Younger patients without previous ailments have a much better chance of surviving Covid-19 than elderly patients.
The table below shows the current estimates of the severity of COVID-19 cases. The infection fatality rate (IFR) estimates have been 'adjusted' to account for a 'non-uniform attack rate' giving an overall IFR of 0.9%. Hospitalisation estimates were also adjusted in this way to match expected rates in the oldest age-group (80+ years). These estimates are for the UK and US.
The scientists headed by Professor Neil Ferguson (who has become infected himself and is working from home), from Imperial College and working with colleagues in the US say that these estimates will be updated as more data comes in and gets collated. It is worth noting that Germany are already reporting much lower fatality rates (as of today's date) they have only registered 42 deaths. This compares with France, who have reported 9,058 infections and 243 deaths. Spain had 17,395 infections and 803 deaths. One possible reason suggested for the low fatality rate in Germany is that the infection exists largely in younger people.
So, the modelling forecasts are highly age dependent.
Infection Fatality Rates (IFR) by Age:
|
Age-group (years) |
% symptomatic cases requiring hospitalisation |
% hospitalised cases requiring critical care |
Infection Fatality Ratio |
|
0 to 9 |
0.1% |
5.0% |
0.002% |
|
10 to 19 |
0.3% |
5.0% |
0.006% |
|
20 to 29 |
1.2% |
5.0% |
0.03% |
|
30 to 39 |
3.2% |
5.0% |
0.08% |
|
40 to 49 |
4.9% |
6.3% |
0.15% |
|
50 to 59 |
10.2% |
12.2% |
0.60% |
|
60 to 69 |
16.6% |
27.4% |
2.2% |
|
70 to 79 |
24.3% |
43.2% |
5.1% |
|
80+ |
27.3% |
70.9% |
9.3% |
The full report, Impact of non-pharmaceutical interventions (NPIs) to reduce COVID- 19 mortality and healthcare demand, goes onto describe and model the outcomes from various population infection control strategies or five, so-called non-pharmaceutical intervention scenarios (NPIS). These are as follows:
Infection control strategies |
||
|
CI |
Case isolation in the home |
Symptomatic cases stay at home for 7 days, reducing non- household contacts by 75% for this period. Household contacts remain unchanged. Assume 70% of household comply with the policy. |
|
HQ |
Voluntary home quarantine |
Following identification of a symptomatic case in the household, all household members remain at home for 14 days. Household contact rates double during this quarantine period, contacts in the community reduce by 75%. Assume 50% of household comply with the policy. |
|
SDO |
Social distancing of those over 70 years of age |
Reduce contacts by 50% in workplaces, increase household contacts by 25% and reduce other contacts by 75%. Assume 75% compliance with policy. |
|
SD |
Social distancing of entire population |
All households reduce contact outside household, school or workplace by 75%. School contact rates unchanged, workplace contact rates reduced by 25%. Household contact rates assumed to increase by 25%. |
|
PC |
Closure of schools and universities |
Closure of all schools, 25% of universities remain open. Household contact rates for student families increase by 50% during closure. Contacts in the community increase by 25% during closure. |
Age distribution is already affecting choice of 'suppression' and 'mitigation' strategies
The results from this paper have underpinned both UK and US strategy and predict that school and university closure will have an impact on the epidemic. The key assumption is that children transmit as much as adults, even if they rarely experience severe disease. The effect of school closure naturally helps to break social contacts between families. However, school closure alone will not be sufficient to mitigate an epidemic. This is different to the situation with flu where children are the key drivers of transmission due to adults having higher immunity levels.
In the UK choice of containment strategy will aim at having appropriate measures levelled in order to avoid COVID-19 admissions to ICUs exceeding 200 patients per week.
250,000 deaths forecast for the UK and 1.2M in the US
The research team report that mitigation is unlikely to be feasible without emergency surge capacity limits being exceeded many times over. They go onto stress that, "In the most effective mitigation strategy examined, which leads to a single, relatively short epidemic (case isolation, household quarantine and social distancing of the elderly), the surge limits for both general ward and ICU beds would be exceeded by at least 8-fold under the more optimistic scenario for critical care requirements that we examined. In addition, even if all patients were able to be treated, we predict there would still be in the order of 250,000 deaths in GB, and 1.1-1.2 million in the US."
In this circumstances the scientists conclude that; ".. epidemic suppression is the only viable strategy at the current time. The social and economic effects of the measures which are needed to achieve this policy goal will be profound. Many countries have adopted such measures already, but even those countries at an earlier stage of their epidemic (such as the UK) will need to do so imminently."
