he world has been offered a first ray of hope for a potential Covid-19 vaccine, created by Pfizer and BioNTech. So far, efforts have been focused on the manufacture and deployment of this and many other vaccines. Now that we have our first candidate, attention will turn to uptake. If researchers offer a vaccine, will people volunteer for it? And if they don’t, why not? As the World Health Organization director-general, Tedros Adhanom Ghebreyesus, warned in March, we are not only fighting a pandemic, but also an “infodemic”, a deluge of information – both factual and incorrect. This can generate doubt and vaccine hesitancy, which the WHO listed as one of the top 10 threats to global health in 2019. A recent survey conducted in the UK found that 36% of people were either uncertain or very unlikely to be vaccinated against Covid-19. One theory attributes growing vaccine hesitancy to the rise of misinformation and conspiracy theories emanating from the anti-vaxx movement. In 1840, when the Vaccination Act was introduced in the UK, the now familiar arguments were aired: vaccines cause harm; the alliance between medical science and government is driven by profit; vaccinations are an infringement of basic civil liberties; healthy lifestyles and homeopathic medicines provide better alternatives. In the case of Covid, conspiracy theorists and anti-vaxxers have spread infectious rumours such as the biologically implausible message that the virus is spread by mobile phone towers. Others spun subplots feature Bill Gates implanting digital microchips during vaccinations or intentionally causing the “plandemic”. Others peddle bogus “natural” cures, from which they make a personal profit. Misinformation can spread faster than the virus, making it difficult to identify an actionable path to counter it. The content is often highly engaging, with simple messages that feed on our deepest fears and doubts. Although most people are unlikely to believe that the world is controlled by a reptilian elite, we do respond to information that is sprinkled with truth. Yes, the risk of catching the common cold can be reduced by a healthy diet, so why not Covid too, some might think. The endgame is polarisation, confusion and distrust via the tactic of what the historians Naomi Oreskes and Erik Conway referred to in their 2010 book as “merchandising doubt”. Social media companies are increasingly being held accountable for risking public health and taking measures to halt the spread of disinformation on their platforms. Beyond monitoring and silencing these groups, our strongest weapon is to inoculate the general public against the infodemic by empowering them to spot and report misinformation. But misinformation is not the only driver behind doubt. As researchers such as Heidi Larson have long pointed out, people may be vaccine “hesitant” for reasons such as complacency, inconvenience or a lack of trust and confidence in whether the vaccine is effective or safe. A vaccine that might typically take a decade to create has been developed at high speed, raising questions about how this has been possible and whether it is safe. Scientists and independent regulators have shifted resources to solve this urgent problem, but this needs to be communicated. Others might look at the relatively healthy middle-aged groups in the trials and question how this will translate to elderly people or children. In addition, the Covid-19 vaccine deployment faces an unprecedented degree of uncertainty and complexity that will be exceedingly difficult to communicate. It may take years or months to know the exact duration of immunity resulting from a vaccine, if and when it needs to be repeated or how protective it is across different groups. Moreover, we are not talking about “the vaccine’” but rather many vaccines, each with distinct caveats. Whether the public will accept a vaccine is driven by who is best able to get the message across. Governments and public health authorities are prone to information-heavy, one-directional communications such as the gov.uk sites that wouldn’t necessarily be classified as engaging material. Uptake of the vaccine will mean engaging in dialogue not only online but also locally, with people on the ground who understand their own communities. Messages need to match everyday experience, and be appealing and adaptive. Dialogue will have to address the legitimate fears and concerns of the public, not just react to the extreme claims of anti-vaxxers with fact-heavy material. Without an engaging and persuasive communications plan, the scientific progress made in developing the Pfizer and BioNTech vaccine and those to come will have been for nothing. • Professor Melinda Mills is the director of Leverhulme Centre for Demographic Science, University of Oxford & Nuffield College and author of the British Academy and Royal Society report on vaccine deployment