Preamble: I wrote this post for another site that was considering myth-busting type posts, which is why it’s written in the third person. However, the myth-busting part of the site never really took off, so I thought I would post it here. There’s no specific reason to do so now. It just seemed unfortunate to waste a post and it allows me to not think about writing another post for a while.
There have been some who have argued that lockdowns don’t work, or that they’re not effective. Here we want to clarify the current understanding of the impact of lockdowns. One issue is that the term lockdown hasn’t always been well-defined. We define it as a set of restrictions that substantially reduces contact between individuals who are not in the same household.
It is very well understood that viruses mostly spread through people coming into close contact with others. The spread could be through direct contact with another person, touching something that has been touched by someone else, or through aerosol transmission. Consequently, restrictions that limit contact between people will also limit the spread of the virus. The stricter the restrictions, the more they will do so.
Consequently, if we implement restrictions that we might describe as a lockdown (stay at home apart from essential travel and some exercise) then we would expect this to substantially reduce the spread of the virus. Not only is this consistent with our basic understanding of virus transmission, there are also plenty of studies that indicate that this is indeed the case.
An issue, though, is that a very effective lockdown that brings down the number of cases and limits the spread of the virus, will leave a large fraction of the population still susceptible. Hence, if the restrictions are then lifted while the virus is still circulating in the community, the infection can start spreading again, cases can start rising again, and limiting this would then require implementing new restrictions.
So, the issue isn’t so much the lockdown itself, but what we do to avoid cases rising again when we exit the lockdown. Consequently, public health experts would argue that lockdown-like restrictions should be used to bring cases down to the point where we can then implement alternative interventions, such as effective border controls, and test, trace and isolate, to control the spread of the virus in the community once the lockdown restrictions have been relaxed.
Of course, it may be possible to control the spread of the virus without initially implementing lockdown-like restrictions. However, for a highly transmissible virus this would require acting while case numbers are still low so that these alternatives can be effective. Any delay means that more stringent restrictions would then need to be implemented.
Also, during the early stages of an epidemic, cases increase exponentially; in the UK cases were doubling every 3-4 days in early March 2020. Consequently, if less stringent interventions are implemented and they aren’t effective, cases will continue to rise, as will the number of deaths and the incidence of long-term illnesses.
So, there is a very short period of time over which we can attempt to control the spread of the virus using interventions that are less stringent than a lockdown. If these don’t work effectively, then we will have missed an opportunity to limit the number of cases, and deaths, and may have to implement lockdown-like restrictions anyway.
This can also lead to the somewhat counter-intuitive result that the outcome in countries that implemented very strict, lockdown-like restrictions can be worse than in countries that implemented less stringent restrictions. However, this is because stricter interventions become necessary if the initial interventions had little effect, or if there is a delay to the implementation of restrictions.
Hence, it’s not lockdowns themselves that cause the outcome to be worse, it’s that regions that have failed to act appropriately at an early stage of the epidemic need to then implement much stricter interventions than those regions that took effective action at an early stage of the epidemic. Taking decisive action early can limit the spread of the virus without having to implement lockdown-like restrictions, or can do so with shorter, more focussed, lockdowns.
The motivation here is not to debate whether or not lockdowns are good, or bad, but to simply highlight that lockdown-like restrictions clearly have an impact on the spread of the virus. We also want to stress that the implementation of lockdown-like restrictions, and how invasive they are, depends on how promptly action has been taken to limit the spread of the virus. More stringent restrictions will tend to be associated with worse outcomes because of delays in implementing effective interventions, not because these stringent restrictions led to these worse outcomes.