Covid: R value and the meaning for UK’s lockdown

R value is the most important parameter to know the real spread of the covid and has direct consequences on lockdown.

Before the lockdown measured is lifted, the government has set five key tests. Key to understanding this is a number known as the ‘R’ value or the “effective reproductive number”. Boris Johnson has said reducing the R number of Covid spreading is our “collective endeavor”, and the UK’s top epidemiologists will be continually trying to calculate it as the government mulls easing measures.

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Covid: what is R value

Now we should know about R deeply. The R number is a measure of the extent to which a disease is spreading throughout the population. Put simply, it is the calculation of how many people an infected person is thought to transmit the virus to on average. If the R value is one, each carrier passes the virus on to one other person, meaning the prevalence of the virus will remain at the same level, or if it falls below one start to diminish.

However, if the R is two, each infected person will transmit the virus to another two people. Even if the R is only slightly above one, the virus will continue to spread exponentially.

Epidemiologists reveal that estimations of R are imperfect and are forever being revised. In early March, the World Health Organisation placed the R for the Covid-19 between 2 and 2.5, in the setting of a population with no immunity or social distancing measures. There are many different ways of calculating R, with much of the mathematics reliant upon educated guesses and often extremely variable estimates. The chief scientific adviser Sir Patrick Vallance has previously said UK scientists are looking at all sorts of things including contacts, looking at genomics, looking at data from ambulances, hospital admissions, and so on.

Now the UK is seeking to significantly ramp up its strategy of “test, track, and trace”, which will likely help epidemiologists in their bid to monitor the country’s reproductive number as accurately as possible. Governments across the world have said the R needs to be considerably below one for lockdown measures to be eased in any significant fashion. On 7 May, Dominic Raab paved the way for the prime minister to announce the slight easing of some restrictions, he suggested the current estimates placed R between 0.5 and 0.9. However, England’s chief statistician Professor Ian Diamond said moments later that he believed R was actually rising, mainly as a result of transmissions in care homes.