On Valentine’s day I remarked about the impressive drop in COVID-19 infections observed since late December. The media has picked this up and suggested many reasons behind this fall in infections. Many don’t make much sense, especially citing a change in seasonality of infections since winter “seasonal” increases in respiratory virus infections are usually not resolved by January or February. And as I now look at the foot of snow and seven-degree temperature outside my window in Ann Arbor, winter is not over yet!
The most interesting question, however, is whether we are now seeing some effect from the vaccines. The Israelis saw an effect from their vaccination campaign within six weeks, but they immunized more people in a shorter time. Like Israel, the U.S. is immunizing only with highly effective synthetic-mRNA vaccines from Pfizer-BioNTech and Moderna (Israel used only Pfizer), which also may accelerate the impact. Regardless, since both countries also focused on the most vulnerable populations and these vaccines are so effective at preventing clinical infection, it is not surprising that hospitalization and deaths could be rapidly reduced in the US.
In contrast, reducing overall infections with the vaccine requires reducing not just clinical infections but also asymptomatic infections and preventing transmission of infection by immunized people. While there have been suggestions of this happens with vaccination from the clinical trials, and most physicians feel it does occur, the data is not conclusive. In fact, the drop in infections we are now observing may be the best indication that vaccination and prior infection are truly preventing transmission of infection.
I have previously suggested infections would start dropping when a significant proportion of individuals is immune to the virus, much less than the numbers suggested for “herd immunity.” Is that what is happening now?
The CDC is indicating that about 25 percent of adults have COVID-19 antibodies from an infection. That is a significant percentage of the population, and it is likely much higher in areas where infections have been raging. We also have 10 percent of adults who have received vaccine shots since December. That means we have a third of the population protected from infection at this point!
If Dr. Fauci is correct, we will add about 10 million immunized adults every week. That means in only 8 weeks over half of American adults will have some kind of protection to COVID-19! That will be mid-April! I think that at that point we should see a more significant drop in infections from induced immunity.
How about variants? Clearly AstraZeneca’s vaccine is less efficacious against the variants, but Pfizer’s and Moderna’s appear more effective. So as long as the U.S. focuses on the RNA vaccines for the most at-risk individuals, variants should be controlled in the near term. Even in England, which is using AstraZeneca’s vaccine, infections with the UK variant (which is now 96% of all COVID-19 cases) have markedly dropped. That may be related to the Pfizer and Moderna use.
So, the pandemic isn’t over, don’t toss your mask, but we may finally have turned the corner.