News Release

Why we need to talk openly about vaccine side effects

New research from Aarhus BSS at Aarhus University shows that openness about the effectiveness and side effects of vaccines bolster confidence in the health authorities, and this is a crucial factor if we are to defeat the coronavirus pandemic

Peer-Reviewed Publication

Aarhus University

Professor of political science Michael Bang Petersen

image: "When communication about vaccines is not transparent, it triggers uncertainty and people feel they may be misled," says Michael Bang Petersen, professor of political science at Aarhus BSS, Aarhus University. view more 

Credit: Aarhus University

Concerns have been raised about the AstraZeneca and Johnson & Johnson vaccines regarding very rare but potentially fatal side effects related to low blood platelet counts and blood clots. Recently, reports also emerged that the Pfizer-BioNTech vaccine may cause a rare yet serious side effect: heart inflammation. Concerns about side effects may trigger vaccine hesitancy, which the WHO considers one of 'Ten threats to global health'. Securing sufficient acceptance of vaccines is a key challenge in defeating the coronavirus pandemic, both now and in the future.

How can health authorities and politicians help ensure public acceptance of vaccines, which - their rare side effects aside - have proven effective in preventing serious Covid-19 disease? The best way to do this is to talk openly about all aspects of the vaccines including potential negative aspects such as side effects.

"How to communicate about the vaccines is a real dilemma. Politicians have a desire to stop the pandemic as quickly as possible, and this may give them an incentive to tone down the negative sides of the vaccines in order to vaccinate as many people as possible," says Michael Bang Petersen, professor of political science at Aarhus BSS, Aarhus University.

"But our research shows that it does not foster support for vaccination when communication about the vaccines is reassuring, but vague. On the contrary, vague communication weakens people's confidence in the health authorities, and feeds conspiracy theories. When communication is not transparent, it triggers uncertainty and people feel they may be misled," says Michael Bang Petersen.

Together with colleagues from Aarhus BSS at Aarhus University, he has studied the effect of different ways of communicating about vaccines. The study included 13,000 participants, half of them Americans and the other half Danes, and the results have just been published in the widely recognized journal Proceedings of the National Academy of Sciences of the United States of America (PNAS).

Vague communication feeds conspiracies

The results of the study show that open communication fosters support for the vaccines if it transparently describes neutral and positive facts about the vaccines. However, the willingness to be vaccinated declines when the communication is open about negative features of the vaccine.

"Transparency about the negative features of a vaccine creates hesitancy. But this hesitancy is reason-based, and accordingly health authorities still have the possibility of communicating with citizens and explain to them why it may still be advisable to accept the vaccine," says Michael Bang Petersen.

On the other hand, vague or reassuring communication, where negative features of the vaccines are toned down, lowers acceptance of vaccines. The reason is that vague communication creates a sense of hesitancy and uncertainty, and this in turn feeds conspiracy theories and reduces confidence in the health authorities.

Trust is essential

The advantage of open communication - also about the negative features - is that it prevents conspiracy theories from spreading while at the same time boosting trust in the health authorities. According to the researchers, this is key to defeating the coronavirus pandemic.

"Maintaining trust in the health authorities is extremely important because this is the most crucial factor in securing public support for the vaccines. Communicating transparently about vaccines secures the single most important factor for sustaining vaccine acceptance," says Michael Bang Petersen, and he continues:

"Openness ensures long-term trust, and this is crucial if we are to be revaccinated, or in relation to the next major health crisis."

Facts about the research:

  • The new findings are part of a large-scale data-driven research project entitled HOPE - How Democracies Cope with COVID-19 ( The project is financed by the Carlsberg Foundation and headed by Professor Michael Bang Petersen.
  • Method: Pre-registered experimental studies with a total of more than 13,000 participants, half of them Danes and the other half Americans.
  • The research has been published in the article "Transparent communication about negative features of COVID-19 vaccines decreases acceptance but increases trust" in Proceedings of the National Academy of Sciences of the United States of America (PNAS):
  • Authors: Professor Michael Bang Petersen, Postdoc Alexander Bor, Postdoc Frederik Jørgensen and Research Assistant Marie Fly Lindholt from the Department of Political Science at Aarhus BSS, Aarhus University



Michael Bang Petersen, professor of political science, Aarhus BSS, Aarhus University.,
+45 20775944

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