Christmas II

Now that data has fully filled in for the weeks following Christmas, it confirms that the Christmas case bump was indeed temporary, and Wisconsin has returned to a gradual downslope of infections. I expect this trend to continue, although it is possible the new virus strain will arrive to interrupt it.

So this is Christmas (bump is over)

Daily cases by test or symptom date started increasing after Christmas, reached a peak about a week into January, and have been declining since.

As in previous posts, I am displaying the cases by test or symptom date, instead of reporting date, to avoid any effects from reporting delays. (For example, death reporting is now running way behind the actual date of death.)

To check whether this pattern may be due to changes in testing, rather than infections, we can again look to Milwaukee County, which publishes both cases and tests by test date. (The state publishes test numbers only by result and report date, not test date.)

Milwaukee shows a similar increase in cases after Christmas. As for testing, the holidays themselves have lower numbers but the other days around them are pretty consistent. So I’ll sum only the consistent Monday through Wednesday numbers and plot cases and positivity rate together.

Both measures increased after Christmas, and continued going up a bit in the week after New Year’s Day. After that, though, they resumed their decrease on about the same slope as before the holidays.

So this data shows that Christmas caused a modest but temporary bump in the number of infections, because (I believe) activity around the holidays was also only temporary.

The outlook for Wisconsin

I expect the gradual downward trend in infections and deaths to continue, possibly until we have mass vaccination and the pandemic is effectively over. Our current combination of partial population immunity, prevention measures, and now vaccination is strong enough beat the virus back. There are a few possibilities that could still interrupt this path, however.

The first possibility is that when colleges go back into session this week, it will cause a spike in cases similar to what we saw in the fall. As long as this spike is confined to college campuses, though, I don’t think it’s something to greatly worry about. I mean, Tommy Thompson and Becky Blank should worry about it, but based on the fall I think it’s unlikely to kick off a wider increase in spread.

The second, more dangerous possibility is the arrival of a more transmissible coronavirus strain to Wisconsin. One strain, B.1.1.7, has become widespread in the U.K., and scientists think that it is responsible for a fast rise in cases even in the face of strong restrictions on activity. This new strain has been detected in the United States, but is probably not yet widespread. If it were to get a foothold in Wisconsin, its higher transmissibility could return us to increasing infections.

If this were to happen, my guess is that we would see the effects in Milwaukee and Madison first, just as those areas saw the first major outbreaks of the original coronavirus. The new strain would have had to arrive here from somewhere, and that is more likely to happen in larger cities with more frequent travel out of state.

So far, however, I see no signs of an outbreak of the new strain here. So my hope is that more vaccinations, and spring, arrive before it does.