Second Covid-19 wave in California?

For the last few days, the newspapers have been full of reports of a “second wave” of Covid-19 cases in some states. California has been mentioned as one of those states. Using the California Department of Public Health’s numbers, I conclude that there is good news and bad news.

The good news is that, so far, there is no second wave in California.
The bad news is that the first wave isn’t anywhere near over.

Let’s look at some graphs.

What’s plotted above is daily confirmed Covid-19 deaths. The blue line is a 7-day moving average. A gradual decreasing trend is visible. Deaths are less likely to be missed than infections, but, especially early on, testing was in short supply so the confirmed deaths undercount the actual Covid-19 deaths. Deaths are also a lagging indicator of infections.

If we look at confirmed cases, we see a more-or-less linear rise since late March. If the first wave were receding, you’d expect to see the number of confirmed cases fall. Some have argued that the rise in cases is due to the rise in testing. We can get a small insight into that by looking at the number of positive tests divided by the total number of tests.

For the last two months, the positivity rate has been more or less constant. We don’t have enough information to interpret that precisely.

Another thing to look at is hospitalizations.

The CDPH’s terminology can use a little explication. Confirmed hospitalizations are those of patients who have tested positive. Suspected hospitalizations are those of patients who have not tested positive (probably because they have not been tested at all), but are suspected of having the disease. In the first month of the data, testing was extremely limited, resulting in a low number of confirmed hospitalizations.

In Monterey County, we have seen a recent increase in the number of cases: