Extended reporting guidance for vaccine effectiveness studies for variants of concern for COVID-19

Following the initial series of phase III RCTs showing vaccine efficacy against SARS-CoV-2, an increasing number of observational studies evaluating vaccine effectiveness have been published. While recognizing that all observational studies are subject to bias, the data from these studies provide valuable insight into the effectiveness of vaccines in the real world. Unfortunately, large variability in reporting results for vaccine effectiveness studies has made it difficult to pool results, and this problem has only worsened as the variants of concern have emerged.

WHO proposed an adapted STROBE checklist in their publication providing interim guidance on evaluation of post-COVID vaccine effectiveness reports [1]. This checklist recommended COVID-19 vaccine specific elements that should be included in reporting vaccine effectiveness studies. As authors of the ongoing ‘Living Evidence Synthesis for Efficacy and Effectiveness of COVID-19 Vaccines for Variants of Concern’ posted on the COVID-END website bi-weekly, we have reviewed hundreds of these studies since April 2021, and based on our experience, we propose additional points that could help strengthen the reporting of observational VE studies for COVID-19.

STROBE Checklist Element	STROBE Item no.	COVID-19 Vaccine Effectiveness Studies
Study design	4	If the study design is test-negative controlled, provide a statement specifying whether asymptomatic people who underwent testing for other reasons (e.g. travel requirements, surveillance screening in long-term care facilities or health care facilities) were excluded or reported separately.
Setting	5	Describe the dominant circulating variant for the entire study period in the study setting, including statements about when/if it changed over time. Sequencing data are optimal; however, estimates/assumptions based on a relevant peer reviewed publication or public health source or established online surveillance dashboard is the minimum requirement for meaningful data interpretation.
Variables	7	Provide details on the definitions used for socioeconomic status and exposure risk. Provide details on the definition of the non-immune period
Data sources/measurement	8	Report whether databases accessed were specifically developed for collecting data on COVID vaccines and outcomes, and whether individual-level data were available. Report number of days of symptoms prior to enrolment and how symptoms were verified.
Main results	16	Report vaccine- and variant-specific results. This will typically require, as a minimum, stratifying the data by calendar time periods defined according to the dominant variant of concern.
		Report results for participants who were within the non-immune period (e.g. 0 to 14 days of the first dose) separately. Do not include them with unvaccinated participants.
		Report results for people with prior infection separately or include prior infection as a covariate.
Other analyses	17	Report vaccine effectiveness adjusted for prognostic factors for COVID infection, severity of disease, and vaccination, including age, sex, gender, race, ethnicity, socioeconomic factors, occupation/exposure risk (health care worker, long-term care) and chronic medical conditions or state adjustment for specified variables made no difference, and provide details on method of adjustment.

Declaration of Competing Interest

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: The COVID-19 Evidence Network to support Decision-making (COVID-END) is supported by funding from the Government of Canada through the Canadian Institutes of Health Research (CIHR). To help Canadian decision-makers as they respond to unprecedented challenges related to the COVID-19 pandemic, COVID-END in Canada is coordinating rapid evidence responses such as the one on vaccine effectiveness for variants of concern which led us to propose these points for consideration. The opinions, results, and conclusions are those of the evidence-synthesis team that prepared the rapid response, and are independent of the Government of Canada and CIHR. No endorsement by the Government of Canada or CIHR is intended or should be inferred. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.