How long might this lockdown last?

Even though England’s lockdown laws are set to end on March 31st, Prime Minister Boris Johnson has said it is “too early” to know whether it will be possible to lift restrictions by the spring. However, when addressing MPs in the House of Commons, Health Minister Matt Hancock listed four measures that would need to be met in order for lockdown to be eased. These were that (1) there is not another major new variant that is causing difficulties; (2) the vaccination programme is working; (3) the number of hospitalisations is coming down; and (4) the number of deaths is coming down.

Interestingly, there was no mention of case numbers in the government’s criteria, even though they present a real-time measure for understanding the virus’s prevalence in the community. As we saw after the easing of the second national lockdown in December, lift restrictions too early and case numbers will take off again. Therefore, looking at cases numbers is important as it gives us the earliest indications as to when lockdown could be first eased. The question thus centres on how long it could feasibly take us to get the virus down to a low prevalence in the community. Below, I explore some possible time scales and highlight the challenges and opportunities that could delay or speed up the process.

DEFINING ‘LOW PREVALENCE’

As a society, we have had a polarised debate on what constitutes an acceptable level of transmission in the community. On one end of the spectrum are the lockdown sceptics who would prefer to have high levels of community transmission as long as the vulnerable are shielded or protected, while on the other are those who favour elimination and argue for a zero-covid approach, which would see extremely low levels of transmission as acceptable. This polarisation has prevented the middle group from gaining recognition in the debate. It consists of people who class themselves as “covid centrists” and who would prefer having certain thresholds of infections, hospitalisations and deaths defined so that, if passed, they would lead to a strengthening of restrictions.

This blog post is not concerned with arguing the pros and cons of each approach, but the debate is integral to the eventual easing of lockdown – whenever that may be – because it requires us to set parameters. What is an acceptable level of transmission in the community? While giving a timescale for the easing of restrictions may be unwise given the pandemic’s quick-changing nature, having targets to aim for – no matter how arbitrary – is not. Thus, when estimating how long this lockdown might last, we need to set a target to aim for, one that would indicate the virus was at a low enough prevalence in the community that the easing of restrictions was safe. The example I have used for my three scenarios is 50,000 cases per week (~7,000 cases per day).

MODELLING THREE SCENARIOS

In the previous two lockdowns, the weekly decline in cases has typically fallen between 15%-25%. Therefore, to demonstrate how long it might take for case numbers to return to “more acceptable” levels, I have modelled three scenarios using: (1) a consistent 15% weekly decline in cases; (2) a consistent 20% weekly decline in cases; and (3) a consistent 25% weekly decline in cases. This has been done over a 12-week period (18th January – 11th April) and uses the 266,156 cases by specimen date for the week of 11th-17th January as its base figure.

Here is the table detailing how the decline in England’s weekly positive cases would play out in the three scenarios.

Credit: Anna Woodberry

Here is the graph showing how the decline in England’s weekly positive cases would play out in the three scenarios.

Credit: Anna Woodberry

WHAT DO THE THREE SCENARIOS SHOW?

Unfortunately, given the high number of cases in England before we went into lockdown on 4th January, it is going to take several weeks for the number of infections to drop to a more acceptable level. For example, to reach the 50,000 cases per week initial target in each scenario, it would take:

  • 11 weeks (end of March / beginning of April) in Scenario 1 (15% decline)
  • 8 weeks (middle of March) in Scenario 2 (20% decline)
  • 6 weeks (end of February) in Scenario 3 (25% decline)

Given we saw a ~20% decline in cases from the week of 4th-10th January (335,069 weekly cases) to the week of 11th-17th January (226,156 cases), the middle option appears most realistic. Though it is important to remember that, in reality, the decline in cases won’t be consistent. Nonetheless, keeping an eye on how much cases decline over the next few weeks should provide more data on how long lockdown might be needed.   

However, the scenarios also demonstrate the potential benefit of staying in lockdown past the 50,000 cases per week target, providing greater reassurance and protection moving forward. Over the whole of the 12-week period:

  • 15% decline would get you <40,000 cases per week (<6,000 cases per day)
  • 20% decline would get you <20,000 cases per week (<3,000 cases per day)
  • 25% decline would get you <10,000 cases per week (<1,5000 cases per day)

Whether the government choose to follow a more cautious path or give in to pressure from the lockdown-sceptic fraction of the Conservative Party remains to be seen.

WHAT COULD SPEED UP THE PROCESS?

Vaccinations present the greatest opportunity to speed up the decline in transmission. Even with imperfect protection (one dose instead of two) and prioritising the most vulnerable, they will play an enormous role in our fight against coronavirus. As the number of people vaccinated increases, the R rate should decrease, providing less opportunity for the virus to transmit in the community. Over the next few weeks, scientists and mathematicians should be able to start quantifying the effect of vaccinations on our daily figures and will help form the foundation for the easing of restrictions.

WHAT COULD DELAY THE PROCESS?

Given the importance of education, getting children back into school will be one of the first priorities for any easing of restrictions. However, the school environment provides the perfect breeding ground for the virus (even with measures in place). When schools – and universities – went back in September, we saw incredibly high increases in infections (90% weekly increase, followed by 25%, 40%, 50% and 75%). Thus, allowing schools to return could still be hugely problematic for keeping a lid on transmission, especially as children are not included in the vaccination programme. This could be helped by further pushing levels of infection down to ensure the virus is at low prevalence in the community, though this would mean more weeks in lockdown for the general population.

Mutations also pose a significant risk to our progress. There are early concerns that the South African and the Brazilian variants could provide some resistance to vaccines. This demonstrates the risk mutations play in our hopes for returning to normality. A vaccine-resistant mutation could suddenly halt the world’s progress, providing another argument for aiming for a very low prevalence of the virus in the community as it presents less opportunity for the virus to mutate. Similarly to the vaccination data, the work conducted by scientists on these mutations will form the bedrock of any lockdown exit strategy.

REMAIN CAUTIOUSLY OPTIMISTIC

Though England will remain in lockdown for several more weeks to come, there is still a reason to be cautiously optimistic. The daily vaccination figures show that the government is currently on target to meet its promise of vaccinating the first four priority groups by mid-February. This will provide increased protection for the most vulnerable moving forward, even against the current mutations, as currently there is no variant known in the world that would counteract the vaccine. Fingers crossed things stay that way and the second half of 2021 can be better than the first.    

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