in lifting all restrictions may have decreased peak hospital admissions by three-fold.

2. Increased laxity in reopening can help to negate the negative impact of the delta variant.

Evidence Rating Level: 2 (Good)

Study Rundown: With the increase of vaccine availability in early 2021, the UK government designed a four-step out-of-lockdown policy for stepwise lifting of non-pharmaceutical interventions (NPIs) in March 2021. Sequentially, this included school reopening, outdoor hospitality and non-essential retail opening, indoor hospitality reopening, and lifting of all remaining restrictions. However, the emergence of the delta variant a few months after resulted in a rapid increase in COVID-19 cases. This mathematical modelling study aimed to assess the impact of the UK government’s four-step framework on easing lockdown restrictions in England, UK. Outcomes of interest included overall mortality and total number of hospital admissions. According to study results, there was significant uncertainty in determining the trajectory of the pandemic, given vaccine hesitancy and transmissibility of the delta variant. However, the stepwise reopening framework in tandem with increasing vaccination rates may have mitigated a substantial number of COVID-19 cases. In particular, a one-month delay of step four in the reopening policy, from June to July 2020, may have attenuated peak daily cases by three-fold. These findings suggest relaxation of lockdown restrictions should be balanced with rates of vaccine uptake, vaccine effectiveness, and potential variants of concern.

Click to read the study in The Lancet

Relevant Reading: Simulation-Based Estimation of SARS-CoV-2 Infections Associated With School Closures and Community-Based Nonpharmaceutical Interventions in Ontario, Canada

In-depth [retrospective cohort]: This mathematical model used factors such as hospital admissions, hospital occupancy, seroprevalence data, and population-level PCR testing to determine the trajectory of COVID-19 in England, according to various time frames of NPI relaxation. The first step of lifting restrictions began on March 8, 2021. The delta variant emerged in UK in April 2021, having a transmission advantage of 76% (95% credible interval [95% CrI] 69-83). Accordingly, step four of the framework, which was initially scheduled for June 20, 2021, was delayed by almost a month to July 19, 2021. The model predicted that lifting all remaining restrictions in June may have resulted in 3900 (95% CrI 1500-5700) peak daily hospital admissions. Instead, a delay in reopening reduced peak daily hospital admissions by three-fold to 1400 (95% CrI 700-1700). The current model was affected by transmission of delta variant and vaccine effectiveness. Overall, the proportion of active COVID-19 cases can be dramatically reduced by appropriate timing of NPI relaxation and continued vaccine rollout.

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