Authored by: Venkat Rao
According to a recent study by the US Centers for Disease Control and Prevention (CDC), COVID-19 vaccination may have reduced 27 million SARS-CoV-2 infections, 1.6 million hospitalization, and 235,000 COVID-19-associated deaths among the US adults. Results of the study and the analytical methodologies applied by the investigators were reported in the last week Journal of the American Medical Association (JAMA) Network Open.
The results of the meta-analysis of infection prevalence and hospitalization data were interpreted as a measure of the impact of vaccination as a public health intervention to the COVID-19 pandemic. For the purposes of study, vaccinated persons were defined as adults aged 18 and above and having received two doses of either Pfizer (mRNA BNT 162b2), or Moderna (mRNA01273) vaccines.
CDC researchers used COVID-19-associated hospitalization data for the study period from December 2020 to September 2021 in chronological order by geographic location and age groups to extrapolate results for the vaccinated groups. The numbers and percentages of SARS-CoV-2 infections and COVID-19-associated hospitalization and deaths were estimated among vaccinated adults in the US. These estimates were then combined with the data on vaccine coverage statistics and an estimate on the effectiveness to determine the risk of infection, hospitalization, and mortality. The extrapolated results on infection and hospitalization outcomes were reported as monthly numbers and percentages of SARS-CoV-2 infections and COVID-19–associated hospitalizations and deaths. The results were interpreted as an estimate of reduction of infections (by 27 million cases), hospitalization (by 1.6 million) and death (by 235,000) among those adults who have been vaccinated in the US.
A serious shortcoming in the study is the focus solely on vaccinated adults without accounting for any reduction in infection and hospitalization and deaths among unvaccinated individuals. This renders the study to just one section of the SARS-CoV-2 infection and COVID-19 disease burden in the US. Also, the study does not account for the vaccination efficacy among partially vaccinated individuals. As a result, the results may have led to an underestimation of the disease burden and a less reliable assessment of the overall prevalence of infection, hospitalization, and deaths in the US. Another key methodological deficiency in this study was the adoption of data from previously reported studies on SARS-CoV-2 infection and COVID-19-associated hospitalization and death with reported deficiencies.
Furthermore, the hospitalization estimates assumed that COVID-19-Associated Hospital Surveillance Network (COVID-NET) captures all patients who were tested for SARS-CoV-2 and had a positive result is not accurate, since not all COVID-19 hospitalization data on COVID-NET are tied to a positive virus test result. This results in a serious underestimation of the disease prevalence and hospitalization data. Finally, the study design is biased on vaccinated individuals alone thereby presenting only a partial representation of the vaccination efficacy (two-dose vaccination), without accounting for marginal benefits among partially vaccinated individuals.