Different study designs show varying COVID-19 vaccine effectiveness in patients with CKD
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Key takeaways:
- A test-negative observational study design may be best for measuring COVID-19 vaccine effectiveness in patients with chronic kidney disease.
- The cohort design showed the lowest vaccine effectiveness.
Researchers identified a test-negative design as the “least biased and most efficient” to measure COVID-19 vaccine effectiveness in patients with chronic kidney disease, according to data in Kidney International.
Of three designs tested, all showed different vaccine effectiveness among the same patients.
“In observational studies, the [WHO] recommends the test-negative design (TND) to assess coronavirus disease 2019 (COVID-19) vaccine effectiveness, due its accuracy and efficiency,” Kyla L. Naylor, PhD, MES, BHK, adjunct scientist at ICES in Canada, and colleagues wrote. “The vaccine literature suggests that effectiveness estimates in the general population may vary by study design. However, to our knowledge, no studies using the same population and time period have evaluated the impact of study design on COVID-19 vaccine effectiveness estimates in the CKD population, and no study has used the TND.”
In a population-level observational study, researchers used three different study designs to examine vaccine effectiveness among 14,416 patients with stage 5 CKD who had taken a collective of 40,511 COVID-19 tests between Jan. 11, 2021, and Nov. 30, 2021. Data were derived from administrative health care databases at ICES in Ontario, Canada
Study design
In the TND, which was restricted to patients with recorded symptoms, researchers studied 1,202 patients. Of these patients, 74 had tested positive for COVID-19. However, the investigation expanded to a population of 1,348 when exploring severe outcomes, and 220 patients had experienced severe COVID-19 outcomes.
Vaccine effectiveness against COVID-19 after two doses was 67% in this design and 84% against severe outcomes.
In the pseudo-test-negative design (pTND), researchers included 8,127 patients (402 had tested positive for COVID-19) and 7,945 patients for the severe outcome portion (220 had experienced a severe outcome).
Vaccine effectiveness against COVID-19 after two doses was 70% in this design and 84% against severe outcomes.
In the cohort design, researchers examined 14,416 patients. A total of 742 patients tested positive for COVID-19. Of this group, 427 either died or were hospitalized during a median follow-up of 351 days.
Vaccine effectiveness against COVID-19 after two doses was 60% in this design and 72% against severe outcomes. Researchers noted that the estimates for vaccine effectiveness were sensitive to multivariable adjustment in ways that the other designs were not.
Results
“We found several between-study differences in the characteristics of vaccinated vs. unvaccinated individuals and between cases [vs.] controls across study designs,” Naylor and colleagues wrote. “Although we adjusted for most of these characteristics, unmeasured differences could be present that result in differences in vaccine effectiveness estimates across study designs. These differences also highlight how different designs, even within a single population, may produce different study populations, which could affect vaccine effectiveness estimates, interpretability and generalizability of results.”
Of the three designs tested, the TND was the least biased and most efficient to determine vaccine effectiveness. Researchers attributed this to the differences in health care-seeking behaviors and how TND is used in the general population. However, TND requires recorded symptom information, which may not always be available and could make this design inconvenient.
The cohort design showed the lowest vaccine effectiveness measures.
“[A]lthough vaccine effectiveness estimates varied across study designs in the CKD population, overall conclusions were consistent,” Naylor and colleagues wrote. “Results suggest that the pTND might be suitable to estimate vaccine effectiveness in the CKD population. Our results highlight the need for clinicians and policymakers to cautiously interpret vaccine effectiveness estimates from observational study designs, with considerations for potential biases that could impact vaccine effectiveness.”
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