Asymptomatic Carriers

In a press conference held at WHO Geneva the first week of June 2020 Dr. Maria Van Kerkhove, head of the WHO’s emerging diseases and zoonosis unit stated that Coronavirus patients without symptoms “aren’t driving the spread of the virus”, casting doubt on concerns by some researchers that the disease could be difficult to contain due to asymptomatic infections. 

Preliminary evidence from the earliest outbreaks indicated that the virus could spread from person-to-person contact, even if the carrier never develops symptoms. But WHO postulated that while asymptomatic spread can occur, it is not the main way it’s being transmitted. 

“From the data we have, it still seems to be rare that an asymptomatic person actually transmits onward to a secondary individual – It’s very rare.”

Since then there is now clearer and stronger evidence that asymptomatic carriers are not the main spreaders of disease especially among children.

In the most recent systematic review undertaken the overall estimate of the proportion of people who become infected with SARS-CoV-2 and remain asymptomatic throughout infection was 15% (95% CI 10 to 22%) with a prediction interval of 3 to 55% in 28 studies that addressed this review question. 

In modelling studies, 40 to 60% of all SARS-CoV-2 infections are the result of transmission from pre-symptomatic individuals, with a smaller contribution from asymptomatic individuals. 

Children do not appear to be super spreaders and no documented evidence has been forthcoming that closing schools has an impact on hospital admissions or infection fatality rates.

It is noteworthy that in the UK Office of National Statistics (ONS) are currently claiming that 33,500 secondary school children currently have a SARS-CoV-2 infection but have not tested positive despite all the school testing. Secondary school children in Scotland are currently being extensively tested. One in 14 secondary school children are currently at home isolating. 6,500 children are self isolating because they tested PCR positive and a further 25,500 are isolating as contacts despite having tested negative. If the ONS were right that 1 in 10 randomly selected children that age would test positive (40,000 children in total) wouldn’t they be easier to find?

If the ONS are right, that means the Lateral Flow Tests are missing 82% of cases, making mass testing utterly pointless.

The other interpretation is that PCR testing, that enables the ONS measurements, continues to have a serious-false positive problem, wildly overestimating the extent of the virus in the country.

From a recent study published in the British Medical Journal on September 2, 2021 found that “Compared with adults of working age who are otherwise similar, teachers and their household members were not found to be at increased risk of hospital admission with covid-19 and were found to be at lower risk of severe covid-19.” – reassuring those who are engaged in face-to-face teaching.


The role of asymptomatic SARS-CoV-2 infections: systematic review. Centre for Evidence Based Medicine, University of Oxford, UK.

Children are not COVID-19 super spreaders: time to go back to school. Archives of Disease in Childhood. BMJ Journals.

Over 30,000 Scottish secondary school children infected but don’t know it Healthy Advisory recovery Team (HART)

Risk of hospital admission with covid-19 among teachers compared with healthcare workers and other adults of working age in Scotland, March 2020 to July 2021: population based case-control study