The congressman asked if "medically inaccurate" media violated Amazon's terms of service, and wanted to know if Amazon accepted paid advertising from the anti-vaccine camp on its platforms. He also wanted to know what if anything Amazon did to fight anti-vaccine misinformation and what it planned to do in the future, such as taking the books out of some search results.

In a response to CNN, Amazon only pointed to existing guidelines saying that the company provided access to a "variety of viewpoints" that could include "objectionable" material, but that it also reserved the right to not sell porn or other content it deemed "inappropriate." There was no clear answer, then. However, there was evidence that the company might have already changed its policies: site visitors found that an anti-vaccination movie referenced in the CNN story both vanished from search results and was no longer available to stream on Prime Video.

There's pressure to do something even if you discount the letter. Pinterest, Facebook and YouTube have all either taken action to discourage anti-vaccination claims or have proposals on the table, leaving Amazon as a glaring exception to the rule. And this isn't the same as muting an unpopular political stance. There's a concern that the online spread of anti-vaccination myths is fostering a threat to public safety, and that companies are indirectly contributing to infection rates if they stay on the sidelines.