Some extracts from the Lancet article on #COVID19:
1/Governments will not be able to minimise both deaths from coronavirus disease 2019 (COVID-19) and the economic impact of viral spread. Keeping mortality as low as possible will be the highest priority for individuals;
1/Governments will not be able to minimise both deaths from coronavirus disease 2019 (COVID-19) and the economic impact of viral spread. Keeping mortality as low as possible will be the highest priority for individuals;
2/hence governments must put in place measures to ameliorate the inevitable economic downturn. In our view, COVID-19 has developed into a pandemic, with small chains of transmission in many countries and large chains resulting in extensive spread
3/in a few countries, such as Italy, Iran, South Korea, and Japan.1 Most countries are likely to have spread of COVID-19, at least in the early stages, before any mitigation measures have an impact.
4/What has happened in China shows that quarantine, social distancing, and isolation of infected populations can contain the epidemic. This impact of the COVID-19 response in China is encouraging for the many countries where COVID-19 is beginning to spread.
5/However, it is unclear whether other countries can implement the stringent measures China eventually adopted. Singapore and Hong Kong, both of which had severe acute respiratory syndrome (SARS) epidemics in 2002–03,
6/The course of an epidemic is defined by a series of key factors, some of which are poorly understood at present for COVID-19. The basic reproduction number (R0), which defines the mean number of secondary cases generated by one primary case
7/when the population is largely susceptible to infection,
determines the overall number of people who are likely to be infected, or more precisely the area under the epidemic curve.
determines the overall number of people who are likely to be infected, or more precisely the area under the epidemic curve.
8/For an epidemic to take hold, the value of R0 must be greater than unity in value. A simple calculation gives the fraction likely to be infected without mitigation. This fraction is roughly 1–1/R0. With R0 values for COVID-19 in China around 2·5
9/in the early stages of the epidemic, we calculate that approximately 60% of the population would become infected. This is a very worst-case scenario for a number of reasons. We are uncertain about transmission in children,
10/some communities are remote and unlikely to be exposed, voluntary social distancing by individuals
and communities will have an impact, and mitigation efforts, such as the measures put in place in China,
and communities will have an impact, and mitigation efforts, such as the measures put in place in China,
11/greatly reduce transmission. As an epidemic progresses, the effective reproduction number (R) declines until it falls below unity in value when the epidemic peaks and then decays, either due to the exhaustion of people susceptible to infection or the impact of control measures
12/The speed of the initial spread of the epidemic, its doubling time, or the related serial interval (the mean time it takes for an infected person to pass on the infection to others), and the likely duration of the epidemic are determined
13/ by factors such as the length of time from infection to when a person is infectious to others and the mean duration of infectiousness. For the 2009 influenza A H1N1 pandemic, in most infected people these epidemiological quantities were short
14/the COVID-19 epidemic could be more drawn out than seasonal influenza, which has relevance for its potential economic impact
15/ Third, the effect of seasons on transmission of COVID-19 is unknown; however, with an R0 of 2–3, the warm months of summer in the northern hemisphere might not necessarily reduce transmission below the value of unity as they do for influenza
16/Vaccine development is underway, but the key issues are not if a vaccine can be developed but where phase 3 trials will be done and who will manufacture vaccine at scale.
17/Manufacturing at scale requires 1 or more of the big vaccine manufacturers to take up the challenge & work closely with the biotech companies who are developing vaccine. Process will take time & we are probably @ least 1 y to 18 months away from substantial vaccine production.
18/Social distancing measures reduce the value of the effective reproduction number R. With an early epidemic value of R0 of 2·5, social distancing would have to reduce transmission by about 60% or less
19/School closure, a major pillar of the response to pandemic influenza, is unlikely to be effective given the apparent low rate of infection among children, although data are scarce. Avoiding large gatherings of people will reduce the number of super-spreading events;
20/however, if prolonged contact is required for transmission, measure might only reduce a small proportion of transmissions, broader-scale social distancing is likely to be needed, as was in China. This measure prevents transmission from symptomatic and non-symptomatic cases,
21/hence flattening the epidemic and pushing the peak further into the future. Broader-scale social distancing provides time for the health services to treat cases and increase capacity
22/The key epidemiological issues that determine the impact of social distancing measures are what propor- tion of infected individuals have mild symptoms and whether these individuals will self-isolate and to what effectiveness;
23/how quickly symptomatic individuals take to isolate themselves after the onset of symptoms;
24/ Individual behaviour will be crucial to control the spread of COVID19. Personal, rather than govt action, in western democracies might be the most important issue. Early self-isolation, seeking medical advice remotely unless symptoms are severe, and social distancing are key.
25/If measures are relaxed after a few months to avoid severe economic impact, a further peak is likely to occur in the autumn
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