July 9 covid-19 update

The story this week is once again that of two runaway epidemics. Three weeks ago I noted that South Africa was on track to surpass Italy's number of cases within 3 weeks. South Africa did surpass Italy today, both in terms of total confirmed cases and in cases per capita. (Recall that South Africa and Italy have very similar population sizes, and that these graphs are showing cases by week of the epidemic. Week 1 is the week at which the country passed 100 cases. Italy reached 238,159 in week 17 of its epidemic, and South Africa reached 238,339 cases today, which is week 17 of its epidemic.) Of course, these numbers tell us only about the number of confirmed cases of SARS-CoV-2, and not about actual number of infections. But what's important is not so much the number of cases (which we know is a small fraction of total infections), but the trajectory of the curve. South Africa's number of cases has been doubling every 2 weeks since week 2, and this trajectory shows no sign of slowing. This is most evident in the second graph in the left column (log scale). (If you're viewing on your phone and not seeing columns, it's the third graph.) Remember that exponential growth shows up as a straight line when plotted on a log scale - and look at how straight South Africa's line is in this graph, meaning there has been no slowing of the epidemic's exponential growth.

As we've discussed before, it's more important to pay attention to the shape of the epidemic curve, than the actual number, because even small numbers will rapidly become huge numbers under exponential growth. I'm reminded of the story of the grains of wheat (or rice) on a chessboard. If one starts with 1 grain on the first chess square, and doubles this to 2 grains on the second square, and doubles again to 4 grains on the third square, and so on, by the time one reaches the last (64th) square of the board, there are 18 quintillion grains of wheat, which Wikipedia tells me is 2000 times annual world production. Of course, a population would reach herd immunity long before an epidemic had doubled 63 times. The fact remains that South Africa's exponential growth (doubling every 2 weeks) will quickly catapult the number of cases and deaths to huge numbers, unless that growth can be slowed. At the current trajectories in the U.S. and South Africa, I predict that South Africa will have as many cases as the U.S. per capita within 3 or 4 weeks. The silver lining is that South Africa continues to see a much lower case fatality rate (CFR) than the U.S. or Italy, due to its younger population. Even so, unless transmission can be slowed, South Africa will reach the catastrophic death rates seen in Italy, perhaps in as little as 2 months.

The U.S. passed 3 million cases this week, driven by rapid transmission in a handful of states that were among the first to reopen. Here's a visualization from the New York Times. (As a reminder, the NYT has a treasure trove of detailed, constantly updated visualizations showing the epidemic in the U.S. and world.)

Hospitals are filling up, although we haven't yet seen a surge in deaths nationally (which are still hovering under 1000 a day). The Atlantic reports that Arizona, Florida, and Texas are already seeing a surge in deaths and predicts that we will see deaths climb further, but also points out some reasons why deaths may stay lower than the counts of around 2000 per day we saw in April. The average age of a person diagnosed with the virus is decreasing, more testing is discovering more relatively mild cases (although testing is still lagging behind the growth of the epidemic), and treatment protocols (and thus clinical outcomes) are improving over time. Summer weather may also be giving us something of a reprieve in the northern hemisphere, so go to the article if you want to read a longer explanation of that.

Last week I discussed the issue of kids returning to schools, and quoted extensively from economist Emily Oster. As it turned out, Dr. Oster was a guest on the July 2 edition of one of my favorite podcasts (Slate's Political Gabfest), and it's a segment well worth listening to (start listening at 27 minutes). She gives data on the harms she sees in keeping kids out of school, including long-term effects on their well-being. She also presents the idea of a "risk budget" and argues for spending that "budget" on kids returning to school, which is very similar to my discussion of risk "points" in my July 2 post.

On June 30, the American Academy of Pediatrics (AAP) released guidance calling for schools to resume in-person instruction as much as possible; apologies I didn't mention this last week. The New York Times carried a lengthy interview with the author of the guidance and you can link to the guidance through the article itself (or here). I found this paragraph in the NYT interview to be the most compelling:

• "Here in Colorado, I’ve been following our state health department website very closely. They update data every day and include the outbreaks in the state they are investigating. As you can imagine, there are lots and lots in long-term care facilities and skilled nursing homes, some in restaurants and grocery stores. There have been a total of four in child care centers, and we do have a lot of child care centers open. In almost every one of those cases, transmission was between two adults. The kids in the centers are not spreading Covid-19. I’m hearing the same thing from other states, as well." (Dr. Sean O'Leary, quoted in the New York Times)

In the report itself, I was interested to see attempts to make recommendations more realistic and to balance costs with benefits. For example, the AAP states that 3 feet [1 meter] in between desks is sufficient, with the rationale that insisting on 6 feet [2 meters] between desks may make it necessary to limit class sizes and keep children home, a net loss to children's health that will outweigh the gains of that extra distance. The AAP report recognizes that younger children (under 5) will likely not be able to maintain social distance or wear masks, so does not prioritize those measures for this age group. The report is also skeptical of temperature checks, noting that the costs (lost instructional time, possible clustering of kids) may outweigh the benefits, especially as many (maybe most) kids who get covid-19 will not get a fever.

Another hot topic I've been reading about this week: whether SARS-CoV-2 is being spread through microscopic droplets called aerosols (outside of healthcare procedures such as intubation which produce aerosols), or whether it is only spread through larger, heavier droplets which are exhaled and fall to the ground fairly rapidly. This is a critical question, as maintaining a 6-foot distance from other people and wearing a mask may not protect us from aerosols, which can travel further than 6 feet and pass through cloth masks. The New York Times summarizes the debate, with the World Health Organization (WHO) on one side (maintaining that SARS-CoV-2 is not being spread through aerosols outside of healthcare settings), and hundreds of scientists on the other side, arguing in an open letter to the WHO arguing that the virus is being spread through aerosols. It's alarming to read that aerosols can easily travel the length of a room, or that SARS-CoV-2 has been found to survive in aerosols for 16 hours in a lab setting. If you want to do a deep dive into the research, this article provides a really comprehensive look at what we know to date about droplets in various settings.

In my view the take-home message is that masks and maintaining a 6-foot distance may not be enough to eliminate risk, and that a key part of reducing risk is increasing ventilation as much as possible - through installing better ventilation systems with air filters (obviously not always feasible), being outside if at all possible (outside is always better than indoors), or opening windows (at the very least). Because risk of infection is related to the dose or amount of virus a person encounters, anything that will increase airflow and dilute the amount of virus in the air is helpful.

A final recommendation of something well worth reading: a story from the Washington Post about the spread of the virus around the world (with some great visualizations), which also contains some very human stories (with lots of pictures) of families who are struggling to cope with the pandemic in 6 countries.