As a second wave of infections hits many European countries, the challenge is whether to persist with stringent local measures or go into full lockdown. From an epidemiological perspective the question is raised: assuming full adherence by individuals and organisations to rules on social distancing, masks etc, should that not be enough to suppress the pandemic?
- The key facts are well known I am sure!
- Covid-19 is transmitted from person to person: achieve complete isolation of affected individuals from other human contact and the pandemic can come to an end
- Given the relative contribution of asymptomatic spread, and the total failure of Western democracies to have an effective track and trace system, complete isolation has to apply to the whole population
- The economic and social consequences of complete population lockdown are enormous
- Hence the attempt to achieve the same effect by individual and organisational behaviour change with social distancing, masks and other mitigation measures*
- What does ‘the science’ tell us about how likely it is that such measures would be sufficient ?
*By organisational measures I refer to those undertaken by schools, work places, shops, public transport etc
If proof were needed about human to human spread….
- Rigid enforcement of restricting human to human contact led to the end of the pandemic in Wuhan (Hubei Province)
- More recently the lockdown in Melbourne, Australia, has been similarly remarkably successful
Do we know that perfect adherence to mitigation measures is not equally effective?
- It is a challenge to show either theoretically or in practice that social distancing, wearing of facemasks and hand washing, in combination, are sufficient to reduce either individual risk to zero or the population level to trivial numbers
- I could suggest the perfect epidemiological study:
- Select (say) 20 small relatively self-contained towns
- Undertake baseline surveys to identify at the start those who have, or had evidence of infection by being positive on a swab or antibody test
- Randomly allocate these towns to two groups: (i) lockdown versus (ii) optimal individual and organisational adherence to mitigation actions
- In the non-lockdown group, the research would have to record the actual levels of adherence
- Follow up for (say) 6 weeks
- Compare the rates of positive swabs/antibody tests and clinical cases
- Actually, given the funds that have been used to support the current large scale surveys, and the potential that my suggested approach could prove crucial in understanding the benefits of lockdown, such a study would not be impossible to do or fund!
Any indirect evidence that the mitigation measures in combination may be equally effective as lockdown ?
- The only indirect evidence comes from so called ‘natural experiments’ where the equivalent of the perfect adherence might be assumed
- The best example I believe is Singapore
- Singapore has had around 60,000 cases but with a very high proportion imported from overseas (explaining the spike in summer)
- Well known as a law abiding country, Singapore made mask wearing mandatory in April and issued fines for not keeping to safe distancing
- The data on adherence to mask wearing in public places is compelling, 95% of the population have been reported as wearing masks
Is it that simple?
- Sadly not. The fact that there is a high adherence to these measures in a country with a low and declining rate of infection does not prove cause and effect
- Asian countries in general are doing better than European and American (North and South) in terms of transmission which may be related to background immunity and mutations in the virus
- Singapore is also a very affluent country and overcrowding and poverty in regions with western countries are key contributors to transmission rate
- Given therefore we don’t have a scientific answer to the key question about the value of almost perfect adherence to the mitigation measures, we can look at the scientific evidence about the success of masks and social distancing
How successful could mask wearing be?
- I discussed the data on cloth facemasks in a previous blogpost at the beginning of September:(https://wordpress.com/post/makingsenseofcovid19withs.com/298 )
- I concluded then that “Cloth masks are not the magic bullet to stop an infected person spreading the person, or protect an uninfected wearer from being at risk from others”
- There have now been several epidemiological studies, both in Covid-19 and in other corona virus pandemics, comparing the success of facemasks to prevent transmission. The reduction in rates with facemasks ranged in these studies from 6% to 80%
- Without going into details, the reason for this enormous disparity lies in the ways the different studies were undertaken
- (OK I am defending my epidemiological brethren here!) but these studies are not easy and all kinds of biases can creep in
- One authoritative review from Norway worked on the premise that facemasks probably would reduce the risk by 40%
How successful can social distancing be?
- The challenge in understanding what difference social distancing measures make is based on what we believe to be the relative contributions of droplet and aerosol transmission
- I have discussed this before but worth repeating that initially it was thought that transmission was by large droplets, coughed, sneezed or even just breathed out
- The droplets would fall to the ground fairly quickly, hence the 2 metre rule
- As is now well recognised aerosol (smaller droplet) transmission can occur at distances of up to 8 metres
- Note my use of ‘can’: we just do not know what proportion of cases are being transmitted at this distance
- Again – as I am sure is also well known – ventilation, duration of exposure, how forceful the exposure (eg cough/shout/singing) will all affect the risk
I wanted in this post to provide an understanding of how far individual public and organisational adherence to all the current advice and adoption of the relevant measures to mitigate against transmission could achieve the same success as complete lockdown. The media have all focused on ‘bad behaviour’ but is this the reason for the current surge in Europe?
I guess if this was easily answered then we would have been advised accordingly. I will come ‘off the fence’ though and conclude that even (i) excellent adherence to the face masks that are reasonable for the public to wear and (ii) keeping within a 2 metre distance from non-household members are not sufficient to guarantee (I am guessing at this figure) more than an 80% reduction in personal risk. When the number of cases in the population is rising then these measures are probably therefore not sufficient to bring the transmission down sufficiently (ie bring down ‘R’ below 1) .
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