Purpose: Many studies report about risk factors associated with adverse changes in mental health during the COVID-19 pandemic while few studies report about protective and buffering factors, especially in older adults. We present an observational study to assess protective and buffering factors against COVID-19 related adverse mental health changes in older adults. Methods: 899 older adults (55 +) in the Netherlands were followed from 2018/19 to two pandemic time points (June–October 2020 and March–August 2021). Questionnaires included exposure to pandemic-related adversities (“COVID-19 exposure”), depressive and anxiety symptoms, loneliness, and pre-pandemic functioning. Linear regression analyses estimated main effects of COVID-19 exposure and protective factors on mental health changes; interaction effects were tested to identify buffering factors. Results: Compared to pre-pandemic, anxiety symptoms, depression symptoms and loneliness increased. A higher score on the COVID-19 adversity index was associated with stronger negative mental health changes. Main effects: internet use and high mastery decreased depressive symptoms; a larger network decreased anxiety symptoms; female gender, larger network size and praying decreased loneliness. COVID-19 vaccination buffered against COVID-19 exposure-induced anxiety and loneliness, a partner buffered against COVID-19 exposure induced loneliness. Conclusion: Exposure to COVID-19 adversity had a cumulative negative impact on mental health. Improving coping, finding meaning, stimulating existing religious and spiritual resources, network interventions and stimulating internet use may enable older adults to maintain mental health during events with large societal impact, yet these factors appear protective regardless of exposure to specific adversities. COVID-19 vaccination had a positive effect on mental health.