Source: United Kingdom – Science Media Centre
It has been reported that a record 33,470 people have tested positive for coronavirus in the UK government’s latest daily figure.
Prof Liam Smeeth, Professor of Clinical Epidemiology, London School of Hygiene and Tropical Medicine, said:
“Given what we know about the incubation period of Covid-19, which is the time from someone getting infected until their symptoms start, I am not surprised or too dismayed by this figure. The median incubation period is around 5 days, it is then likely to take people a day or so to get tested. In addition the data refer to the number of positive tests reported today, so again there will be some delay from when the tests were actually done. This all suggests high levels of infection around 7-10 days ago, around the time when stricter measures were put in place. We know viral transmission was increasing in many parts of the country at that time – hence the need for the stricter measures. Some of the increase in cases will be due to the welcome increase in the numbers of people getting a test, rather than reflecting a true increase in infections.
“The next few days will be crucial, and my hope is we will start to see a reduction in the number of cases. The reduction may be quite gradual, and if the numbers tested continue to rise the observed reduction in cases may not be as dramatic as we might like to see. However, it is very likely the current stricter measures to reduce spread will begin to feed through into the number of cases we are seeing. Let’s all hope so.”
Prof Deborah Dunn-Walters, Immunology Section Lead, University of Surrey, said:
“This number will include the data from the mass testing in Liverpool using the lateral flow devices. I suspect that what we are seeing are some of the asymptomatic cases that were previously hidden to us when we only tested people with symptoms. It would be interesting to see what proportion of the cases were asymptomatic.”
Prof Igor Rudan, Joint Director of the Centre for Global Health and WHO Collaborating Centre, University of Edinburgh, said:
“The new spike in the UK coincides with a massive recent spike in the USA, where a daily maximum of nearly 143,000 has been recorded yesterday. However, in the UK we should not be too concerned over single-day numbers, because they may vary a lot and reflect behaviours from several days earlier. Those behaviours may have been atypical and unlikely to be repeated. It is better to look at 7-day averages and compare their trends.
“Also, we know from the REACT study that many new infections in the population were not confirmed through testing. The recent increase in daily testing capacity will contribute to an extent to an overall rise in the number of new cases who tested positive. Then, even after lockdown, the virus can still spread within households and affect several more household members. This is why the effect of a lockdown on the rise in the number of cases is not immediate. However, with all the measures of social distancing currently in place, it is unlikely that this growth would persist.
“If the growth does persist, this would represent a peculiar finding. However, even such findings are possible. This is because viruses have complex transmission dynamics. For the novel coronavirus, it has been shown that it largely depends on people’s behaviour and movement. However, it is likely that it can also be affected by factors that we do not fully understand and cannot easily control. It is known that respiratory viruses can have seasonal peaks in various climates, where wet and dry seasons affect the outbursts in their transmission. Then, the large changes in the proportion of time spent indoors or outdoors can also fuel the waves of epidemics.
“Viruses can move between species during different parts of the year and prefer one “reservoir” over the other, only to return to the initial one again. Also, it is increasingly clear that the speed of spread of SARS-CoV-2 can be accelerated by so-called super-spreading events, where a small number of those already infected will affect a larger number of newly infected. This is why any large social gatherings that occur in sequence may lead to large outbursts and overwhelm the health system. This is why a given set of preventative measures may work well at one point in time to keep the epidemic under control but require strengthening at another to prevent it from growing exponentially.”
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