Asymptomatic infections in SA: five revelations from the MAC report

The Covid-19 ministerial advisory committee (MAC) estimated that the proportion of asymptomatic infected individuals in SA ranges between 50-80%, saying the reasons were not clearly understood.

On Thursday, health minister Zweli Mkhize released some of the advisories from the committee, months after committee members called on the government to release them to the public.

One of the recommendations is regarding asymptomatic infections.

Here are five revelations from the MAC report.

Wide range of estimates

According to an internal memo issued in June, chairperson of the committee Prof Salim Abdool Karim said the wide range of estimates of infected individuals who have an asymptomatic infection was 2% to 85%. 

“Due to differences in study methodology and the types of tests used, there is a wide range of estimates that are 2% to 85% for the percentage of SARS-CoV-2 infected individuals that have an asymptomatic infection.”

Infection rate

Fifty to 80% of individuals infected with SARS-CoV-2 were likely to be asymptomatic, said Abdool Karim.

“Sero-epidemiology studies coupled with the 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 2-3, 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.”

Infected individuals asymptomatic at the time of sampling

“Analysis of an outbreak response in SA indicates that approximately 54% of infected individuals were asymptomatic at the time of sampling,” said Abdool Karim.

“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 common in under 18s

Abdool Karim said asymptomatic infection may be more common in children under 18 than adults.

“The SARS-CoV-2 viral load in asymptomatic infected individuals is slightly lower than in symptomatic Covid-19 cases.”

He said the duration of infectiousness of asymptomatic compared to symptomatic SARS-CoV-2 infected individuals was yet to be fully determined.

“Asymptomatic individuals with SARS-COV-2 can transmit the virus, though are probably slightly less infectious than symptomatic individuals.”