The COVID-19 Ministerial Advisory Committee (MAC) estimated that the proportion of asymptomatic infected individuals in South Africa ranges between 50-80%, saying the reasons were not clearly understood.
They said in an answer to the question:
What proportion of individuals infected with SARS-CoV-2 are expected to be asymptomatic, and what should the strategy be for dealing with asymptomatic infections?
Due to differences in study methodology and the types of tests used, there are a wide range of estimates (2% to 85%) for the percentage of SARS-CoV-2 infected individuals that have an asymptomatic infection.
• Sero-epidemiology studies coupled with history of past illness consistent with possible COVID-19, and cross-sectional sampling for identification of active infections (particularly in pregnant women at time of labour, as well as, in outbreak responses), coalesce around an estimate of 50-80% of individuals infected with SARS-CoV-2 that are likely to be asymptomatic.
• Analysis of an outbreak response in South Africa indicate that approximately 54% of infected individuals were in asymptomatic at the time of sampling. This included outbreaks in prisons and shops. Systematic follow-up of these cases is limited, hence, impeding an evaluation as to whether these cases may have been in a pre-symptomatic phase, rather than being asymptomatic.
• Asymptomatic infection may be more common in children (The duration of infectiousness of asymptomatic compared to symptomatic SARS-CoV-2 infected individuals remains to be fully characterised.
• Asymptomatic individuals with SARS-COV-2 can transmit the virus, although are probably slightly less infectious than symptomatic individuals.
Their recommendations are: While the proportion of asymptomatic infected individuals is still not clearly understood, it is estimated to range between 50-80%.
• Close contacts of individuals with confirmed COVID-19, whether symptomatic or asymptomatic, should be in self-quarantine as per the recommendations.
• Transmission of virus by asymptomatic infected individuals can be reduced by the promotion of adherence to the same non-pharmaceutical interventions recommended for symptomatic individuals.
• Messaging on SARS-CoV-2 infection, should include mention of asymptomatic infection where appropriate.
[link url="https://sacoronavirus.co.za/wp-content/uploads/2020/08/MAC-Memo-Asymptomatic-Infections-18-June-2020.pdf"]COVID-19 Ministerial Advisory Committee (MAC) advisory[/link]