Apart from Ms. Powell, others who have spread political misinformation such as Rep. Marjorie Taylor Greene, a Republican of Georgia, as well as far-right websites like ZeroHedge, have begun pushing false vaccine narratives, researchers said. Their efforts have been amplified by a robust network of anti-vaccination activists like Robert F. Kennedy Jr. on platforms including Facebook, YouTube and Twitter.

Among their misleading notions is the idea that the vaccines are delivered with a microchip or bar code to keep track of people, as well as a lie that the vaccines will hurt everyone’s health (the vaccines from Pfizer and Moderna have been proved to be more than 94 percent effective in trials, with minimal side effects). Falsehoods about Bill Gates, the Microsoft co-founder and philanthropist who supports vaccines, have also increased, with rumors that he is responsible for the coronavirus and that he stands to profit from a vaccine, according to data from media insights company Zignal Labs.

The shift shows how political misinformation purveyors are hopping from topic to topic to maintain attention and influence, said Melissa Ryan, chief executive of Card Strategies, a consulting firm that researches disinformation.