Risk of SARS-CoV-2 transmission from asymptomatic people in different settings

[bennevisplace]

The diagram above is from a review paper, published yesterday in the British Medical Journal bmj.com/content/370/bmj.m3223

The diagram brings together several variables which, according to the paper's authors, contribute to the relative risk of catching Covid in different social situations where in principle anyone nearby could infect you.

THIS REVIEW'S KEY MESSAGES:

- Current rules on safe physical distancing are based on outdated science

- Distribution of viral particles is affected by numerous factors, including air flow

- Evidence suggests SARS-CoV-2 may travel more than 2 m through activities such as coughing and shouting

- Rules on distancing should reflect the multiple factors that affect risk, including ventilation, occupancy, and exposure time

While you can use this info to moderate your own behaviour, DON'T expect the key messages to be incorporated into official control measures any time soon.

[LeoPa]

As per my humble opinion this is an academic debate needlessly complicating the subject. I can't imagine people running around with a risk assessment sheet and measuring distances between each other as per the given specific conditions. The 6 feet from each other guideline is good enough as long as everybody wears a reasonable quality face covering while not sneezing and coughing. If someone does, just run 🏃‍♀️. My Bro spent a minute sitting on a couch at abt 2 feet talking to someone who later proved to be positive and he did not contract it. A certain viral load is needed for infection, just a virus or two won't do it. It's not as contagious as the regular flu.

[bennevisplace in reply to LeoPa]

Hi LeoPa.

I think there is more to this than an academic exercise. The BMJ is primarily for medics, and surely the authors' target audience is those in authority, via their learned advisers ("We are always guided by the science"). The authors want to persuade decision makers to consider control measures in addition to 2 m/ 6 ft and more recently face coverings, at a time when people have begun to mingle in enclosed spaces again.

Every national government is desperate to re-boot the economy. Fine, but perhaps they should pay more attention to safety in re-occupied buildings, if they want to head off a resurgence in Covid cases that could put us back to pandemic-economic square one.

In the UK the government's health and safety regulator HSE has issued Covid guidance for the workplace. It covers social distancing, PPE, hygiene, risk assessment, protecting the most vulnerable, etc. Do they cover the risk of airborne transmission, the need for work areas to be well ventilated, avoid recycling of air, sterilise air-conditioning systems etc? No they do not. In the UK it is employers, not government, who are legally liable for safety in the workplace, and employers should be getting proper advice.

If the authorities ignore the key messages of this review paper and other scientific studies, that is just asking for a second wave. Most people will come out of this without catching the virus, and most of those who do catch it will suffer no long term damage. That leaves casualties in the many hundreds of thousands, and millions of clinically vulnerable people in a state of permanent trepidation. That's why I thought this paper is relevant to the CLL forum.

[LeoPa in reply to bennevisplace]

Hi bennevisplace, yes it is relevant. The problem is laypeople don't follow the simple rules either. Protests in Germany against the rules? Conspiracy theorists popping up in my place who don't believe the virus is real because nobody knows an infected person personally? Ridiculous as they are these are real people behaving like that. Governments are not likely to adapt these recommendations because they would take a very long time to implement and everyone expects a vaccine to be available soon. That's what I meant by academic debate. I might be wrong but I expect nothing to come out of it. Trepidation will be our daily bread till a vaccine is available.

[bennevisplace in reply to LeoPa]

Yes, I agree that laypeople don't necessarily follow the rules. Perhaps they would do better if government policy was proactive and consistent, messaging loud and clear, and people could actually see rule-breakers sanctioned? Compared with smokers, superspreaders can take far more liberties and get away with it!

I think this paper is timely because at this point we have learned a lot about Covid and we have one chance, as the economy reawakens, to use our knowledge to make workplaces, shops, hospitality and entertainment venues, transport systems etc as safe as they can be. I can't agree with you that this would take a long time, though certainly precious time has been lost.

If official control measures remain behind the curve, we CEVs must do what we can to protect ourselves. A vaccine for Christmas? One can wish.

[AnneHill in reply to bennevisplace]

This shows that we all have to take responsibility for ourselves. We can wear a mask in public, wash hands, use hand gel and wipes and social distance. Be careful not to touch our faces with unwashed hands.

What we cant control is the air we breath and recirculated air conditioning.

We have booked a hotel by the sea for a few days. Will come back early if need be. We have found coffee shops to be strict with spacing and cleaning and I am really hoping this hotel is the same.

Ventilation is really important and I open windows and doors at home. That is the one thing I will worry about when using the dining room. I am expecting the tables to be socially distanced and will only take my mask off to eat.

We are taking a risk I know. Anne uk

[bennevisplace in reply to AnneHill]

Anne, good that you're giving thought to all this in advance. So when the time comes you can relax and enjoy your break. It's important to get away from time to time. Have fun.

[AnneHill in reply to bennevisplace]

Thankyou, Anne uk