The anti-vax movement has done a lot to derail one of the greatest achievements of modern medicine: vaccinations. Measles, a potentially lethal disease that is easily prevented with the MMR vaccine, has seen a global resurgence this year, with 1,261 cases reported in the US alone. In 2016, that figure was just 86.

Parents opting not to vaccinate their children is a key cause of the virus’ comeback, and one way they have been targeted is through Facebook ads. A new study, published in the journal Vaccine, has found that more than half of anti-vax ads on Facebook come from just two funders: the World Mercury Project (WMP), chaired by Robert F Kennedy Jr., and Stop Mandatory Vaccination (SMV), headed by Larry Cook.

This year, the World Health Organization (WHO) ranked vaccine hesitancy as one of its top 10 threats to global health. A key issue behind an increase in vaccine hesitancy – the refusal to get yourself or your child vaccinated – is the spread of misinformation, which is exacerbated by social media.

The new study examined over 500 vaccination-related adverts shown to Facebook users between December 2018 and February 2019. The researchers noticed that anti-vax ads were generally uniform, mainly focusing on supposed harms of vaccines, and 54 percent were financed by WMP and SMV. Meanwhile, pro-vaccine ads covered a variety of topics, such as the benefits of vaccines, vaccine-related philanthropy, and policy. These ads also came from a more diverse range of buyers – 163 ads were financed by 83 buyers. Anti-vax buyers also tended to have bigger budgets, giving their ads a bigger reach.

An issue faced by those promoting vaccinations and raising awareness of their proven safety is that Facebook classes vaccine ads as “political”. This can cause positive ads to be taken down while tightly organized anti-vaxxers use tactics to get around restrictions, for example by using language such as “freedom” or “choice” instead of directly talking about vaccines.

"By accepting the framing of vaccine opponents – that vaccination is a political topic, rather than one on which there is widespread public agreement and scientific consensus – Facebook perpetuates the false idea that there is even a debate to be had," said David Broniatowski, associate professor of engineering management and systems engineering at George Washington University, and principal investigator of the study, in a statement. "This leads to increased vaccine hesitancy, and ultimately, more epidemics.

"Worse, these policies actually penalize pro-vaccine content since Facebook requires disclosure of funding sources for 'political' ads, but vaccine proponents rarely think of themselves as political. Additionally, vaccine opponents are more organized and more able to make sure that their ads meet these requirements."

Time and time again, science has conclusively shown that vaccines are safe and save millions of lives around the world. Unvaccinated children die of diseases like measles, so purporting the notion that vaccines are dangerous has detrimental consequences.

In March of this year, Facebook announced it was updating its ad policies in an attempt to combat anti-vax advertising. Time will tell whether this proves to be a success.