An investigation by The New York Times — involving scores of interviews as well as a review of scholarly papers, news reports, and Russian documents, tweets and TV shows — found that Mr. Putin has spread misinformation on issues of personal health for more than a decade.

His agents have repeatedly planted and spread the idea that viral epidemics — including flu outbreaks, Ebola and now the coronavirus — were sown by American scientists. The disinformers have also sought to undermine faith in the safety of vaccines, a triumph of public health that Mr. Putin himself promotes at home…

“It’s all about seeding lack of trust in government institutions,” Peter Pomerantsev, author of “Nothing Is True and Everything Is Possible,” a 2014 book on Kremlin disinformation, said in an interview.

The Russian president has waged his long campaign by means of open media, secretive trolls and shadowy blogs that regularly cast American health officials as patronizing frauds. Of late, new stealth and sophistication have made his handiwork harder to see, track and fight.