Governments, public health authorities, and social media platforms have employed various measures to counter misinformation that emerged during the COVID-19 pandemic. The effectiveness of those misinformation interventions is poorly understood. We analyzed fifty papers published between January 1, 2020, and February 24, 2023, to understand which interventions, if any, were helpful in mitigating COVID-19 misinformation. We found evidence supporting accuracy prompts, debunks, media literacy tips, warning labels, and overlays in mitigating either the spread of or belief in COVID-19 misinformation. However, by mapping the different characteristics of each study, we found levels of variation that weaken the current evidence base. For example, only 18 percent of studies included public health-related measures, such as intent to vaccinate, and the misinformation that interventions were tested against ranged considerably from conspiracy theories (vaccines include microchips) to unproven claims (gargling with saltwater prevents COVID-19). To more clearly discern the impact of various interventions and make evidence actionable for public health, the field urgently needs to include more public health experts in intervention design and to develop a health misinformation typology; agreed-upon outcome measures; and more global, more longitudinal, more video-based, and more platform-diverse studies.