Latest COVID-19 reproductive number falls to just above 1

From stage 5 to stage 3 of lockdown, there has been a decline in the number of new cases, showing a slowing down of COVID-19 transmissions. This can be seen in the latest report of “The initial and daily COVID-19 effective reproductive number in South Africa” where South Africa’s Covid-19 reproductive number (R) is down to 1.1.

The number — commonly known simply as R — is the average number of secondary infections produced by a typical case of an infection in a population where everyone is susceptible. Secondary infections are infections resulting from a single infectious case.

If the reproductive number (R) is more than 1, the number of new cases will increase, such as at the start of an epidemic. Where R is 1, the number of new cases is stable over time, and where R is less than 1, there will be a decline in the number of new cases per time unit. Currently, the reproductive number is down to 1.1 as of 26 July 2020. This indicates that the number of new cases arising from each infectious case has decreased from the start of the pandemic where the reproductive number was at 1.33 and rose to its highest during April to 1.5.

The daily R dropped steadily throughout stage 4 lockdown, with an average over this period of 1.26 continuing to decrease during stage 3 lockdown, with an average of 1.10 from 1 June to 5 July. This indicates ongoing transmission at a steadily slowing rate over this period.

Reasons for the declines in R throughout the stage 3 lockdown may include good public adherence to physical distancing, mask use and other measures, increasing population-level immunity or other factors, including residual biases in the data.

During stage 5 and 4 lockdown, Gauteng, Eastern Cape and KwaZulu-Natal, the R ranged between 1.5 and 1.0. Generally, R showed reductions during stage 3 lockdown indicating a slowing of transmission, however, in KwaZulu-Natal R remained well above 1 indicating increasing infections in this Province.

Read the full report here

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