The latest Covid-19 “R number” is hovering around 1.5, the National Institute of Communicable Diseases (NICD) said on Friday.

This means every infected person is passing on the virus to around 1.5 people, so the number of new cases is increasing.

In the four provinces where there are enough cases to calculate an R number, the Western Cape's is the highest, on average.

The NICD analysis, which comes with several caveats, says the five weeks of level 5 lockdown which began on March 26 “substantially reduced the national R, likely contributing to substantially slowing the progression of the epidemic”.

But the fact that R remained above 1 meant transmission of Covid-19 was continuing, and “further easing of lockdown restrictions may be associated with increases in R in different provinces as contacts between people increase”.

The NICD report covers the period from SA's first confirmed infection on March 5 to May 19. The final date, however, allowed 14 days for testing delays and development of symptoms, meaning it takes account of infections that happened up to May 5.

SA's initial R, calculated on March 24 and based mainly on transmission of Covid-19 from international travellers arriving in SA, was estimated between 1.7 and 2.5.

The NICD said changes in the rate of reporting Covid-19 cases and definitions for testing would affect estimates of R.

“While we attempted to adjust for changes in testing practice, residual bias may remain,” they said.

“Therefore, it is important to interpret these findings together with data on testing and other sources of data on transmission.

“In addition, caution should be exercised in interpreting comparisons between different time points and provinces as these could be affected by different testing practices.”