Asymptomatic cases of Covid-19 account for a high %age of new daily cases in UK

According to a major study published today from Imperial College London, nearly 100,000 people are catching coronavirus every day in England. The report suggests the pace of the epidemic is accelerating fast, and estimates the number of people infected is now doubling every nine days. The authors say we are at a “critical stage” and “something has to change”, as we are fast approaching the peak in infections seen in the spring just before the first national lockdown.

People wear face coverings in Manchester City Centre
There are 96,000 people catching the virus every day according to Imperial College study

This data is at odds with the daily number of cases published by the Gov.Uk dashboard, which today reports the number of new cases at a much reduced figure of nearly 25,000 for the UK. Zoe, the Covid-19 self-reporting app with over 4.3 million contributors puts the number of new cases in the UK at just over 45,500 today with nearly 557,000 active cases in the UK.

In a further report on Friday 30th October, the Office of National Statistics estimated that there were about 52,000 new infections each day in homes in England alone in the week ending 23 October.

So what is going on, and which dataset should we believe ? The React-1 study is highly influential because it is the most up-to-date assessment of Covid-19 in the country, with the last swabs taken only on Sunday, with nearly 86,000 volunteers taking part. The key difference between the daily published figures and the Imperial College case numbers is that their React-1 study randomly tests asymptomatic people to estimate the number of overall new infections. This also goes someway to explaining why the Zoe numbers are lower, in that it also misses asymptomatic people.

So what can we roughly infer from these three data sources ? To me as an armchair analysist, the data can be calculated in two ways :

1 the number of unknown asymptomatic positive cases account for between 50% (from Zoe source) and 75% (from Gov-UK dashboard source) new cases each day. This assumes the daily reported numbers from Gov-uk dashboard and Zoe are included.

2 If all the 96,000 React-1 cases were all asymptomatic and previously unreported, then these should be added to the Gov-dashboard number of 25,000 and the Zoe number of 45,000. This gives a range of 121,000 – 141,000 new positive cases per day, which equates to a range of 68% – 79% of people with covid-19 infected each day are unknown and asymptomatic.

What ever the calculations, this means that for all the daily reported figures from people testing positive for covid-19, there are a there are a further threefold – fourfold of untested people with covid-19 who are unknown, asymptomatic and infectious.

Prevalence of coronavirus infection by region (%). Results based on positive swab results .  .

However, there were glimmers of hope in the report. Cases in the north east of England are still growing, but much more slowly than before. Also the region, along with Yorkshire and the Humber, were starting to see a fall in the number of 18-24 year olds catching the virus, although it is rising in older age groups. This could either mean that Tier 3 restrictions are starting to work, or that a degree of “herd immunity” is being established. click full source

The more worrying trend is that three times as many people aged 55-64 are infected, compared with the previous month’s study, and twice as many over 65s. These groups are the people that will have more severe symptoms of covid-19, who are more likely to require hospitalisation.

A pedestrian wearing PPE (personal protective equipment), of a face mask or covering as a precautionary measure against COVID-19, shelters under an umbrella they are caught in a downpour of rain on Oxford Street in London on June 17, 2020, as lockdown restrictions imposed to stem the spread of the novel coronavirus continue to be relaxed. - Britain's annual inflation rate slid to 0.5 percent in May, the lowest level in four years, as the country's coronavirus lockdown dampens prices, official da
Stricter measures need to come into force, according to experts

Although France and Germany have turned to forms of lockdown, albeit not as severe as those endured earlier in the year, the UK government is sticking to its regional strategy. Rather than a national lockdown, the key strategy that that the government could implement would be “focussed protection” of the elderly and clinically vulnerable – ie the re-introduction of “Shielding” this vulnerable group to both protect the NHS from being over-run, and developing herd immunity in the younger population.

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