Throughout the COVID-19 pandemic, media and policymakers openly speculated about the number of immune citizens needed to reach a herd immunity threshold. What are the effects of such numerical goals on the willingness to vaccinate? In a large representative sample (N = 1540) of unvaccinated Swedish citizens, we find that giving a low (60%) compared to a high (90%) threshold has direct effects on beliefs about reaching herd immunity and beliefs about how many others that will get vaccinated. Presenting the high threshold makes people believe that herd immunity is harder to reach (on average about half a step on a seven-point scale), compared to the low threshold. Yet at the same time, people also believe that a higher number of the population will get vaccinated (on average about 3.3% more of the population). Since these beliefs affect willingness to vaccinate in opposite directions, some individuals are encouraged and others discouraged depending on the threshold presented. Specifically, in mediation analysis, the high threshold indirectly increases vaccination willingness through the belief that many others will get vaccinated (B = 0.027, p = 0.003). At the same time, the high threshold also decreases vaccination willingness through the belief that the threshold goal is less attainable (B = −0.053, p < 0.001) compared to the low threshold condition. This has consequences for ongoing COVID-19 vaccination and future vaccination campaigns. One message may not fit all, as different groups can be encouraged or discouraged from vaccination.

在整个 COVID-19 大流行期间，媒体和政策制定者公开推测达到群体免疫阈值所需的免疫公民数量。这些数字目标对接种疫苗的意愿有何影响？在一个大的代表性样本（N = 1540) 未接种疫苗的瑞典公民，我们发现，与高 (90%) 阈值相比，给予低阈值 (60%) 对实现群体免疫的信念和对有多少其他人将接种疫苗的信念产生直接影响。与低阈值相比，提出高阈值使人们认为群体免疫更难达到（在七分制中平均大约半步）。然而与此同时，人们也相信会有更多的人接种疫苗（平均多出约 3.3% 的人口）。由于这些信念会影响相反方向的疫苗接种意愿，​​因此根据提出的阈值，鼓励一些人，而另一些人则不鼓励。具体来说，在中介分析中，B  = 0.027，p  = 0.003）。同时，高阈值也降低了疫苗接种意愿，​​因为 与低阈值条件相比，阈值目标更难以实现（ B  = -0.053，p < 0.001）。这会对正在进行的 COVID-19 疫苗接种和未来的疫苗接种活动产生影响。一条信息可能不适合所有人，因为可以鼓励或不鼓励不同的群体接种疫苗。