Another dot in the blogosphere?

Numbers are the start, not the end

Posted on: March 22, 2021


Video source

This video is timely given the misleading way some people use the efficacy numbers of different COVID-19 vaccines.

The efficacy of the a vaccine is not the same as its effectiveness. I recommend this NYT article for an explanation of how something like “95%” efficacy is derived.

Vaccine trial efficacy is not the same as real use effectiveness. A trial use of the vaccine includes a placebo for one sampled group of people and the vaccine for another group. Actual use only includes the vaccine and is applied across a much larger group of people.

The J&J vaccine trials were also conducted in South Africa and Brazil. Vox video (https://www.youtube.com/watch?v=K3odScka55A) on why the vaccine efficacy numbers cannot be compared.

The J&J trials were also conducted outside the USA — in South Africa and Brazil.

The J&J vaccine trial was conducted over a more severe infection period. Vox video (https://www.youtube.com/watch?v=K3odScka55A) on why the vaccine efficacy numbers cannot be compared.

The J&J vaccine trial was conducted over a more severe infection period.

Back to the video — it explains why efficacy numbers cannot be compared. For example, the Moderna trial was only in the USA. The Johnson & Johnson (J&J) trial also included countries outside the USA (Brazil and South Africa) where variants of SARS-CoV-2 emerged. It was also conducted over a more severe infection period compared to the Pfizer/BioNTech and Moderna trials.

Here is something the video did not point out. The Pfizer/BioNTech and Moderna vaccines have high efficacies after two doses. The J&J vaccine is a single-dose shot.

Screenshot of the range of outcomes after vaccination. From Vox video (https://www.youtube.com/watch?v=K3odScka55A) on why the vaccine efficacy numbers cannot be compared.

The range of outcomes after vaccination.

The video also highlighted that all the vaccines are not designed to absolutely prevent COVID-19 symptoms. If after vaccination people got mild to moderate symptoms, the vaccine is considered effective.

During the trials, all the vaccines mentioned in the video prevented hospitalisation and death among sampled participants. By that measure, all the vaccines were just as good. If we focus only on trial efficacy numbers, we lose sight of this more important outcome.

One general takeaway that applies in any problem-solving and policy-making is this: Numbers are a start, but they are not the end. The explanations and narratives that accompany them provide depth, nuance, and exceptions. If we do not go beyond the numbers, we risk misinforming ourselves and others.

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