Thread by @jburnmurdoch

2) Proximity of encounter matters, but it’s tangled up with duration, repetition & ventilation.

People worry about a runner passing them too close, but half a second of 1m contact outdoors is less risky than several minutes of 2m contact, especially with poor ventilation.

3) Plenty of studies showing masks reduce risk.

A Lancet meta-analysis found masks reduce infection by 80% (similar to effects of 1m or more of distancing) but NB this was based on surgical grade masks

With homemade or basic cotton masks, effect will be smaller, but still helps

4) Evidence also points to raised voices, singing etc as being a risk factor, as these increase the likelihood of spreading more droplets and spreading them further.

A study found one infected person infected 52 others at choir practice.

Think of all these as tools you can use to minimise risk to you & others

Have to use a poorly ventilated bus/train for 20 mins? OK that’s indoor, duration & ventilation out of your control, but you can combat those risk factors by wearing a mask, trying to distance & not talking

...or get off the train/bus a stop earlier to minimise duration in that higher-risk environment.

Meeting your bubble for a picnic? Meet outside, distance, masks when not eating.

Going shopping? Make sure it’s well ventilated, mask up and don’t spend longer inside than necessary

Essentially, think about which of these elements — proximity of contact, duration/repetition of contact, ventilation, outdoor vs indoor, face covering, talking — are in your control in any given situation, and which aren’t, and pull the levers available to you to reduce risk.

This should also help to explain why certain parts of life will return to normal faster than others.

Pubs and cafés can open beer-gardens and outdoor seating before indoor service resumes, as it’s easier to distance outdoors and lots of good air circulation.

Tennis and running have been allowed in the UK for weeks, but gyms remain closed.

The former are naturally distanced and outdoors, the latter are multi-person environments with lots of heavy breathing indoors.

We also know the overwhelming majority of Covid-19 infections come from a few super-spreading events (~80% of new infections from ~20% of index cases).

If you consider overall risk as risk of infection x number of possible infectees, this makes mass events especially risky.

Transmission risk is high in households, but at worst you infect a handful of easily-traceable others.

An infectious person at a sports match, theatre, nightclub could spread the virus to dozens in one go, and tracing would be harder.

Here ends the thread, I think.

Remember your toolkit:
• Outdoor vs indoor
• Distance
• Duration
• Ventilation
• Masks
• Talking/shouting
• Avoid mass events

In any given situation some of these may be out of your control, but control what you can.

fixing typo from tweet 1):

Transmission is much more likely indoors than outdoors, and super-spreading risk higher indoors

Study traced contacts of 110 infected people and found indoor contacts 19x more likely than outdoor to spread virus

If you can do an activity outdoors, do

Sources:
• Indoor vs outdoor medrxiv.org/content/10.110…
• Duration/ventilation researchgate.net/publication/34…
• Proximity, masks (and check the studies used in the meta-analysis) thelancet.com/journals/lance…
• Singing cdc.gov/mmwr/volumes/6…
• Super-spreading researchsquare.com/article/rs-295…

And some thanks:

First of all to @mugecevik who first collated and shared all of these papers [

https://twitter.com/mugecevik/status/1257392347010215947

], and second to m’colleague @Mikepeeljourno who led the stories at top of thread

And here we have that covid transmission toolkit being ignored as comprehensively as possible:
• Indoor
• Close contact
• Extended time
• No masks
• Lots of loud talking
• Large number of people

Result: 16 new infections in one go news4jax.com/news/local/202…