Since September, NYC COVID-19 infection rates have been mostly increasing. This has lead to a spike in news articles, such as New York City sees 'very worrisome' spike in coronavirus infection rate. How worrisome is it, really? Let's look at the data.
Here's the 7-day rolling average of the number of cases per day since the drop off of the first wave in June:
In the beginning of June, we see the tail end of the drop off in the number of cases per day of the first wave. This in the impact of the mitigating measures taken at that time, such as the lock-down, social distancing and the use of masks. This left us with about 325 cases per day. There was a small increase in the number of cases per day in mid-July, peaking around 375, after which the number of cases per day dropped down to under 250.
Starting in September, we see a rise in the number of cases per day. It has steadily increased, peaking at 550 cases per day on October 5th. Subsequently, it dropped down to 450 cases per day and started rising again, hitting 550 cases per day a second time on October 29th. Given that this last peak was less than a week ago, we can expect it to rise higher as additional reports for that date arrive (for issues with delayed data, see Covid-19 NYC Stats - Not What They Seem).
People are calling this rise since September a "worrisome second wave", as exemplified in the article cited above. But, to put this rise in perspective, we need to compare the data leading up to the latest peak to the data leading up to the first peak.
Here's the 7-day rolling average number of new cases per day leading up to the new peak:
As you can see, for the recent peak, it's taken about 4 weeks to double. We were at 250 cases per day at the beginning of September and didn't hit 550 cases per day until the end of the first week of October.
Compare this to the beginning of the pandemic. On March 10th, there were almost no cases per day. Over the course of one week, the number of cases per day jumped up to 1,000. Two days later we were experiencing 2,000 cases per day. Three days later we hit 3,000 cases per day, and 5 days later were seeing 4,000 cases/day. The peak was over 5,000 cases per day.
So, compared to the first wave, the recent peak is more of a ripple than a wave. The rise through September is probably due to the school openings and easing of general restrictions. Similarly, it would not be surprising if the rise at the end of October is from people preparing for and celebrating Halloween. If this is the case, we should see the counts subsequently dropping in November and rising again around Thanksgiving.
While we still have to be careful, it should not be unexpected that between school openings, restaurant openings and holidays, we'd see some additional growth. But it looks like the social distancing measures are continuing to do their work in keeping the number of cases per day reasonably low. In general, we should expect the number of cases per day to rise somewhat and then stabilize at new levels as social distancing measures are eased. And we should expect that rates will rise as we approach commonly celebrated holidays and subsequently fall off.
Should we call this rise a second wave that needs additional mitigating steps? It looks to me like the recent rise of infections per day in NYC is to be expected, and is a ripple, not a wave. The only big second wave we're seeing in NYC is in the media's portrayal of the ripple.
