Containment vs delay: what’s the difference

There has been a lot of talk in the news in the last couple of days about how measures to deal with the spread of coronavirus COVID-19 are likely to move from the ‘containment’ phase into the ‘delay’ phase in the next few days. But what’s the difference?

Basically, the containment and delay phases do exactly what they sound like. Containment means that there are a small number of cases, and measures are taken to try and contain the virus and prevent it spreading. These include immediate testing of anyone at risk of being in contact with the virus; quarantine in isolation centres for those returning from high-risk areas; rigorous contact tracing for anyone who tests positive; and the closure and deep cleaning of any premises where there has been a confirmed case.

As the number of cases increases, the measures imposed during the containment phase may become unsustainable. As the virus is reported in more and more locations worldwide, it’s no longer possible to quarantine in government facilities everyone arriving in the country from places where there are confirmed cases. Quarantine is replaced with self-isolation, which of course relies on the compliance of those concerned. Contact tracing may also become impractical as the number of cases increase and there aren’t sufficient resources to trace and follow-up every single person that every person confirmed to have the virus has been in contact with.

With increasing spread of the virus, the closure and deep-cleaning of premises such as schools and healthcare facilities becomes not only impractical, but pointless, because it is likely that when such premises reopen, there will be more confirmed cases. Note that I am talking here about short term closures of a few days while premises are deep-cleaned, not the longer-term closure of places like schools to prevent pupil to pupil spread. More on that later.

Once it is apparent that containment has failed and the virus continues to spread, we enter the delay phase. Now, the aim is to slow the spread of the virus as much as possible. Measures during the delay phase include self-isolation for those who have the virus. Steps may also be taken to prevent or minimise situations where large numbers of people are in close proximity to one another. These may include the closure of schools and colleges; closure of entertainment venues such as cinemas; and the cancellation of large events such as sporting fixtures.

Measures taken during the delay phase will not stop the spread of the virus. So what’s the point? There are three main benefits. To illustrate these, the graph below shows the hypothetical spread of an imaginary virus I am calling X, which is spreading at a similar rate to that seen with COVID-19. The graph shows the number of cases by month, with and without delay measures.

The first benefit of delay measures is that the rate at which the number of cases increases is slower than it would be without. This means that the strain on the NHS would be far less than if there was a very rapid increase. It would also mean that the number of cases at any one time would be lower – again, reducing the strain on the NHS.

A second benefit is that cases would peak later in the year. The weather would (hopefully) be getting warmer, and there would be fewer other pathogens circulating, such as colds and flu. As I discussed in my earlier post, people fighting or recovering from other infections would be more susceptible to complications if they then caught COVID-19.

Thirdly, researchers and health professionals believe, based on the behaviour of other, similar coronaviruses, that COVID-19 will be less able to survive in warmer weather. This means that the time during which the virus can survive outside a host will be much reduced, making it harder for it to spread and potentially reducing the overall number of cases. I stress that at the moment, this last point is hypothetical, but it is a reasonable speculation based on evidence garnered from years of study of similar viruses.

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