Yesterday right after I posted, Mark Rasmussen sent me an article that ran in Science Magazine, one of the 2 most highly regarded science journals in the world. It’s a news article, not a peer-reviewed journal article, but it attempts to pull together information from different sources, and I think clarifies the picture regarding SARS-2 viral spread. The take-away message of the article is that while the R0 appears to be between 2.5 and 3 (more on that later), it’s not true that the average individual will pass the virus on to 2 or 3 others. Rather, most infected people don’t pass the virus on to anyone at all, rather a few infected people are “super-spreaders”, infecting a large number of people at once. There are many documented cases of super-spreading, from choir practices, funerals, concerts, fitness classes, and meat packing plants. The commonality appears to be indoor locations with lots of people in a small space, with some of them shouting or singing. While the risk in outdoor venues isn’t zero, indoor venues account for 19 times the number of super-spreading events, according to a Japanese study.
According to the article, SARS-2 has a tendency to cluster in this way more than other respiratory diseases such as the flu or colds. This may be partially because of the “viral load” effect mentioned in the Erin Bromage article I posted on May 12th. In that article, it appears that the initial number of viruses an individual is exposed to partially determined if they will be infected, and how sick they will get. This also explains why so many medical workers in Italy got very sick or died in the early stages of the pandemic. Many medical procedures such as intubation create a bloom of floating virus from a sick patient, exposing unprotected workers to high viral loads.
The science article suggests that while the virus is still dangerous and outdoor venues are not completely without risk, it may be appropriate to relax restrictions on some outdoor activities. So here’s my informed but not expert advice on how to adapt to life with COVID:
- Staying at home all the time may no longer be the best approach, although it was probably very helpful in the early stages of the pandemic. Going outside to get some fresh air and exercise is probably a good thing, although still not without risk.
- When doing outdoor activities, it’s probably OK to not wear a mask, but maintain at least 6-10 ft from others you don’t live with. Locations with a gentle breeze will help move virus away from you!
- At work or shopping, wear a mask when around others to reduce the viral load that you are wafting into air should you be infected without your knowledge. Any reduction in viral load will help.
- If you suspect you may have been exposed, contact your physician and see if you can get a test.
- If you have a yard, invite a few friends over for lunch or dinner at a safe distance. Since Summer is starting, an evening outdoor dinner will be a welcome break from the isolation. You may want to have your guests bring their own food and utensils. Don’t invite a large number of friends, and sorry to say, don’t invite those friends who can’t resist hugging everyone! Young children may require supervision to be safe.
- Now that restaurants are open in California, I would personally only be comfortable with outdoor seating at the moment. If you’re comfortable, visit your favorite local restaurants to give them some business, sit outside, and leave your server a big tip if you’re able!
- I am a church goer, and I want to see my peeps again, but singing in a congregation is still a high-risk activity. Churches will need to be creative to open up again safely. Consider lower density services without singing, and/or hold services outdoors.
Regarding the R0 value for SARS-2. I saw a CDC website last week that gave the R0 value as 2.5. After 10 minutes of looking, I couldn’t find this site again. The Sanche paper I’ve referenced before (High Contagiousness and Rapid Spread of Severe Acute Respiratory Syndrome Coronavirus 2, EID, July 2020), published in the official CDC journal, Emerging Infectious Disease, gave the R0 as 5.7. So the CDC itself seems confused about what the R0 number is. My guess is, it’s somewhere between 2.5 and 5.7. That was a joke. Obviously, this range is far too large to be useful, and 2.5 and 5.7 are very different as applied to an R0 number. 2.5 is a very infectious disease, 5.7 is a super-infectious disease.
I’ve mentioned this before, but I want to remind everyone. Herd immunity is only a goal when a vaccine is available. Seeking herd immunity when there is no vaccine is not a good idea, because it will put large numbers of people at risk. Additionally, I am generally very pro-vaccine, but because of the risks of side-effects with this particular virus, a vaccine may not be available for several years. We will need to adapt to this reality. My hope is that we will start seeing daily cases come down this Summer.
Don’t fear, but be smart,