Early results shine new light on COVID-19 infection rates

  • Peter Russell, Medscape.com

  • UK Medical News
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Around 136,000 people in England may be currently infected with SARS-CoV-2, according to first results from a survey into the spread of COVID-19.

The early estimates from the Office for National Statistics (ONS) suggest that around 0.24% of the population had COVID-19 during the period surveyed between 26th April and 8th May.

The ongoing analysis aims to answer some outstanding questions about the pandemic: specifically, how many people have COVID-19, how many people have developed antibodies, as well as providing answers about the rate of community transmission.

Figures so far are based on results of swab tests collected from 7087 individual participants.

The statistics come with some degree of uncertainty about how many people are infected, with the 95% confidence interval put at between 76,000 and 225,000.

The ONS stressed that the estimates, produced in partnership with the University of Oxford, the University of Manchester, research data company IQVIA, the UK Biocentre, and Public Health England, are preliminary and that care needs to be taken when interpreting them.

The pilot survey is currently ramping up to test 10,000 households in England.

Eventually, around 25,000 individuals aged 2 years and over will be involved.

The sample size will be increased over the next 12 months and will take in the rest of the UK.

Testing Over 12 Months

Participants are asked to take tests every week for the first 5 weeks, and monthly for a period of 12 months in total.

Adults from 2000 households will also provide a blood sample taken by a health professional. These tests, the results of which are not yet available, will help determine what proportion of the population has developed antibodies to COVID-19.

The ONS said that the main uncertainties in the data collected up until this month revolve around false positives and false negatives. Also, it is not known whether all people testing positive are still infectious because some may have had COVID-19 in the past but still test positive.

In a statement to the Science Media Centre on Monday, Martin Hibberd, professor of emerging infectious disease at the London School of Hygiene and Tropical Medicine, said the figure of 136,000 current infections "compares with the 3877 identified today from the results of the standard testing, showing new insights about the outbreak."

He said that Prof Patrick Vallance, the Government's chief scientific adviser, had said this week that population-based estimates from the antibody test suggested that approximately 10% of people in London and 4% outside of London may have had the disease by early April.

Prof Hibberd said that "this suggests perhaps 3 million people have had the infection in the UK up to a timestamp of 5 weeks ago".

Prof James Naismith, Director of the Rosalind Franklin Institute, and University of Oxford, commented: "This is a single data point over a long time period, so it is not safe to conclude more. 

"However, in time as more data points from further random sampling are obtained, they will build a picture that will help us understand the spread of virus."

The next regular release of results from the ONS survey will be issued on Thursday 14th May.

Hospital Staff Infection Rates

Doubts over actual infection rates from SARS-CoV-2 in the community persist, with a new study suggesting that 3% of staff in one hospital trust in England tested positive, despite not reporting symptoms.

The results were based on swab tests of 1032 asymptomatic staff at Addenbrooke's Hospital in Cambridge throughout April.

On closer questioning, around 1 in 5 reported no symptoms, 2 in 5 had very mild symptoms that they had dismissed as inconsequential, and a further 2 in 5 reported COVID-19 symptoms that had stopped more than a week before.

The research, mainly funded by Wellcome and the Addenbrooke's Charitable Trust, and published in the journal eLife, demonstrated the need for hospitals to be vigilant and introduce screening programmes across their workforces, the authors from the University of Cambridge said.