Vaccine effectiveness
Over at angrybearblog.com, Peter Dorman asks “what does vaccine effectiveness mean.”
This question is on the minds of those who are vaccinated and those contemplating vaccination, as well as physicians, vaccine developers, the CDC and government officials. Dorman writes: “ The everyday use of “effectiveness” is effectiveness against the virus. The research use is effectiveness relative to the control group. This is immense, but widely misunderstood and seldom explained.”
Yes, effectiveness in drug, device and vaccine trials is measured by comparing control/placebo group results to treatment group results. In the particular case of the COVID-19 vaccines, the trials are not challenge trials. It would be unethical to infect subjects with a potentially lethal virus like SARS-CoV-2. So the idea was that both groups would have some significant likelihood of natural infection that would be reportable in the trial (Disclosure: I’m in the Moderna Phase III trial).
Of course, we know that measured by the standards of their trials, the Moderna, Pfizer, J&J and AstraZenica vaccines all were “effective.” Since then, we have data from millions of vaccinated and unvaccinated people to back up that conclusion and it appears that the Pfizer vaccine will receive full FDA approval in September.
With the inevitable appearance of viral variants, the pressing question is how “effective” are the vaccines against each variant. The frontline assay has been to test antisera from vaccinated people for its ability to block virus from entering cells in culture. By that assay, all the vaccines have been deemed “effective,” albeit with somewhat lower effectiveness than for the original virus in some cases.
As Dorman acknowledges, one assay for vaccine “effectiveness” in the wild is whether it protects from infection. The problem with this is that most COVID-19 infections in both vaccinated and unvaccinated folks are inapparent, and those people are seldom tested, so we really don’t know what either the numerator or denominator are in those effectiveness calculations. More reliable are the statistics on hospitalization and deaths, and there, the performance of vaccines so far have been impressive.
Here’s an article from Nature that summarizes the current state of play. While the dominant theme is uncertainty, the data support the view that the vaccines are helping and that, until new vaccines are available, the best thing to fight new variants is for everyone to be vaccinated.
https://www.nature.com/articles/d41586-021-02054-z?WT.ec_id=NATURE-20210805&utm_source=nature_etoc&utm_medium=email&utm_campaign=20210805&sap-outbound-id=F8C7DC5800EB4926D8285EFA8E73396624E272C1
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