Effects of interventions
A large team at Imperial College London, under Neil Ferguson, is reporting regularly. A report on 30th March[xii] uses mathematical modelling to make estimates about the effects across European countries. It says
“only a small minority of individuals in each country have been infected, with an attack rate on average of 4.9% [1.9%-11%] with considerable variation between countries. Our estimates imply that the populations in Europe are not close to herd immunity (~50-75%). The rate of acquisition of herd immunity will slow down rapidly. This implies that the virus will be able to spread rapidly should interventions be lifted”.
It appears that the interventions to suppress the epidemic (social distancing etc. are proving effective:
“We estimate that ..interventions have had a substantial impact …in countries where there has been time to observe effects (Italy, Spain)”
In “Italy …despite mounting pressure on health systems, interventions have averted a health care catastrophe where the number of new deaths would have been 3.7 times higher”.
“We cannot say for certain that the current measures have controlled the epidemic in Europe; however, if current trends continue, there is reason for optimism”
This suggests to me that the restrictions are working, so it looks likely that the daily death toll will reach a peak within a few weeks in Europe. People will continue to die, of course, but the daily numbers will gradually reduce. However, as few people will have had the disease and no vaccine is yet available, very few will be immune (around 5%). So as soon as we start mixing again the infection rate could pick up. It seems to me this means restrictions will be with us for a long time and will only be lifted in carefully calculated stages.
“Herd” immunity
As the number of people who have become immune grows, so the chances of you being in contact with an infected person decreases. As a result, you are statistically less likely to get infected (though some still will of course). The phrase “herd immunity” is used to describe the condition when sufficient individuals have become immune to protect the whole community. Official sources in Germany and the UK estimate that 60–70% of the population will become infected before this can be achieved. These diagrams (courtesy of Tkarcher on wikipedia) show what happens as immunity develops across the population:
It’s impossible to predict the peak and ultimate duration of the outbreak. It may differ in different places. According to the Imperial College study led by Professor Neil Ferguson[xiii], social distancing and other measures would “need to be in place for many months, perhaps until a vaccine becomes available” (potentially a year to eighteen 18 months). Thereafter, returning to conditions before the pandemic may be gradual. As researchers at the Johns Hopkins University say “we will have to take a step-wise approach toward letting up on these measures and see how things go”.
Enforcement and compliance
Psychologists and social scientists research the behaviour of populations when they are asked to make changes. Below are summaries from two organisations aimed at the general reader:
The Oxford Research Encyclopedia of Psychology from Oxford University Press offers a summary of “principles of influence”, based on what it describes as “a vast body of scientific evidence”. These “generate compliance in the widest range of circumstances”.
Reciprocation: people are more willing to comply with requests (for favours, services, information etc.) from those who have provided such things first.
Commitment/Consistency: people are more willing to be moved in a particular direction if they see it as consistent with an existing commitment.
Authority: people are more willing to follow the directions or recommendations of a communicator to whom they attribute relevant expertise.
Social Proof: people are more willing to take a recommended action if they see evidence that many others, especially similar others, are taking it.
Scarcity: people find objects and opportunities more attractive to the degree that they are scarce, rare, or dwindling in availability.
Liking: people prefer to say yes to those they like, such as those who are similar to them and who have complimented them.
A knowledge sharing platform called Preventionweb is run by the UN Office for Disaster Risk Reduction[xiv]. It offers this from the Jerusalem Center For Public Affairs (JCPA):
“Just as people continue to smoke, to consume sugary drinks, refuse to exercise, and even reject required medication, so will people test the boundaries of government instructions, and many will simply refuse to comply.”
The website offers this list of categories:
Refusers: people who are either oppositional in their attitude or in denial regarding the effects of their refusal.
Deniers: whose personality and social identity is central to their daily functioning. Their adjustment may require more time and may be accompanied by attempts to minimize the seriousness of the need to distance or to challenge it by erroneously claiming the need to continue life as normal in the face of a threat.
The Young: one review of low adherence in adolescents noted, “… they may remain self-centred and feel invulnerable to consequences – negative things happen only to others.” The under-21 population will be difficult to control, especially since they realize that the danger the virus poses to themselves is minimal.
Cultural, Religious, Tribal factors: group dynamics can create patterns of behaviour that are reinforced by peer pressure and embedded in collective behaviour. While official and responsible religious leaders have …urged complete compliance, we can expect .. certain sectors and outliers within the community to have difficulty breaking from traditional practice and routine.
It goes on to advise:
- Frequent reminders in the media and repetition of key points (handwashing, 2-meter rule, etc.) will improve compliance.
- Classifying the refusers’ behaviour as a risk and treating them as a genuine threat is a national priority
- When peers make known their displeasure and disapproval of not following guidelines, noncompliance is likely to fall.
- Since the cadre of those who intentionally or unintentionally put the public at risk cannot be eliminated solely through education and social pressure, law enforcement and government authorities may have to intervene.
Personal level of risk
It’s not easy to judge your personal level of risk. The respected Winton Centre for Risk and Evidence Communication at the University of Cambridge has produced a detailed chart showing what the risks are statistically for people of different ages and gender[xi]. It’s a bit complicated but shows, for example, that a 77 year old male has a 4% risk of dying during the year anyway and now, with COVID -19 included, the risk rises by just one percentage point, to 5% – a smaller effect than you might think.
Amount of virus
At the moment it seems unclear whether the amount of virus an infected person is carrying shows how severe the infection will be. Research in Lombardy found no difference in ‘viral load’ (the concentration of virus in a sample from the body) between those with symptoms and those without. Similarly, in a hospital in Guangzhou no obvious difference in viral load was found between milder cases and those who developed more severe symptoms. But a study in Nanchang found a strong association between disease severity and the amount of virus present in the nose. So, it’s too early to be definitive on the basis of research. On a practical note, however, a person with mild symptoms may have plenty of virus in their throat, if not in their lungs, so their cough can infect another who could become more seriously ill.
This is what I have managed to glean, as a non-specialist. Any further information or corrections you can offer would be welcomed. Andrew Morris
Sources
[xi] https://medium.com/wintoncentre/how-much-normal-risk-does-covid-represent-4539118e1196
[xii] https://www.imperial.ac.uk/media/imperial-college/medicine/sph/ide/gida-fellowships/Imperial-College-COVID19-Europe-estimates-and-NPI-impact-30-03-2020.pdf
xiii https://www.imperial.ac.uk/news/196234/covid19-imperial-researchers-model-likely-impact/
Getting to Grips with Science 