Into the second wave
Author: Alex Weinreb
We are experiencing a massive increase in new coronavirus infections. After falling steadily from early April to the middle of May, the number of new infections has been climbing steadily upwards. The three-day average has exceeded 1,200 for the last six days, and is now more than double the highest point in April. There is increasing talk of a second lockdown.
This increase in new cases is not the result of increased testing. We know this because even though there has been a significant rise in testing (green lines below), with the three-day average exceeding 20,000 per day since July 1, there has also been a steady increase in the percentage of people who test positive (blue lines). That percentage is continuing to rise. It is fast approaching the highest levels seen in late March, though the number tested in that period never exceeded 7,000.
The cumulative effect of all these new cases is best seen by looking at trends in the number of active cases: new cases per day minus recoveries per day. At the peak of the first wave, there were around 9,000 active cases in Israel. We sped past that old record on July 2, and are now at around 22,300, with no sign of a slowdown. The number of active cases is climbing by more than 1,000 per day.
For planning purposes, one of the crucial questions we need to ask is: How much higher will this line climb before it flattens out and begins to fall?
Over the last week, the rate of increase in active cases has been in the 6-9% range (3-day average). That’s roughly equivalent to the rate of increase Israel experienced in late March and early April. If we assume that the trajectory of the current wave will follow the first, we can get a sense of how high this number of active cases will climb by applying the rates of growth observed during that first wave to the numbers of infected in the current wave. We can see the results of such an exercise in the graph below, under two scenarios.
Scenario 1 applies the series of daily growth rates seen in the March 28-April 28 period to the current number of active cases, allowing us to project the number of active cases to August 14. Under this scenario, Israel’s caseload will peak at around 66,000 active cases in early August. That’s about three times as many cases as we have today, and more than seven times the peak in April.
Scenario 2 replicates these estimates, but using daily growth rates ranging from April 3-May 3, a little later in the first wave. In this more optimistic scenario, we should start to see flattening of the active infection curve in the next few days. But even if that’s the case, Israel’s active cases will still peak at around 38,000 on July 28, more than four times as high as the maximum point of the first wave, before beginning a slow descent.
Unfortunately, we expect actual trends over the next few weeks to come closer to Scenario 1 than Scenario 2. There are two main reasons. First, the faster reductions in infection rates built into Scenario 2 were associated with complete closures enacted more than two weeks earlier (in the 3rd week of March). Even if we were to enact and enforce equivalent closures tomorrow, it would take some time to see effects on infection rates. Second, Covid-19 is mutating quite rapidly. An increasingly dominant strain of the virus globally—though it’s unknown to us whether this is the case in Israel—is more infectious than the original (Korber et al. 2020), which implies higher transmission rates given the same raft of protective measures. In a subsequent post, we’ll discuss whether this can confer some advantage. But in the short term at least, higher infection rates will clearly lead to more active cases.
Of course, each of these scenarios, as mentioned above, is based on the idea the current second wave will follow the first in terms of shape. That is not necessarily the case. Both the absence of closures and changes in likelihood of transmission at the biological level mean that active infections may climb well beyond the 66,000 outlined in Scenario 1. If that is the case, we’re all in for a much longer and more painful ride. . . Unless there’s a vaccine, which is the topic of one of the next blogs.
A final note to keep in mind. This upsurge in active cases does not translate into increased demands on ICU beds, medical staff, medical supplies, mortality or longer-term morbidity, on a one-to-one basis. The specific impacts depend, crucially, on who is infected, in particular on their age and other health characteristics. So far we’ve been relatively lucky. In a continuation of trends from Israel’s first wave, the new infections are much more concentrated among the young, especially people in their 20s. In fact, only 6% of the 3,200 new infections reported by the Ministry of Health on July 14 and 15 were aged 65 or older. Still, that in itself is almost 200 people. Likewise, 6% of 66,000 infections—where we could feasibly be in a few weeks—is roughly 4,000 people. If we have that number of elders among the infected, it will place an immensely heavy burden on the medical system.Back To Blog