The simplest explanation for the Delta surge is still the best one

A woman in a mask. Getty Images, iStock
The Delta variant continues its spread across countries all over the globe, including Australia, which was once a poster child for zero-COVID strategies. It's not surprising that anxiety is increasing. Are vaccine efficacy and effectiveness declining so quickly that we will all need booster shots soon? Are younger people more at risk from Delta? Are we all required to return to lockdown? The flip side of anxiety is fatalism. If the vaccine's effectiveness fades so quickly, then why bother getting it?

In times like these, Occam's Razor is a good place to turn for help.

Occam's Razor is often described as a preference to the simplest explanation that matches the facts. However, that can be confusing as the definition of "simple" is not always the case. . Simple. It's simple. The sun rises in the east and sets in the west. The "simplest" explanation is that the sun revolves around the Earth with the moon, stars and earth. To make this simple explanation work, it required more complex add-ons. Copernicus' heliocentric model, in which Earth was one of many planets, didn't fit the facts better. This would have been due to Kepler's refinement and Newton's laws explaining that motion. It was also simpler because it required significantly fewer postulates. You didn't have to create complex epicycles that had no explanation for why the planets moved around the sky as they did.

Today, the number of people suffering from serious illnesses is on the rise among younger people. States like Florida, which have an average level of vaccinations in the United States, are seeing a surge in COVID deaths. Delta is causing a new wave of violence in Israel, which was one of the first countries to immunise its majority population. It is possible that Delta is far more dangerous than the other vaccines, which would explain why it isn't being well protected.

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One thing is certain about Delta: It is more contagious that either Alpha, or the original COVID variant. If we apply Occam's Razor we cannot adopt new postulates such as these without first asking: Does Delta's greater contagiousness adequately explain the observations we have?

It looks as though it may at this point.

Take the Israeli situation. The data suggests a marked decrease in vaccine effectiveness. This could be due to the fact that Delta is successfully evading the immune system, or because vaccines are waning faster than expected. The summary data could be a statistical artifact called a Simpson's Paradox. This is where you have to break down the data into more homogeneous groups to remove the effects of exogenous variables and reveal the truth.

This is a common case with COVID. You need to break down the aggregate results by age. The amalgamated data from Israel shows that approximately the same percentages of vaccinated and non-vaccinated people were suffering from serious illness as COVID. This was evident as of August 7. The effect vanishes when you break it down by age cohort as Alan Salzberg did. Vaccines still work over 90% to prevent serious illness in any given cohort.

How is that possible? The reason the Israeli vaccine uptake is higher in older cohorts than in other countries, such as the U.S., is that the unvaccinated population tends to be much younger. Comparing the unvaccinated to the vaccinated is essentially comparing the elderly and young. Because the elderly are more susceptible to serious illness from COVID, it is easy to see that the rates of serious illness are similar in a younger population who has received less vaccines than an older population. This makes it appear like the vaccines don't work, even though they do. If this analysis is correct, the rise in hospitalizations in Israel could be explained by Delta's extreme contagiousness. A higher number of cases will undoubtedly mean more hospitalizations, and more deaths.

Does this mean that we don't require booster shots? We might need to research the matter further. There is no reason not to seek boosters for the most vulnerable because they are unlikely do any harm. David Leonhardt says that the primary priority should still be to vaccinate the unvaccinated. However, harping about the need for boosters could actually hinder that effort by suggesting vaccines don’t do much good.

COVID data reveals many Simpson's Paradoxes. Florida is a concern because overall Florida vaccination rates are higher than in Mississippi and Alabama. However, the state has not been as badly affected by the Delta wave. Although their similar paths may cause skepticism regarding whether vaccines work, if you break down the data by geography, it is clear that vaccinations have a strong effect. Hospitalizations in Duval County (fully-vaccinated rates: 46.5%) have risen significantly more than in Miami-Dade (full-vaccinated rates: 66.2%).

Demographic breakdowns support the same message. This is evidence that vaccines are effective. The relative rise in younger adults (meaning non-elderly) among those hospitalized and dead is an indication of high vaccine uptake by the elderly. However, even this high uptake, a significant number of elderly Floridians are still not vaccinated. This is especially true in nursing homes where Florida ranks near bottom in the country in terms of staff and residents (73.1%) being vaccinated. Although vaccines work, there are not enough people who are vaccinated to stop a rise in serious diseases and deaths due to the contagious nature of Delta.

This is good news because the vaccines are still available in America. Unfortunately, Occam's Razor requires some statistical sophistication to use correctly. Make sure you properly slice and do not tamper with data. This is a lot to ask of the average citizen. It's reasonable to expect the same from our government officials and media. They should be able see the truth without any alarmism or obfuscation.

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