Waning Pfizer COVID-19 Vaccine Effectiveness or Confounding by Indication?

Note that views expressed in this opinion article are the writer’s personal views and not necessarily those of TrialSite.

Dr. Ron Brown – Opinion Editorial

November 17, 2021

Confounding by indication occurs in an observational study when some patients have conditions that indicate a higher need to be prescribed the tested treatment than other patients. This could cause patient response to the treatment to differ based on patient conditions, thus confounding the study results: Confounding by Indication. For example, in a recently published November 2021 Israel study, a group of people with more serious conditions had higher priority to receive the Pfizer COVID-19 vaccine earlier in January and February compared to another group without serious conditions who received the vaccine later in March and April. Outcomes of both groups were then tested in June and July, and the incidence of breakthrough infections was found to be 51% higher in the Early Vaccinees group compared to the Late Vaccinees group, which increased to 126% higher when comparing the earliest vaccinees in January to the latest vaccinees in April: SARS-CoV-2-breakthrough infections to time-from-vaccine.


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