Dr Peter English answers some of the questions about Covid-19 you might still have about the pandemic that stopped the world 10 months on.


First published in December 2020.


I blogged back in April about some of the questions about Covid-19 that I expected science to find answers to.

Some of them have been answered. There is fairly clear evidence, for example, that people are not infectious beyond 9 or 10 days after the onset of symptoms.[1] Viral RNA can be detected for variable lengths of time; but not viable, potentially infectious virus. And the value of masks in preventing transmission is pretty much undeniable now.

Fomite and airborne spread

We know a bit more about the key modes of transmission. I blogged recently about what we now know about airborne transmission, and the importance of ventilation. But – perhaps I have missed the studies – I still know relatively little about fomite transmission. My strong suspicion from what I have read is that the virus is viable for at most a few hours – and quite likely only an hour or two – on most surfaces. So all these schools and other places who are using “fogging” and “deep cleaning” are probably missing the point. If you can catch the infection from touching surfaces (and then touching your eyes, nose, or mouth), then it’s probably only from a surface that has recently been touched by a case who has recently touched their mouth or nose, or coughed on their hand... But I’m not sure I’ve seen any papers confirming this.

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We still know relatively little about fomite transmission.

Antibody levels and immunity

And another really important thing relates to practical immunity. I’m pretty sure that we must, by now, have a pretty good understanding of the types and levels of antibodies that indicate immunity, and of the rates of decay of these antibody levels. That, if somebody has neutralising antibodies above a certain titre, they can (for all practical purposes) be considered immune; and that we should be able to predict, from knowing how quickly antibody levels can fall, how long this immunity can be relied upon (at the end of which period another blood test might indicate whether the antibody levels are still above the protective threshold).

Testing – reliability

I’ve blogged quite a lot about tests (e.g. on sensitivity, in June) More tests have come online: Lamp tests (a beefed up form of PCR testing) and antibody testing (real antibody testing, not the earlier misnomer!).

Mass population testing has been rolled out (despite the fact that it is clearly screening, and it does not meet the criteria for screening) in parts of the UK.

We have not yet seen evidence of the real-world accuracy (sensitivity, specificity, predictive values…) of such tests.[2] “Test and release” concepts – in which people who test negative for the virus can be permitted to do things that would risk spreading the infection if they were infectious (attend concerts, travel on public transport, fly on aircraft, work without a mask...) – will only work if the negative predictive value of the test is very high. I am not confident that sufficiently sensitive tests exist yet (although immunity testing, as I suggest above, might work for this).

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Testing is too unreliable. Too many false negatives, and too short a time from infection to infectiousness.

Test and trace

A huge amount has been said about test and trace – or test, trace, isolate, support; or even FETTISH – with breathless commentary about how we are not doing it right or successfully.

I have become increasingly skeptical of the potential value of such systems. Quite apart from the huge overvaluing of the testing aspect (if you await the test result, it’s probably too late to take effective action; and are tests sensitive enough to safely release people and their contacts from self-isolation)?

With a reproduction interval of only 4-5 days, if you wait for a test result before isolating contacts, you will do it too late. They will already have spread the infection.  

And many cases are asymptomatic, so you’ll miss them, anyway.

Testing is too unreliable. Too many false negatives, and too short a time from infection to infectiousness.

The only thing which works is keeping people apart so they can’t transmit it. In other words, physical separation measures proportionate to the risks in the local population – the only thing that has really worked in the UK appears to have been some form of ‘lockdown’.  

Writing this, on 1 December, I am acutely aware that we will be moving from a national lockdown to “tiered” restrictions – but case numbers are still terrifyingly high, and the R value far too close to one (albeit below one). If we relax restrictions, it seems near certain that R will again rise above 1; and with very high case numbers still, this will mean many more cases, serious complications (like long covid), and deaths. Such a shame when a vaccine appears to be around the corner.

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Opening schools and universities has a considerable effect, increasing transmission of the virus.

Children, schools, universities

It seems abundantly clear, now, that opening schools and universities has a considerable effect, increasing transmission of the virus.[3, 4]   It has been decided that we will have to live with this increase in transmission, because schools and universities are so important. I have some views on this.[5]

It has also become clearer that children are as likely to be infected as adults, and are probably as, or nearly as, infectious – despite earlier (rather wishful thinking, based on very little good quality evidence) claims to the contrary.🔷


References

  1. Cevik M, Tate M, Lloyd O, Maraolo AE, Schafers J, Ho A. SARS-CoV-2, SARS-CoV, and MERS-CoV viral load dynamics, duration of viral shedding, and infectiousness: a systematic review and meta-analysis. The Lancet Microbe, DOI: 10.1016/S2666-5247(20)30172-5.
  2. Raffle AE. Screening the healthy population for covid-19 is of unknown value, but is being introduced nationwide. thebmjopinion, 2020; Updated 09 Nov 2020; Accessed: 2020 (12 Nov).
  3. Brauner JM, Mindermann S, Sharma M, Johnston D, Salvatier J, Gavenčiak T, et al. The effectiveness of eight nonpharmaceutical interventions against COVID-19 in 41 countries. medRxiv 2020:2020.05.28.20116129, DOI: 10.1101/2020.05.28.20116129.
  4. Haug N, Geyrhofer L, Londei A, Dervic E, Desvars-Larrive A, Loreto V, et al. Ranking the effectiveness of worldwide COVID-19 government interventions. Nature Human Behaviour 2020, DOI: 10.1038/s41562-020-01009-0.
  5. English PMB. Should schools close to prevent Covid-19 transmission? Politics Means Politics Magazine, 2020; Updated 25 Nov 2020; Accessed: 2020 (25 Nov).


Dr Peter English, Public Health Doctor. Particular interests in vaccination and health intelligence.