How R rate data lags could mean lockdown is extended

THE R rate is one of the key metrics used to guide public policy on the coronavirus pandemic, including whether to go into lockdown. However, the data used by Government scientists to determine the estimated weekly figure has a time delay of up to three weeks, experts have warned.

It means that it could be the end of the month before a national lockdown starts to show any impact on the crucial figure.

The R value is the number of people an infected person will transmit the disease to and is based on estimates, shown as a range.

On Friday, October 30, the Scientific Advisory Group for Emergencies (Sage) estimated the UK’s R rate to be between 1.1 and 1.3.

Separate research by Imperial College London, published on Thursday, October 29, suggested the value could be much higher, at almost 3 in London and above 2 in the South.

On Saturday, October 31, Boris Johnson explained the country will go back under strict measures for four weeks after local restrictions failed to sufficiently reduce infections.

However, there was some suggestion it could be extended beyond December 2 after Cabinet Office Minister Michael Gove admitted they may need to be in place for longer.

Sage says it uses several models, each using data from a variety of sources, but warned that means there is a time delay on their estimates.

“Epidemiological data, such as hospital admissions, ICU admissions and deaths, usually takes up to three weeks to reflect changes in the spread of disease,” they said.

“This is due to the time delay between initial infection, having symptoms and the need for hospital care.”

Sage also uses household infection surveys, where swabs are performed on individuals – which can provide estimates of how many people are infected.

Professor Neil Ferguson, whose modelling prompted the first lockdown in March, said it will take “probably two to three weeks” to see whether another shutdown will lead to a reduction in hospital admissions.

“If People reduce their contacts as we expect them to, then that will be immediate, but it takes time for it to filter through into reduced admissions to hospitals, reduced deaths per day.

“That will take time, so it will take us probably two to three weeks to see an effect on numbers.”

Asked if it would be helpful for schools to close, Prof Ferguson, of Imperial College London, said, “From a purely epidemiological perspective, getting the transmission down, clearly it would, it would reduce transmission.

“But you have to counter-balance that with the harms closing schools do, and that fundamentally is why we have politicians making those judgements.”