Advertisers pay to reach groups of people on Facebook which include those interested in "Dr Tenpenny on Vaccines", which refers to anti-vaccine activist Sherri Tenpenny, and "informed consent", which is language that anti-vaccine propagandists have adopted to fight vaccination laws, The Guardian reported on Friday.
On Thursday, California congressman Adam Schiff, the chair of the House Intelligence Committee, in letters to Mark Zuckerberg and Google CEO Sundar Pichai, urged them to take more responsibility for health-related misinformation on their platforms.
"The algorithms which power these services are not designed to distinguish quality information from misinformation or misleading information, and the consequences of that are particularly troubling for public health issues," Schiff wrote.
"I am concerned by the report that Facebook accepts paid advertising that contains deliberate misinformation about vaccines," he added.
In 2017, ProPublica, a US-based non-profit organisation, revealed that the platform included targeting categories for people interested in a number of anti-Semitic phrases, such as "How to burn Jews" or "Jew hater".
While the anti-Semitic categories found by ProPublica were automatically generated and were too small to run effective ad campaigns by themselves, the "vaccine controversies" category contains nearly nine lakh people, and "informed consent" from about 340,000. The Tenpenny category only includes 720 people, which is too few to run a campaign.
Facebook declined to comment on the ad targeting categories, but said it was looking into the issue, The Guardian reported.
"We've taken steps to reduce the distribution of health-related misinformation on Facebook, but we know we have more to do," a Facebook spokesperson said in a statement responding to Schiff's letter.
"We're currently working on additional changes that we'll be announcing soon."