COVID-19 mRNA Vaccines Minimal Effectiveness Against Hospitalization When Studied Over 10 Month Period in Quebec

Sara Carazo, MD, MPH, PhD, Professor of Practice, University of Laval and colleagues from Quebec report on their evaluation of mRNA COVID-19 vaccine effectiveness (VE) for the XBB.1.5 formulation against COVID-19 hospitalizations among adults aged ≥60 years during a ten-month follow-up period. Designing and conducting a test-negative case-control study using Quebec population-based administrative data, the team of physicians and scientists collected specimens from individuals aged ≥60 years tested at an acute-care hospital from October 2023 to August 2024. Such subjects were considered test-positive cases if hospitalized for COVID-19, or controls if test-negative for SARS-CoV-2. Vaccination was defined by receipt of at least one mRNA XBB-vaccine (autumn or spring) dose. Calculating multivariate logistic regression analyses led to an estimated VE relative to several comparator groups, primarily those last vaccinated in 2022, by subvariant predominant period (XBB, JN and KP), by time since XBB-vaccination and by number of XBB-vaccine doses (KP period). The products don’t perform that well. During a ten-month period of follow-up, XBB-vaccinated adults aged 60 years or older had an estimated 30% reduction in their risk of COVID-19 hospitalization. Restricted to the first two months post-vaccination, VE was 55% during the XBB period, 23% during the JN period, and 60% during the KP period, but effectiveness waned over time, with minimal to no protection demonstrated beyond the fourth month, regardless of the subvariant. TrialSite reminds all we are not reporting here on VE against infection, but hospitalization.

The recent study was funded by  Ministère de la santé et des services sociaux du Québe. Note that this study result was uploaded to the preprint server but needs peer review before citing as evidence.

Summary of Findings

The team reports that participants overall, and by XBB, JN and KP periods included: 5532 (4.9%) test-positive cases (1321, 1838 and 1372, respectively) and 108473 (95.1%) test-negative controls (12881, 53414 and 28595, respectively); 14584 specimens were collected during periods of subvariant cocirculation.

By subvariant period, 3322 (25.8%), 27041 (50.6%) and 15401 (53.9%) controls, respectively, were considered XBB-vaccinated.

When measuring against hospitalization the overall vaccine effectiveness (VE) came in at not a great 30% (95%CI:24–35) and by XBB, JN or KP period: 54% (95%CI:46–62), 23% (95%CI:13–32) and 0% (95%CI:-18–15), respectively. During each subvariant period, the hospitalization risk was reduced only during the first four months post-vaccination, again demonstrating the very limited durability of these COVID-19 mRNA countermeasures.

TrialSite Breakdown

During a ten-month period of follow-up, XBB-vaccinated adults aged 60 years or older had an estimated 30% reduction in their risk of COVID-19 hospitalization. Restricted to  the first two months post-vaccination, VE was 55% during the XBB period, 23% during the JN period, and 60% during the KP period, but effectiveness waned over time, with minimal to no protection demonstrated beyond the fourth month, regardless of the subvariant.

Limitations

An observational study, limitations are several. For example, the lack of individual-level genome sequencing could lead to some misclassification in the sublineages-specific estimates, mainly during the KP period where 20% to 30% of analyzed specimens were JN sublineages.

Residual confounding is possible if unmeasured determinants of vaccine-seeking 220 behaviour are associated with COVID-19 testing and hospitalization risk.

VE would be underestimated if individuals with increased immunity due to a recent SARS-CoV-2 infection had delayed or avoided XBB225 vaccination

The authors list several more in the paper.

Lead Research/Investigator

Sara Carazo, MD, MPH, PhD, Professor of Practice, University of Laval

Other authors can be viewed at the source medRxiv