Twitter CEO Jack Dorsey is facing criticism for promoting a fitness writer and podcaster who has spread fears about vaccines. Dorsey tweeted his endorsement of the podcaster, author Ben Greenfield, after appearing on his show, noting that he was grateful for all of the work Greenfield does to “simplify the mountain of research focused on increasing one’s healthspan.” A Twitter spokesperson alleged that Dorsey wasn’t aware of Greenfield’s views on vaccines.

Despite pushback, Dorsey has yet to respond. Twitter has been pointing reporters instead to a follow-up tweet from Greenfield in which he says, “I rarely visit the topic, and had no idea until I did how charged the issue was.” Greenfield now says he is “not against vaccinations” and claims he had his kids vaccinated. But as recently as a month ago he wrote, “Vaccines do indeed cause autism.” There is overwhelming scientific evidence that this is not true and that vaccinations have saved tens of millions of lives.

I am not against vaccinations. They have saved many lives. I was vaccinated. My children were vaccinated. But I also think we need to respectfully pay attention to potential adverse health effects. I rarely visit the topic, and had no idea until I did how charged this issue was. — Ben Greenfield (@bengreenfield) March 13, 2019

Dorsey’s endorsement comes at a time when tech platforms like Amazon, Facebook, and YouTube are similarly facing backlash over the spread of anti-vax conspiracy theories. Amazon has removed some books that spout misinformation, Facebook is closing anti-vax groups, and YouTube is running information boxes about vaccines beneath conspiracy theory videos.

Twitter does have policies that prevent people or companies from running ads that spread misinformation, but there isn’t any rule preventing users from spreading conspiracy theories or false information. So when Greenfield tweeted in February that “vaccines do indeed cause autism” to his audience of more than 70,000 followers, Twitter took no action.

“Dorsey’s endorsement comes at a time when tech platforms like Amazon, Facebook, and YouTube are similarly facing backlash over the spread of anti-vax conspiracy theories.”

This isn’t the first conversation about anti-vax conspiracy theories that has followed a podcast appearance with Dorsey. On comedian Joe Rogan’s podcast earlier this month, Dorsey said that Twitter gives people an opportunity to find information from a variety of perspectives, rather than restricting the spread of information. He added that Twitter hasn’t dealt with misinformation spanning a number of topics, and he didn’t note whether Twitter would start addressing anti-vaccination misinformation.

Twitter’s chief legal counsel, Vijaya Gadde, added that Twitter tries not to “police what’s true and not true.” She also said that Twitter is more focused on combatting misinformation that harms people in “a direct and tangible way.” Spreading misinformation by linking out to YouTube videos or articles promoting anti-vaccination conspiracy theories “is not a violation of Twitter’s rules,” she said.

Dorsey has repeatedly been criticized for tweets that overlook bigger cultural issues. In November 2018, Dorsey was on a trip in India when he posed with a sign that says “Smash Brahminical Patriarchy.” The sign was in reference to the country’s caste system, which is a controversial topic in India. Dorsey didn’t immediately respond to the backlash that occurred online, but a Twitter spokesperson told Bloomberg that Dorsey didn’t know what the sign meant and pleaded ignorant.

Then, just a month later, Dorsey found himself in trouble again after tweeting a lengthy thread about his trip to Myanmar. Although the country is embroiled in civil unrest, Dorsey ignored the country’s problems to tweet about topics like meditation and the positive effects of living a spiritual lifestyle. He failed to note that social media platforms like Facebook have been used to spur actual violence in countries like Myanmar.

Dorsey, after three days of silence, responded to the Myanmar controversy in a Twitter thread where he said he “could have acknowledged that I don’t know enough and need to learn more.” If Dorsey’s past actions here are any indication, we may see the Twitter chief respond on his platform regarding the anti-vax situation in short order.