October 11, 2021
Since my last letter to you on Thursday, ADPH has reported a total of 3,088 new cases over 4 days, down 38% from the 4,953 cases reported for the same 4 days last week. Alabama’s 7-day average is now 1,024 cases per day, a 36% decline from the prior week. Compared to 2 weeks ago, new reported cases have declined 60%. Incredibly, the pace of Alabama’s decline over the last weeks is the fastest in the nation.
Alabama’s hospitalization rate also has plummeted. We now have 839 confirmed Covid patients in 103 reporting hospitals, or 8.2 patients per hospital. That amounts to a 48% drop from the 15.7 patients per hospital 2 weeks ago. Meanwhile, Alabama is averaging 55 deaths per day, 52% below the rate of 116 deaths per day just two weeks ago.
What accounts for this steep decline, which is also exhibited in other parts of the Deep South? This pattern of rapid increase in cases, followed by an equally rapid decline, is similar to what was seen in India, the U.K. and the Netherlands. I have heard two theories to explain this phenomenon.
The first is the “herd immunity” theory - namely, that Alabama and the rest of the South suffered so many Delta cases in August & September that the variant ran out of available “wood to burn”. I’m skeptical of this theory. Approximately 250,000 confirmed cases were reported in Alabama during the last 90 days. Considering asymptomatic cases and moderately symptomatic cases, the CDC estimates that 1 of every 4.2 Covid cases is publicly reported. If true, that would mean Alabama has had as many as 1.05 million cases in the last 90 days. If you add that number to the State’s 2.15 million fully vaccinated individuals, then up to 3.2 million of the State’s 5 million residents arguably have developed Delta antibodies, leaving 1.8 million others (36% of the population) who have neither been vaccinated nor infected by the Delta variant. The number of people without antibodies may actually be higher since a fraction of vaccinated people got infected with the Delta virus.
But wait, you say, what about the infections that occurred before Delta appeared this summer? How much do those infections contribute to “herd immunity”? Probably not much. First of all, the Delta variant has adopted mutations which partially cloak it from the immune system’s antibodies. Although the mRNA vaccines have been engineered to counteract those mutations to some extent, the same cannot be said of natural immunities. Second, immune responses to Covid have been found to wane in the months following both vaccination or infection. While there are reams of data on the immune response to vaccines, experts disagree on how much protection a prior infection delivers. In fact, not everyone who gets infected will even have natural immunities. A recent CDC study of those with prior infection found that 36% did not form any antibodies against the virus (in contrast to the 100% immune response of non-immunocompromised people with at least one dose of an mRNA vaccine).
So, I’m not persuaded that Alabama is currently benefiting from “herd immunity”. I may be wrong, but I find the second theory more compelling - namely, that Alabama’s decline has been driven primarily by a change in human behavior. It is fairly clear that pandemic fatigue - i.e. people letting their guards down when cases were low - played a role in Delta’s rise, which coincided with the return to school. Initially, many school districts were caught by surprise and resisted masks, leaving the highly contagious Delta variant to take advantage of this lapse. Also important: hot and wet summer weather kept people indoors, where the Delta variant could spread more easily. As the weather has moderated and outdoor activity increased, the contagion naturally diminished.
This “human behavior” theory is supported by an examination of the states where Delta has migrated. Seven of the 8 states with the highest per capita infection rate in the country over the last 14 days are cold weather states - (in order) Alaska, Montana, North Dakota, Wyoming, West Virginia, Idaho, Minnesota & Wisconsin. Meanwhile, Hawaii, California, Florida & Louisiana - all warm weather states - are 4 of the 5 states with the lowest per capita infection rates in the same period. Alabama has the 10th lowest rate of infection over that 14-day period.
If, as I believe, altered human behavior is the primary cause of Alabama’s recent improvements, not achievement of herd immunity, then it shows we have a measure of control over what happens next. As the weather gets colder and we go back indoors, we will face greater risk that Delta or some other variant will return. Yet, if we are willing to take adequate precautions this winter, like mask-wearing and other common sense measures, then we can be the masters of our own destiny. The totals:
9/28 - 1,984
9/29 - 2,141
9/30 - 1,702
10/1 - 1,845
10/2 - 1,480
10/3 - 892
10/4 - 736
10/5 - 1,549
10/6 - 1,272
10/7 - 1,262
10/8 - 1,049
10/9 - 919
10/10 - 653
10/11 - 467