It was the Brexit campaign that brought the term “Project Fear” into common currency, but some may well feel that Brexit was only a warm-up exercise for the “Great Covid Fear” that now stalks the news media, and by extension the nation, and indeed seemingly the whole world.

The “We are All Going to Die!” hyperbole might normally be regarded as a hysterical over-reaction to a coronavirus with a well documented survival rate well above 99% for the vast majority of those infected, but it seems to have inexplicably been taken at face value by governments and the pharmaceutical industry alike in a headlong rush to panic the entire populace into accepting, nay demanding, vaccines which a leading expert has described as experimental.

Recently indeed we have seen many full-page advertisements in the British press, national and local, which feature the claim (above a disturbing image of a person in an oxygen mask) that:

Around 1 in 3 people who have Covid-19 have no symptoms and are spreading it without knowing

Really? Doesn’t seem at first glance as at all likely. But then it probably doesn’t matter as it will likely evoke an emotional response big enough to swamp any unease about actual veracity.

Let’s set aside the emotion and examine this claim dispassionately.

Covid-19 is the disease caused by SARS-Cov-2 the virus. So let’s nit-pick for a moment. It is possible to have the virus without symptoms, but if we accept that to be described as diseased we must have some symptoms, then this statement falls at the first hurdle. We cannot both have the disease and be asymptomatic. 

Nevertheless, let us be generous and examine an alternative statement:

Around 1 in 3 people infected by SARS-Cov-2 have no symptoms and are spreading it without knowing

It must be reasonable to assume that they have identified these people who didn’t know they had SARS-Cov-2 from the widespread testing of people in the general population, using the RT-PCR test, sometimes referred to as the “gold standard” of tests for SARS-Cov-2. This is anyway the only test in widespread use in the UK (or anywhere else for all I know).

How accurate is this test for SARS-Cov-2?

The WHO has recently published a note reminding us that this RT-PCR test is liable to produce a significant proportion of false positive results when applied in a population with a low prevalence of the virus. The general population at large undoubtedly has a very low prevalence overall when compared with any other likely sample. Therefore it is perfectly reasonable to expect that the number of false positives returned by this test is a not insignificant proportion of all the positive results. The exact proportion remains obscure.

This significant proportion of false positives (it must be significant for the WHO to draw attention to the resulting inaccuracy) arises because this test is designed to detect fragments of DNA/RNA which may come from the virus, or which may occur naturally either from dead particles of infected cells, incomplete viral particles or other sources. It does not necessarily imply that the person is infected with significant quantities of the intact virus. They may in fact have no intact virus at all.

The assumption that a “case” identified by the test is always a real live infection is fundamentally flawed.

Now let us consider the evidence for asymptomatic propagation of the virus

JAMA is the most widely circulated general medical journal in the world“. The JAMA Network published an analysis of 54 studies with 77,758 participants, which concluded that the estimated overall “household secondary attack rate” was 16.6% – but that included all positive individuals both symptomatic and asymptomatic. 

Correcting for the presence of symptomatic cases, the secondary attack rate for asymptomatic infections was estimated to be much lower at only 0.7%, with an upper bound (with 95% confidence) below 5%.

(Now it is true that the paper does not consider “non-household” secondary attacks, so for our purposes there is a degree of error here, but we might reasonably guess that “non-household” would be lower than the “household” secondary attack rate since infected people would have been isolating.)

So in conclusion, if the test is flagging up more cases than really exist, and if the alleged asymptomatic onward transmission occurs in less than 5% of the real asymptomatic viral infections, then ask yourself:

a) Could the government’s statement be true?

We don’t know the percentage of those infected that had no symptoms. But if the “worst case” upper bound 5% of the asymptomatic infected are spreading it in line with the JAMA study, then even if all 100% of those with positive tests were asymptomatic (work with me here) there could not be more than 5% of that total spreading it (and obviously there will likely be much less in reality), so “1 in 3” must be regarded as out by rather more than a factor of 6. 

To put this into some sort of estimated perspective, if we make some relatively conservative assumptions that 30% of the positives are false and 60% of the remainder are asymptomatic and that 2% of the infected asymptomatic do actually transmit the infection then we arrive at a factor of 

70% x 60% x 2% = 0.84%  or around 1 in 120 “cases”  (positive results taken as valid infections)

or 60% x 2% = 1.2% or around 1 in 83 (if false positives are not taken as valid infections).

So there we have it – “1 in 3” who have the virus, and are asymptomatic, and are spreading it does indeed seem well out of court.

b) Does the advertisement give a fair impression of the alleged danger?

I will leave this as an exercise for the reader.

c) Footnote

The Advertising Standards Authority (ASA) has already upheld at least one complaint about our Government’s Covid advertising.

 

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