Now we’ve been in lockdown for several weeks and it seems as though both the infection and death rates are starting to plateau, thoughts are turning to how do we get out of lockdown and start to return to a more normal existence.
Pandemics end when they run out of people to infect. There are several ways this can happen.
As people fight off the infection they acquire immunity that will help prevent them from becoming infected again, once enough people are immune, the virus cannot find enough people to infect so the pandemic dies out of its own accord, referred to as herd immunity. The very lethal pandemics of the past, Plague, Black Death, Spanish flu, effectively disappeared for long periods this way. This though is not a good survival strategy for the virus as it dies out with its victims, so many less lethal diseases such as Measles, Mumps, Chicken Pox etc, become endemic in the population, infecting people without immunity, mostly babies and children. It is not yet clear whether COVID-19 would self extinguish or become endemic.
This is the Herd Immunity approach which many countries tried before they realised that their health systems would be overwhelmed, risking very high death rates and possible social unrest. Sweden has continued with this approach, encouraging voluntary social distancing and attempting to isolate the most vulnerable, time will tell how successful this approach has been.
In the UK the rapid increase in people requiring hospital treatment and the analysis by Neil Fergusson et al at Imperial College Link here persuaded the government to rapidly switch to a lockdown strategy to prevent the NHS becoming overwhelmed and save lives. A simple calculation would suggest that for the UK, left unchecked the Covid-19 could have caused around 2-300,000 deaths over a short period.
Vaccination works by boosting the number of people immune to the disease by stimulating their immune systems produce antibodies without actually giving them the disease. As with natural immunity once the proportion of immune people becomes high enough the pandemic dies out. For some diseases such as Polio and Smallpox it has been possible to eradicate the disease entirely, had it not been for a fall in vaccination rates it is likely that measles would also have been eliminated from many countries.
It is too soon to tell how easy it will be to create an effective Covit-19 vaccine – it is harder for some viruses than others. For Covid-19 there is some evidence that some people are not carrying antibodies for very long after infection, this may make acquiring sufficient levels of protection in a population difficult, possibly requiring boosters or frequent re-vaccination. Even in the best case the effort required to develop a vaccine, manufacture and give the large number of doses required should not be underestimated so mass vaccination will not be available for many months.
Lockdown, Social Distancing and Isolation
Breaking the population into very small units (households) and isolating them from each other limits the spread of the virus between units and so causes the number of new infections to drop. This has been seen to be effective in China, Italy and Spain. In New Zealand they are close to entirely eliminate Covid-19 this way. In the UK the infection and death rates seem to have levelled out but don’t yet seem to be falling quickly, it is likely that the speed at which a lockdown becomes effective depends on how wide spread the infection was before the lockdown.
The problem with a lockdown is that it is by definition very disruptive both to individuals and the economy and so can only be a temporary measure, the question is how to come out of it.
Unless you can bring the infection rate to zero, vaccinate enough people, or have testing, tracing and quarantine in place, releasing the lockdown is likely to allow the virus to spread again restarting the pandemic, requiring the lockdown to be reintroduced, as has recently happened in Singapore.
Selectively easing the lockdown as several European countries have started to do in the hope that they can balance an improvement in people’s lifestyles and the economy against acceptable infection levels and death rates, raising the difficult ethical question of what are acceptable infection and death rates. Allowing businesses and activities that will boost the economy or that people will appreciate without unnecceasarily increasing the risk would seem to be the key to success.
Testing, Tracing and Quarantine
Less disruptive, but more complex than a lockdown is to test people suspected of being infected, trace everyone they have been in contact with while they were infectious, and persuade all these people to isolate until they either have passed the incubation period recovered from an infection. This method has worked very well in South Korea where they have controlled the outbreak without having a lockdown. It has also been used in Taiwan and is being used to bring China out of lockdown.
The problem with this method is that it requires large amounts of resources to test and trace contacts once there are more than a small number of infected people, however it is the only method that could be implemented in the short term to support the easing of a lockdown.
Using mobile phones to help with tracing contacts has been tried successfully in South Korea but less so in Singapore and other places. The difficulty is in persuading sufficient people to download and use the app and agree to always carry their mobile phones in public. Governments will have to be very transparent about the privacy implications and persuade people that by using the app they are performing a public good.
The likely next steps in the UK likely to be selective easing of the lockdown with more shops and businesses reopening, possibly the reopening of schools and more freedom of movement, coupled with an increase in testing and the use of a contact tracing app. These measures should allow the disease to be controlled while starting to get the economy moving again.
Activities which involve large numbers of people in close proximity, such as bars, cinemas, theatres, air travel and watching sport, as well as travel are likely to remain restricted until infection rates have become very low, either through contact tracing or vaccination.