This project established the items to be included in a core outcome set (COS) for evaluating interventions to prevent transmission of COVID-19 in care homes. The majority of items (n=13) concern clinical improvement and/or survival, with considerable overlap with items on the WHO ordinal scale for clinical improvement . The remainder (n=11) are considered to be intervention-specific. Care homes are diverse, with considerable heterogeneity between layout and care arrangements, residents  and interventions. Consequently, even though this is a setting-specific COS, the relevance and importance of outcomes may differ between homes. Thus highlighting the importance of context assessment at the pre-intervention stage .
The choice and timing of outcome measures for care home-focused research will need to take account of the relevant benefits and harms of (co-)interventions to address different situations (such as a COVID-19 outbreak in the care home), variable vaccination rates and wider community prevalence . For example, high vaccination rates in residents, staff and visitors may enable other infection control measures such as visiting restrictions and isolation and quarantine of residents and staff to be lifted.
A Cochrane review of non‐pharmacological interventions to prevent or reduce transmission of COVID-19 in care homes published after the COS identified a range of primary outcomes used in 22 studies, including infections, hospitalisations and deaths due to COVID‐19, outbreaks in long‐term care facilities, and adverse health effects . Intervention-specific domains included in the Cochrane review, such as surveillance and contact-regulation measures, were not included in our outcomes. The authors found limited reliable evidence on adverse and other unintended consequences of the interventions. They argued that the intrusiveness and burden of some of these interventions on residents living in care homes with higher vaccination rates needed to be measured alongside the evidence of their effectiveness . This COS captures a range of setting-specific measures, but it is still likely that there will need to be researcher discretion in how they are applied and ongoing review as interventions and circumstances change.
Strengths and limitations
In accordance with COS development guidance, consideration was given to the representativeness of the stakeholders included in the study, and the ability of people across the different groups to engage with the consensus process . A range of expertise and perspectives was sought to ensure that the project takes full account of the health and social needs of residents, alongside their emotional wellbeing, and respects residents’ rights and wishes. However, there were challenges around involving care home residents, many of who may lack capacity to consent . This was compounded by care home staff in the consensus group being unable to attend the meeting despite registering to attend. We cannot rule out the possibility that some perceptions of outcome relevance and importance – important components of outcome quality - were not captured by the Delphi process. Participants predominantly responded in relation to older people living in care homes. The applicability of the COS to younger adults with disabilities as a discrete population living in care homes is therefore unclear. The survey was only available online and in English due to the time-limited nature of the study and, common amongst Delphi surveys, there is a potential for attrition bias. Additionally, participants were almost exclusively from the UK.
Whilst not all modified Delphi approaches contain a consensus meeting component, it is now a well-established component . The format and process of the consensus meeting was designed to take account of the potential issues around power and communication and other barriers that may affect participation by some stakeholders . Strategies to minimize the influence of power differentials between different stakeholders during the meeting included ensuring good preparation, anonymous voting, and facilitation during the discussions . However, voting may have been influenced by the stronger voicing of opinions from others during the meeting. The inclusion criteria for the consensus meeting, where the option was to include or exclude with >70% required for inclusion, was different to the Delphi survey and designed to be definitive.
Implications for the use of the COS in practice
A COS represents the minimum that should be measured and reported in trials, although outcomes used in a particular trial may not be restricted to only those in the COS . The outcomes included in this COVID-PCARE COS will require careful thought around the interpretation of domains and items and their definition in order to avoid differential collection of outcomes. For example, presentation and understanding of symptoms of COVID-19 infection (and hence case definitions) have differed between jurisdictions and evolved over the course of the pandemic. Delirium was only included in diagnostic criteria for COVID-19 relatively late in the pandemic, despite being a common presenting feature in care home residents. This means that those using the COS should specify the symptoms being included and take account of our evolving understanding of the condition .
It is also important to recognise that some outcomes such as ‘needing treatment with oxygen’ could be interpreted either as ‘receiving treatment with oxygen’ or ‘having blood oxygen levels low enough to require treatment with oxygen’. Care home residents may deteriorate to the point that oxygen therapy is needed but they may not wish to attend hospital, it might be deemed inappropriate, or they may not be able to access such therapy in their care setting . Others such as ‘COVID-19 infection’ and ‘COVID-19 negative’ relate to differences between detection-based outcomes and clinical or disease-burden outcomes. Several of the outcomes are related, thereby reducing the measurement burden (e.g., COVID-19 and non-COVID-19 related deaths could be considered as one cause-specific mortality outcome). Similarly, intervention-specific outcomes, such as staff knowledge and awareness about vaccines, will only be relevant to those trials which focus on behavioural interventions.
Ensuring COS uptake can be challenging, however, a number of factors can support uptake, including involving future implementers as stakeholders in the development of the COS and developing an implementation plan . The findings from this project will be disseminated through care home research networks, such as NIHR Enabling Research in Care Homes (ENRICH), in order to inform future trials.
Implications for future research
Once a COS has been agreed (the what to measure), the next stage in COS development is to determine how the outcomes included in the set should be defined and measured  using relevant guidance . Following the approach used in the development of this COS, the measures may be applicable across interventions and populations, or relevant only to specific interventions and/or sub-populations of people living in care homes. Any novel disease may require the development of condition- or domain-specific outcome measurement instruments, but there are additional measurement challenges associated with this context. This includes some outcomes having temporal and/or co-diagnostic components, or which require differentiation between the effects of (co-)interventions and COVID-19 itself, for example a decline in cognitive function that is a consequence of the intervention and not due to COVID-19 illness.
Interventions to prevent COVID-19 may also have an impact on infection rates in care homes of other diseases such as influenza. Therefore, as COVID-19 transitions towards endemicity, the COVID-PCARE COS may have relevance beyond outbreaks of COVID-19 and beyond COVID-19 itself. The importance of better preparation for future pandemic research for older people has been highlighted , therefore the rapid response approach used and outcomes identified in this COS will also be relevant to future pandemics.