To reduce the spread of COVID-19, governments initiated lockdowns, limiting mobility and social interaction of populations. Lockdown is linked to health issues, yet the full impact on health remains unknown, particularly in more vulnerable groups. This study examined impact on frailty and outcomes in high and low COVID-19 risk older adults. We examined health-related behaviours and support resources participants used during lockdown(s). Lockdown impacts in two countries were compared across four time points to examine impacts of different rules. We recruited 70 participants (aged >70 years) in England and Spain. Participants were allocated to higher or lower COVID-19-risk groups based on UK NHS guidelines. They completed assessments for frailty, quality-of-life, loneliness, exercise frequency and social interaction, coping resources and perception of age-friendliness of their environment. The four assessments took place over a 7-month period. Frailty was highest at Time 1 (most severe lockdown restrictions) and significantly higher in the Spanish group. It was lower at Time 3 (lowest restrictions), but did not continue to reduce for the English participants. Perceptions of the age friendliness of the environment matched these changes. Coping resources did not mitigate changes in frailty and outcomes over time, but more frequent physical activity predicted more reduction in frailty. Lockdown had a negative impact on frailty, increasing risk of adverse events for older people, but recovery once lockdowns are eased is evidenced. Further research is required to consider longer term impacts and methods to mitigate effects of lockdown on health.