Hi Everyone,
Mixed messages today. NY continues to do great, but the rest of the US and NC are showing some possible danger signs.
US Cases
While the number of new cases continues to decline in NY, the number in the rest of the US continues to stay flat (Fig. 1). One piece of good news is that the number of tests per day keeps increasing, slightly in NY, and substantially in the rest of the US (Fig. 2). When new cases are corrected for number of tests, the number of new cases per test continues to decline in NY and the rest of the US (Fig. 3), but there are signs this decline may be slowing, or even plateauing, in the rest of the US. If so, this would suggest that the real number of new cases may also be plateauing, which wouldn’t be a good sign, and could reflect the beginning of an increase in cases associated with relaxing social-distancing measures. We’ll need to keep an eye on that.
A modified logistic growth curve still fits both the NY and rest of the US data quite well (Fig. 4). Projections from this fit indicate a leveling off of cumulative new cases per test around day 100. Specifically, for the rest of the US, on days 90, 116, and 149 (May 29, June 24, and July 27, respectively—these dates are about 3 days later than projected last time), 95%, 99%, and 99.9% of the total infections during the first wave of the virus will have occurred. On these dates, the minimum number of infections yet to come are 195,471, 53,609, and 9,799. On days 112 and 146, the expected minimum number of new cases will be 2,801 and 521.
Fig. 1.
Fig 2
Fig 3
Fig 4 Fig 5
US Deaths
New deaths per day in both NY and the rest of the US continue to decline (Fig. 6). For the rest of the US, this trend is significant (P= 0.0035 after day 45). At this point, the decline seems linear, and a linear projection suggests that new deaths per day will reach 0 around day 128 (6 July, about 1.5 months from now)—if the trend continues, of course. As I indicated last time, though, there is a lot of error associated with this estimate: it could be as late as day 245 (2 November). If it does continue, that would reflect essentially the end of the adverse effects of the first wave of infections.
Fig 6
NC Cases
You may have heard that the recorded number of cases yesterday and two days before that were the largest for NC since the beginning of the epidemic. This suggests the number of cases may actually be acceleration, which the 5-day moving average suggests (Fig. 7). Correcting number of cases for number of tests (Fig. 8), the number of new cases per test, which had been declining, is actually showing signs of beginning to increase again. This is especially evident in the 5-day moving averages. This would be a very bad sign, indicating that relaxing social distancing practices in NC may be leading to a new wave of infections. Admittedly, this trend is based on only the last three days of data, so we’ll have to wait and see if this trend continues. However, at the very least, it suggests that the decline in new cases per test (which I believe is proportional to the total number of recorded and unrecorded new cases) has plateaued, which is also not a good sign.
The fit of the data to a modified logistic growth curve is not very good (Fig. 9), probably because of the plateauing/increase in number of new cases per test. There are clear systematic deviations of the data from the fitted line. For this reason, at this time I am not using this fit to project cases into the future.
Fig. 7
Fig 8
Fig 9
Conclusions
Unlike last time, when the data gave me reason to be fairly optimistic, I am less sanguine with the new data. While NY is continuing to do really well, in terms of both number of new cases and new cases per test, we are seeing what appears to be a levelling off of the curves. This could reflect an increase in actual new cases per day, which could portend the beginning of a second wave of infections associated with “opening up”. We’ll need more data to see if this is a real trend, but we probably should know within a week or so.
In NC, things are even more gloomy, with the number of new cases per test looking like it may actually be increasing. This could also indicate a second wave, but again, we’ll know better in a week or so.
The main bright spot is that the number of new deaths in the US is declining. This is a real trend to root for.
Stay safe!