Conspiracy theories often involve topics of uncertainty and ambivalence. One of those topics during the Covid-19 pandemic was the vaccination based on the new method using messenger RNA. In a preregistered study with N = 382 participants, we tested an intervention addressing the uncertainty concerning this new vaccination at a time when conspiracy theories about the vaccination method were not yet widely spread. Participants either only read short facts about the new vaccination (no explanation condition), or read these facts in addition to an explanation about the function of messenger RNA vaccines (relevant explanation condition), or they read the facts after the explanation of an alternative issue (irrelevant explanation condition). Results showed that individuals reading the relevant explanations addressing uncertainties surrounding the new vaccination method were less likely to agree with a Covid-19 vaccination conspiracy theory and were more willing to get a Covid-19 vaccination compared to the other conditions. An exploratory analysis showed that agreement with the Covid-19 vaccination conspiracy theory mediated the effect of explanation type on vaccination intentions. Potential implications and limitations are discussed.