Professor Salim Abdool Karim, an epidemiologist and infectious disease specialist working with government to fight Covid-19, says this coming week will provide some answers on whether the nationwide lockdown has been effective in curbing the virus. In an interview with News24's Frontline on Wednesday, Karim explained that the state of disaster declared by President Cyril Ramaphosa before the lockdown had helped bring down the number of Covid-19 infections through initiatives like hand washing, social distancing, closing schools and limiting travel.The next week will be critical to determine whether the lockdown has been effective.What makes this coming week so special?Karim explained that, because of the nature of Covid-19, people may not display symptoms for almost two weeks and could be "none the wiser" about their infections. This, coupled with the amount of time it takes to screen and test people, means that results reflect infections that had occurred two weeks earlier.As South Africa enters its third week under lockdown, Karim said this coming week would show a true reflection of cases recorded from the start of the lockdown.This will give a representation of whether these measures have had any impact on the rate of Covid-19 infections, Karim said.This past weekend, 460 000 people were screened for high temperatures and of this group, thousands had been tested for Covid-19, Karim said.This is due to active case finding measures implemented by government where health workers are going out into communities to actively look for Covid-19 cases.As a result, the number of tests have "skyrocketed" and the number of cases now will be higher than previous weeks.How will government measure the effectiveness of the lockdown?Using a statistical tool called the "95% confidence interval" to calculate the number of average cases, Karim said government could determine the success of the lockdown.The tool is based on the average number of cases South Africa records each day in one week. If the daily average is 90 cases or more, it means cases are increasing.If the daily average is within 45 to 89 cases, Karim suggests measuring the number of screenings done against the number of positive results to create a tie breaker.If the average is below 45 then this means infection rates are decreasing.LISTEN | Coronavirus: Has lockdown in SA worked so far? | @Health24com https://t.co/8aSQlXuwlN pic.twitter.com/o5k2b8y96X— News24 (@News24) April 15, 2020Another way to measure this is to simply look at the amount of community transmissions.The purpose of the lockdown is to curb community transmission and, with active case finding, government can measure this to make a call. "I propose a cut-off of one in 1 000. If there is more than one in 1 000 who have this virus, then we should stay in lockdown,” Karim said.He added, however, that the decision to end the lockdown would not just be based on math but a range of social considerations. "The advice that we would give would be based on what the epidemiology is looking like and what the dynamics of the epidemic and the viral transmission looks like."The decision about the lockdown [...] involves many different dimensions. There are social, economic [and] mental health dimensions - there are many different considerations. I don't think there is any simple switch, all of these [factors] need to be considered by wise people," Karim said.