Vaccine misinformation on social media has strong effects on behaviour, and the evidence base for interventions to reduce these effects is limited, but better approaches to evidence generation are possible, say Kai Ruggeri and colleagues
Effective population level vaccination campaigns are fundamental to public health.123 Counter campaigns, which are as old as the first vaccines,4 disrupt uptake and can threaten public health globally.4 In 2019, public health researchers linked increases in measles cases with the proliferation of global anti-vaccine campaigns.5 Some of these campaigns originated offline but were later amplified and expedited through social media, resulting in real world harms.6 Though crises and genuine safety concerns can also lower vaccine uptake,78 the return of measles after aggressive anti-vaccine campaigns prompted the World Health Organisation to list vaccine hesitancy among the greatest threats to global health (box 1).14
Box 1 ### Vaccine hesitancy
Here, we use the term “vaccine hesitancy” as originally defined by WHO9: a “delay in acceptance or refusal of vaccination despite availability of vaccination services.” This definition, plus the expanded description of variation based on time, place, and population, gives a broad understanding but also allows us to distinguish vaccination behaviour from the underpinning psychological, environmental, and structural aspects influencing behaviour. This definition is most commonly used in literature pre-dating covid-19. Though there are debates about the most appropriate … RETURN TO TEXT