On September 8, 2022, Havers et al reported that COVID vaccines reduced the risk of hospitalization:
“In this cross-sectional study of US adults hospitalized with COVID-19, unvaccinated adults were more likely to be hospitalized compared with vaccinated adults …”
Moreover, the monthly hospitalization rates during the trial period from January 1, 2021 to April 30, 2022 were reportedly 3.5 to 17.7 times higher in those without compared to those with vaccination.
The trial seemingly confirmed statements from public health officials on the efficacy of COVID vaccination against severe disease. In an interview in August, 2021, for example, the Director of the Center for Disease Control and Prevention stated:
“Our vaccines are working exceptionally well… They continue to work well for delta, with regard to severe illness and death – they prevent it. But what they can't do anymore is prevent transmission.”
However, the Havers et al publication raises questions about the efficacy of COVID vaccination against severe disease. The specifics of the trial are the following. 13,043 patients hospitalized for all causes, who tested positive for COVID-19 were sampled from cases in the COVID-NET hospital network. All medical records were reviewed by the study group and each case was classified according to the “reason for admission”.
Broadly, each case was considered to be hospitalized either “for COVID” or “with COVID”; severe COVID or incidental COVID. The two categories of cases were distinguished according to the criteria:
“… patients admitted for reasons that were likely unrelated to COVID-19 illness were excluded [from the “for COVID” group]”
From Supplementary Table 3, the categorization of the cases by vaccination status and by disease severity is summarized in the table below. In this table, admissions with an incidental positive COVID test are referred to as non-severe disease.
What is notable is that there is only a minimal difference in the unvaccinated-to-vaccinated ratio between the severe COVID and the non-severe COVID groups. The ratio is 6.0 in the Severe COVID group vs. 5.3 in the Non-Severe COVID group. This corresponds to an increase of 18% in vaccine efficacy against severe disease as compared to the vaccine efficacy against infection.
This outcome raises the possibility is that vaccine efficacy is over-estimated. The methodology used in the determination of vaccination status has not been disclosed in this article or publications cited in this article. As described elsewhere, determination of vaccination status in the United States can be problematic. Specifically, there is typically incomplete linking of the medical records with the immunization records leading to misclassification of vaccinated cases as being unvaccinated. Misclassification of this type always produce an upward bias in the estimation of vaccine efficacy.
Great critique. I was wondering about that point of vacc. efficacy against severe desease seemingly supported by studies. If there are other central studies on this Your critique would be likewise much appreciated