Early on in the pandemic, social distancing measures were introduced, with various distances. The UK went for 2 m, the USA for 1.8 m (6 feet), Hong Kong 1 m, etc. None of these were based on much evidence, but we now know a lot more. COVID-19 is an airborne disease. Although more data is badly needed, it seems likely that somewhere between most, and almost all, infections are caused by breathing in virus, that an infected person breathed out seconds or minutes earlier. The virus is carried by tiny droplets suspended in the air. And most transmission is indoors.
Over the summer I am continuing to play around with my new toy: a CO2 meter. This measures the carbon dioxide aka CO2 in the air. A plot of the CO2 concentration over one complete day (Thursday 11th August 2022) is shown above. This is in my bedroom. The units are ppm = parts per million, so 400 ppm means that out of every million molecules in the air, 400 are CO2.
It looks likely that most, or perhaps almost all, COVID-19 transmission is directly airborne. An infected person breathes out the virus in tiny aerosol droplets, which someone else later breaths in. But people also worry about becoming infected from touching surfaces contaminated with virus. This has led to work looking at how long virus can survive on surfaces.
We are currently being a bit distracted from the latest wave of COVID-19 infections, by the latest new disease to hit the headlines: monkeypox. A bit grim but that is where we are. The two infectious diseases are very different. The number of cases of monkeypox is tiny, in comparison with COVID-19, and many of the cases are found in men who have sex with men.
I have been reading both students’ final-year-project reports and a report commissioned by the NHS. I don’t know whether to be happy or sad that some of our students can write better reports than an august panel that includes a number of members of Royal Colleges. On the one hand it is great to see our students doing so well, but on the other hand at any one time the NHS is treating millions of patients, and you would hope that infection control in NHS hospitals would have rather more competent oversight.
The British Medical Association (BMA) – the body that represents medical doctors – is producing reports on the COVID-19 pandemic, in consultation with their members. The first report is How well protected was the medical profession from COVID-19?. Summary here. As you would expect, it makes pretty grim reading and repeats the (well founded, I think) criticisms of the UK government’s response, such as inadequate PPE.
Teaching is now almost finished for this academic year. On Friday I had my last meeting with one of my project students. It was nice, he has learnt a lot and we said we’d next meeting at graduation in July. So I have a bit more time, and a new toy: a CO2 meter*. This measures the carbon dioxide aka CO2 in the air. The concentration of CO2 in the Earth’s atmosphere is about 400 ppm** – where ppm = parts per million. Out of every million molecules in the atmosphere, 400 are CO2. There is some evidence – although I am not sure it is very strong – that at CO2 levels above 1000 ppm your brain functions a little less well. In any event, CO2 levels allow you to estimate how well ventilated a room is.
Quantifying the absolute value of the risk of catching COVID-19 is very hard, not least as it seems likely that some infected people may be breathing out a million times more virus, than others. But estimating changes in risk is a bit easier, eg a reduction in risk due to ventilating a room. If we make some assumptions (see below), we can estimate the reduction in exposure to the virus, due to ventilation turning over the air in a room. This is plotted above. The y-axis is the factor by which exposure is reduced, i.e., two means that the exposure is halved, and so on. The x-axis is the number of times an hour ventilation replaces the air in a room. So two means the air in a room is replaced by fresh air twice an hour. The solid orange line uses (a fit to) data of Oswin and workers on the how long SARS-CoV-2 survives in the air. The prediction is that turning the air over three times an hour approximately halves the exposure to virus.
Above is a plot of the concentration of carbon dioxide (C02) in a bedroom in which one person is getting about 6.5 to 7 hours of sleep. Plot is as a function of time from when they go to bed to when they get out of bed, and is from a 2013 paper by Batog and Badura. The units are parts per million (ppm). For context, the atmospheric CO2 concentration is about 400 ppm, i.e., in the Earth’s atmosphere (i.e., outside our homes) out of every 1 million molecules, 400 are carbon dioxide*. In our homes and offices, the CO2 concentration is higher because we are all breathing out CO2. We breathe in oxygen (O2), use it to burn our food for energy, then breathe out the CO2 this produces. As far as I know, there are basically no set limits on CO2 concentrations but guidance for workplaces, schools, etc is typically that it should be no more than a 1000 ppm. As you can see, this concentration is exceeded for most of the night.
A year ago I wrote – with some surprise – of the UK government’s decision to downgrade the classification of COVID-19, so that it was no longer considered a “High Consequence Infectious Disease” (HCID). This was done right at the beginning of the pandemic in the UK, spring 2020. Very early on, COVID-19 was classified in this most-dangerous HCID category, but it was then downgraded. But I don’t think I was surprised enough.