The estimable John Hinderaker calls attention to an ominous looking chart. It shows the results of Covid-19 tests at Walgreen’s pharmacies. As he notes, “Walgreen’s must run an enormous number of covid tests, nationwide. So their data should be a pretty good sample.”
Your immediate reaction is probably like his: “There are several possible explanations here. The obvious one is that vaccination makes you more likely to catch covid.” But, on further reflection, that isn’t quite so obvious. For that explanation to be correct, Covid, or the vaccines against it, would have to be far different from all other infectious diseases or vaccines. Medical science isn’t infallible, but it has progressed somewhat beyond leeches and the four humours, so we ought to give the data more thought before adopting a theory that assumes medical ignorance. The superficial analysis doesn’t take into account two key points.
First, the results shown on the chart are for last week, over two years after Covid-19 appeared in the United States. The disease is highly infectious, but a large proportion of cases show no or very mild symptoms. Therefore, many people have suffered Covid without knowing it.
Contracting Covid reduces the likelihood of getting it again; it’s a natural vaccine. Walgreen’s isn’t testing two groups, vaccinated and unvaccinated, but three: vaccinated, unvaccinated who have already had Covid, and unvaccinated who haven’t. (Many vaccinated have also had Covid, but they don’t enter into this particular discussion.) Walgreen’s doesn’t report, and surely doesn’t know, the relative proportions of the last two groups. Since Covid is easy to contract, it seems likely that, after the causative virus has been in circulation for at least 25 months, a very high percentage of the unvaccinated have, knowingly or not, been infected and have “natural immunity”. What the Walgreen’s chart suggests, then, is that Covid is the best vaccine against itself. Of course, a symptomatic case is rather less pleasant than a jab in the arm.
Second, Walgreen’s isn’t testing a random sample of the public. There are two principal motives for being tested: Covid-like symptoms and compliance with demands to show a negative test as a condition for coming into the office, traveling or other activities. The unvaccinated are required to present test results more often than anyone else. It follows that they are less likely than the vaccinated to be symptomatic at the time of their tests. Someone with symptoms is, in any conceivable set of circumstances, more likely to have Covid than someone without.
The Walgreen’s data indeed show that the unvaccinated account for a considerably larger percentage of tests than their percentage of the whole population. For instance, according to CDC data, 95 percent of persons age 65 and older have been vaccinated, but 13.4 percent of Walgreen’s test takers in that age group haven’t been. In the 45 to 64 age group, the vaccination rate is around 90 percent and the Walgreen’s test percentage 24 percent.
The combination of these factors makes the chart explicable. Many, plausibly a great majority, of the unvaccinated group are naturally immune, and a significant proportion have no symptoms. The vaccinated group is mostly symptomatic, and it is reasonable to think that the more vaccine doses they’ve had, the less likely they are to be tested in the absence of overt symptoms.
In summary, the strongest inference from the Walgreen’s data is that natural immunity to Covid is widespread and effective. Once one takes into account who are being tested and why, the alternative hypothesis, that Covid vaccines cause the illness through some unknown mechanism, is supported only weakly, if at all.