This is the first of a re-run of our Transmission Riddle series, which was originally posted in 2022. Each post has been updated and reworked with what new evidence we could find. The serial numbers of the original posts may not correspond as we expand, merge, edit and add, like a concertina. 

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Fascinated by the explosive nature of the transmission of SARS-CoV-2 in Lombardy and nearby Veneto (Italy) in the late winter of 2020, we discussed what circumstances may favour the rapid spread of an agent. 

In our post on Covid and Death: Part 1 - The Exponential Phase, we pointed out that infection onset precedes symptoms by a few days and succeeds diagnosis and reporting by weeks, so symptom onset is the closest approximation to infection date. However, there are several unknowns: we need to find out if this is the case for everyone, what the time lag is and what this means in the context of asymptomatic infections. The research developed during the pandemic has been low quality, largely assumption-based and forms part of the poor quality modelling that has remained unreliable.  

Credit: Istituto Superiore di Sanità (ISS), Italy

For example, this statement from the CDC: “Compared with flu, COVID-19 can cause more severe illness in some people. Compared to people with flu, people infected with COVID-19 may take longer to show symptoms and may be contagious for longer periods of time.” On what evidence is this based?

Here’s what they report

“Flu: Typically, a person may experience symptoms anywhere from one to four days after infection.” 

“COVID-19: Typically, a person may experience symptoms anywhere from two to five days up to 14 days after infection.”

Putting aside what the F word refers to, a review of published studies of volunteers challenged with wild-type influenza virus showed that viral shedding increased sharply between 0.5 and 1 day after the challenge. Symptomatic infection occurred in two-thirds of the challenged volunteers. The total symptom scores increased on day one, peaked on day three and returned to baseline by day 8.  

Our work on the duration of symptoms of respiratory tract infections in children shows that the duration of symptoms is much longer. One in ten children still have an acute cough at 25 days. 

So, yet again, we’re left with authoritarian advice that isn’t backed up by the evidence. It is not the first time we have come across the problem of evidence-free assertions. In 2020, we did not realise that “cases” were defined as PCR positivity alone (or other tests) in symptomatic people without any reference to viral load or the properties of the tests. 

Therefore, we asked those responsible for pandemic management in Lombardy to test for the presence of other agents, which could partly explain the spread and seeming lethality of SARS-CoV-2. Unfortunately, because of political interference, our requests fell on deaf ears; we will probably never know what else was circulating at the time. 

The unfolding narrative reported a sharp decline of other viral pathogens once SARS-CoV-2 started doing the rounds. Several other countries reported the crash in other respiratory agents. Scientific American considered Flu Disappeared for More Than a Year, and The New York  Times considered The Flu Vanished During Covid. And asked, What Will Its Return Look Like?

Credit. Flu Has Disappeared for More Than a Year. Katie Peek April 29, 2021. Scientific American 

We assume here that the F Word is synonymous with influenza A and B.

This narrative that influenza disappeared continues to the present day: “During the coronavirus disease 2019 (COVID-19) pandemic, the influenza virus had a very low prevalence, and in many areas, outbreaks were almost non-existent.”

But is this true?

These findings could be due to ascertainment bias: test for SARS-CoV-2, and you shall find it, never mind the other agents.

Multiple respiratory viruses can concurrently infect an individual. Initial infection can enhance or reduce the replication of a second virus. Such viral interference may confer a temporary nonspecific immunity. So, an increase in one virus may lead to a reduction in another.  

One virus that didn't seem to go away was the good old rhino. It is known that influenza and rhinoviruses compete, and RSV can trump rhinoviruses.

However, our knowledge of how viruses compete is very limited. These phenomena made us curious about how the agent spread, a topic which had engaged generations of previous micro-epidemiologists since the 1918 Spanish influenza pandemic. 

Experiments and careful repeated observations of previously known agents conveniently corralled into the label “common cold”, such as rhinovirus and coronavirus, indicate a mixed transmission mode with no specific main pathway. For example, rhinovirus spread through contact and fomites during a famous experiment simulating a poker game with extensive cross-contamination of playing cards. By the way, those of you sniffing the whiff of history in all this will not be disappointed; bear with us through the series.

A 2018 scholarly review pre-dating the SARS-CoV-2 psychosis indicated that the evidence of the mode of transmission of the primary respiratory viruses was mixed (droplets, contact, fomites, aerosol) and probably depended on the situation.

During the covid pandemic, such scholarly careful work was overtaken and ignored by strident statements of certainty that do not fit with the preceding century of detailed research.

By the end of 2022, over  6.5 billion SARs-CoV-2  tests were done worldwide, pretty close to a test for everyone on the planet if you count all discarded. The US had done over a billion, the highest of any country; the UK, half a billion. Such use, on an industrial scale, is unprecedented and has helped distort perceptions, as we shall discuss in subsequent posts.

In addition, SARs-COV-2 has become the most studied agent of all time. Litcovid is the most comprehensive resource on the subject, providing access to 394,017 (and growing ) PubMed articles. The media also went overboard: Covid accounted for roughly a quarter of all front-page online news articles between January and October 2020. 

So,  nearly four years on, what have we learned?