Did I just jinx the end of the flu season?

In my post 12 days ago, I made the "bold" claim that this year's flu season (which has been bad) had peaked, and was now declining based on data from the CDC and Google Flu Trends:

The good news is that both trackers indicate that the worst of the flu season may be over. It is too early to say for certain, but the number of cases or severity in both graphs appear to have peaked and is now declining. I will check both trackers next week to see if this downward trend continues.

This week I revisited both flu trackers. As a reminder, the CDC data are based on outpatient visits to hospitals because of flu symptoms, and the Google data rely on the number of flu-related Google Searches.

Figure 1. Flu tracker from the CDC based on outpatient hospital visits for flu symptoms (snapshot from 1/21/15). The 2014-2015 season (red line with triangles, see key) is compared to the past 4 seasons (from CDC).

According to the CDC graph (Figure 1), the flu outbreak this year (red line with triangles) has clearly peaked and is now undergoing a significant decline.

However if you look at the Google Flu tracker (Figure 2), there seems to be a small rebound in possible flu cases.

Figure 2. Google Flu Trends (1/21/15). This year (dark blue) compared to the past 6 years (link).

It appears as though after about a month of decline, flu intensity is increasing again. One question is why do the two flu trackers disagree (i.e. the CDC graph does not show the rebound)? It could be the the different data sources are giving rise to different estimates. Another possibility is that the Google tracker appears to be approximately one week ahead of the CDC, which makes sense because searches for flu can be tabulated in real time, whereas the CDC statistics need to be collected from various hospitals.

However closer examination of past flu seasons reveals that there are almost never two distinct peaks i.e. one peak followed by a significant decline and then a rebound to a new peak. Some years show more of a "shoulder" in which the decline might be interrupted by a transient increase before resuming the downward trend. My best guess is that this is the case for this year; there will be a modest uptick and then a continuation of the decline. I will check again next week.

Thus, it is likely that the worst is indeed over (and I did not jinx the flu season). Of course that does not mean your chance of getting flu this year is nonexistent; the probability is just getting lower. You should be as vigilant as ever. To avoid the flu, it is best to get your flu shot. In addition, wash your hands carefully and often with soap, avoid touching your eyes, nose, or mouth, and try to avoid close contact with sick people.

In summary, it is helpful that we can monitor the severity of each season's flu outbreak using these informative tools from the CDC and Google.