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Lessons from the CDC: How to Make Judgements Without a Denominator



So, the month of July in Cape Cod, MA has really screwed everything up. If you haven’t been paying attention to the mainstream media over the past few weeks you would be unaware that a very large group of vacationers descended upon the shores of Cape Cod Massachusetts, as they’ve done for generations, to enjoy the sun, beaches, and other scenery this month.


You may have also been unaware that demand for leisure travel has never been higher. Americans spent almost all of 2020 in and around their homes. They had money deposited into their bank accounts. They refinanced existing mortgages to lower monthly payments and most took equity out of their homes. They were given forgiveness on those payments for a while, as well as some payments on student loans. The middle and upper class have been sitting on a lot of cash and Americans love to spend money.


With 50% of American adults vaccinated and COVID cases, hospitalizations, and deaths plummeting the time for hibernating was over.


Barnstable County has reported a COVID outbreak that occurred during the month of July. Between July-14-28, 468 Covid cases were identified for a daily average of about 33.


· Of these 468 cases, 74% were vaccinated.

· There were 4 hospitalizations.

· There were no deaths.


The CDC also did this funny thing where they measured viral loads in the vaccinated individuals that became infected. They discovered the viral loads were the same in infected vaccinated individuals as unvaccinated. This was a “pivotal discovery.”


· This scared the crap out of everyone.

· It has now become the most common anti-vax defense I’ve heard for the past week.

· “the war has changed”

· It’s completely irrelevant.


This prompted the CDC to revert to many of the physical barriers that were in place prior to the vaccine. They are now recommending individuals that have been vaccinated wear masks in areas of high transmission. Our K-12 children, who were likely going to be spared masks this schoolyear, now must wear them again. Masks are mandated in healthcare facilities, so no reprieve for my staff or myself anytime soon. And I’m wearing one in the grocery store again.


I’ve heard all kinds of commentary about this outbreak. The evidence has been described as “strong”, “convincing”, “substantial”, etc…But what questions do these numbers actually answer?

Not many.


These numbers say that even if you’ve been vaccinated there is still a chance you can transmit the virus.


· We already knew this. The vaccine is not 100% effective, but it is close.


They also say, if you’ve become infected with the virus it replicates many times over.


· We already knew this.


There isn’t much else you can answer with this data.


The CDC admits they do not know how many people have visited Cape Cod this July. The CDC also admits they do not know how many of these visitors are vaccinated. They estimated around 70% (true number is likely 50-55%). They do not know how many people were infected beyond these 468 cases as well.


The CDC’s response to this outbreak is a head-scratcher.


Maybe I have too much faith in the vaccine. Maybe I’ve become naïve. I’ve always expected little insurgencies from COVID, but they would be quickly squashed by natural immunity and the vaccinated.


The biggest issue with this “data” is there is no denominator. The modern-day human uses statistics and mathematics to help us understand risk. We use percentages and fractions every day to help us explain the world around us. I’m sure you are familiar with them. The percent chance of rain today, percent chance of making that 3-pointer, percent chance of plummeting to your death while sky diving. We use these all the time.


They consist of a numerator, and a denominator. The numerator represents the number of events. The denominator represents the number of tries. The CDC has the numerator, but no denominator.


We can venture a guess as to how many people visited Cape Cod during the month of July. In 2020, Cape Cod had 776,924 visitors. That’s 2020! Hello, COVID lockdown. In 2015, 900,628 visited the area. It was estimated that 1.4 million people were expected to descend upon the Cape Cod area in 2021.


I’ll be generous and use an average of those 3 numbers. That’s 1.025 million visitors this year. I’m going to cut this number in ½ because only ½ the month is accounted for.


Percentage of infected (468 x 0.74)/ number at risk. 346/512,934 = 0.067%


The vaccine performed magnificently!


This is likely at a vaccination rate below 70%.


There are a few limitations to this line of thinking. First, it is an estimate of the number of visitors. Also, these numbers are for Barnstable County, not specifically Provincetown. Second, I do not know if all the visitors spent time indoors in a poorly ventilator structure. What I do know is that many of the bars and restaurants are stereotypical small town restaurants and bars. Not exactly Walmart. Third, asymptomatic individuals probably did not seek out a test. So, the numerator could be a little higher.


Even with these limitations, the vaccine performance is very impressive. The vaccinated risked very little by cramming themselves onto a small strip of land and mixing it up with a bunch of unvaccinated strangers.


Next, the viral load issue. If you become infected with a virus, it will replicate billions of times. If you’re infected, your defense system was faulty. Either you were unfortunate and did not get an appropriate response to the vaccine, or your neutralizing antibodies have worn off. You are in the window period in which your immune system is manufacturing them again. Viral loads are only helpful during treatment of chronic viruses like HIV and Hepatitis C. We use them to understand if our treatment is effective, not to establish if you are infected.


There is no reason to suspect that a virus that successfully infiltrates a host would replicate any slower simply because the host had a vaccine in the past. Either you have neutralizing antibodies present or you don’t. Until the memory B cells start manufacturing antibodies again the virus will replicate the same way it always does. I’m not sure why this is a “pivotal discovery.”


The CDC director was clear in her messaging “the war has changed.” And they changed their position based on this “pivotal discovery.”


It is this author’s opinion that this was not based on any pivotal discovery or great data. This is information that was already known, and this pivot sure kicked up a whole lotta dust. This was a judgement call. Which is fine. The CDC is full of infectious disease doctor’s and epidemiologists. They are notoriously paranoid about infectious diseases. And they should be. But stop calling stuff like this “pivotal data,” or “science.” They are looking at patterns and making judgement calls. The same way your local weatherman does.


Whether its intentional or not, these judgement calls continue to undermine the effectiveness of vaccines and frustrate many Americans. I’m not concerned if one of my patient’s gets a cold from COVID. I’m worried if they have a chance of getting seriously ill or die from it. Which the vaccine has proven repeatedly that it stops these events at an incredibly high rate.


News media outlets and the CDC continue to drive a narrative that these vaccines are something less than what they are. They are incredibly effective and safe. Over the past week COVID “breakthrough” infections are highlighted every night on cable news. At the end of each story there’s this little disclaimer “breakthrough infections remain extremely rare.” Why do we spend so much time talking about them? The story is really simple. Unvaccinated hospitalizations outnumber breakthrough hospitalizations by about 1000:1. That’s the graphic. That’s the headline. In the vaccinated, cases are rare, hospitalizations rarer, and deaths are exceedingly rare. That’s the narrative.


The war has not changed. If you’re a vaccine hold out, you’re a target for COVID, and it can wreck your world. If you’re vaccinated, or recovered from infection, you’ve already won. The odds are heavily in your favor. Covid has virtually no shot against your immune system. That doesn’t mean you can’t still get infected if you’ve been vaccinated. But it does mean that your immune system is ready to strike at a moment’s notice and win the war.

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