When it comes to tracking health and health behaviour at a population scale, researchers and clinicians need to turn to a different approach – one that is more akin to a collective sensor or intricate web of event records that is able to chart and dynamically adapt measurement to the current challenges of the day – a cohort.

For years, studies like the Children of the 90s and Generation Scotland have been working to generate “sampling frames” to record, track and test relationships between risk factors, health outcomes and interventions that shape our wellbeing.

Until 2020, the driving agents for these investigations included (and still do) social inequality (like access to healthcare, income and working), chronic non-communicable diseases (like heart disease, diabetes, arthritis and cancer) and bridging disorders which sit across different realms such as mental health and psychological disorder. Importantly, the lessons learnt from one cohort can be compared to another and then to the population as a whole.

This year, things have been altered hugely by the arrival of a real and rapidly evolving threat to our lives, COVID-19. However, rather than putting our research on hold while the NHS battled to manage the pandemic, our cohort studies switched to find new ways to understand the full impact of this new, acute and rapidly spreading infection.

Through rapidly assembled and repeated questionnaires across a large number of participants, it has been possible to track the effect of mitigation and enforced behaviour change.  We have seen persistent age-dependents alterations in anxiety and depression across our regional cohorts-. We found alterations to child behaviour, sleep, activity and habits from the indirect effects of COVID-19 on day-to-day lives. We are able to examine patterns of contacts within families and households and the interplay between occupational status, infection and related outcomes such as anxiety, risk perception and worry.

Alongside these questionnaires, in the Children of the 90s we have been able to assess directly the immunological response to COVID-19, tracking cases of disease through to recovery to fill gaps in our knowledge about different individuals respond to infection, develop immunity and are likely to respond to vaccination. Generation Scotland can do this indirectly by linking to the NHS Scotland data that tracks swab and serology (antibody) tests to GP and hospital data.

As we get better at treating hospitalised cases and bring the fatality rate down, so the long-term consequences of milder infection demands greater attention, so-called long COVID-19. Longitudinal population-based studies are ideally placed to support long COVID-19 research, because they have a rich bank of health data and biological samples from beforeand afterthe emergence of disease.

This work is important, exciting, contributory and unique to cohorts. It reflects a rare situation where established infrastructure and effort can immediately respond to the current needs and generate useful results and data almost in real time for policy makers and for teams of collaborating researchers.

An excellent example of cohort  leverage is the Wellcome Trust COVID-19 Questionnaire.

How much does it matter how old you are, where you live, how you live, what you do?  There is growing evidence that they all matter, but to varying extents and in a context dependent manner. The Wellcome Covid-19 secretariat draws on evidence for across the UK in our villages, towns and cities and across the life-course. It feeds directly into the National Core Study and will provide a foundation stone for the Population Research UK initiative.

As we welcome the arrival of not just one, but several very promising vaccines, this is a time for optimism, but also vigilance. There is much left unknown about COVID-19 and the long-term sequelae – on health, wellbeing, human behaviour and socioeconomic factors. These will not simply disappear. The role for longitudinal health research cohorts has never been more important for knowledge gain, human and societal insight, future planning and policy impact.

However, it is our participants who are the unsung heroes of COVID-19 research. Participants in our UK cohorts are extraordinary people. They chose to respond to our invitations to give up time for questionnaires, to give blood and to attend clinics during a national lockdown. Some of our families have given up to fifty years of health research contribution and have risen to the challenge so we can make rapid and detailed responses to the pandemic. From the position of those of us responsible for these studies, we can only offer our thanks – without participants, we would be lost.

It is increasingly the case that sharing of data between cohorts is the only effective way to address questions of such widespread relevance and complexity as COVID-19.  This we see as key to continued and future investment in cohort studies and our duty to all study participants.