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Government study finds majority of Covid-positive patients were asymptomatic

A large-scale study into Covid-19 infection rates in England has revealed that the majority were asymptomatic when they tested positive.

This was one of a number of findings of a Government-funded trial, led by Imperial College London, which saw 120,000 volunteers from the general population tested to see if they had Covid-19 between 1 May and 1 June. 

The aim was to gain insight into who was infected and comparing geography, age, sex, ethnicity, key worker status and symptoms.

The study also found that people of Asian ethnicity were more likely than those of white ethnicity to test positive for the virus, with the Government commenting that it ‘is possible’ this ‘contributed towards the higher death rates observed in this ethnic group’.

Worryingly, 69% of people testing positive reported no symptoms on the day of the test or the previous week, although the Government said ‘they may have developed symptoms later on and it doesn’t show how infectious they might have been at this time’.

With regards to who was infected, the report showed that:

  • Care home staff and healthcare workers were more likely to be infected during lockdown than the general population;
  • Young adults, aged 18 to 24, were more likely to test positive than other age groups, which the Government said reinforces the ‘need for this age group to adhere to social distancing measures to protect vulnerable friends and family’;
  • There were no ‘significant differences seen between males and females’ and ‘no significant evidence of geographic clustering’ (although measured levels were highest in London and lowest in the South West).

Other key findings included:

  • The rates of infection halved every 8 to 9 days during May, with an overall R number of 0.57 – lower than thought at the time.
  • Anyone who had recent contact with a known Covid-19 case was 24 times more likely to test positive than those with none of these contacts. 

Professor Paul Elliott, FMedSci, director of the programme at Imperial College London, said: ‘Through this surveillance programme with DHSC and Ipsos MORI we’re gathering the critical knowledge base necessary to underpin community testing and facilitate a greater understanding of the prevalence of Covid-19 in every corner of England.’

Health secretary Matt Hancock said: ‘This ambitious testing programme will help us better understand the spread of the virus to date, predict how it may spread in the future and inform our response to the pandemic.

‘It shows the impact our national lockdown efforts have had and demonstrates that we have taken the right actions at the right time. As a country we have made great strides towards beating this virus but we mustn’t take our foot off the pedal, and such studies will be vital as we continue to fight this virus.’

The researchers conducted a similar testing programme during the month of June, including 150,000 volunteers, with a report expected ‘within weeks’.

The news comes as Public Health England (PHE) published a report investigating the disproportionate effect of Covid-19 on people from black, Asian and minority ethnic (BAME) last month, admitting ‘humbling’ health inequalities.

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