WASHINGTON (AFP) - The problem is persistent: A fully vaccinated public figure catches Covid-19, and social media sites are soon flooded with claims that this proves the shots do not work.
From White House press secretary Jen Psaki, US Supreme Court Justice Brett Kavanaugh and American comedian Chris Rock testing positive to former secretary of state Colin Powell dying of Covid-19 complications, prominent cases have triggered a deluge of inaccurate information online.
So-called breakthrough cases are expected and do not mean the vaccines are ineffective, the United States health authorities say.
But claims that the shots are failing can erode trust and slow uptake efforts, which remain crucial as younger children become eligible for the shots.
"Any time there is a breakthrough case, people who feel very concerned about the efficacy of vaccines see it as yet another reason to reinforce the doubt that's already in their mind," said Mr Andy Carvin, managing editor at the Atlantic Council's Digital Forensic Research Lab, describing the problem as a "weaponisation of doubt".
Ms Psaki announced on Oct 31 that she had Covid-19, crediting the vaccine for the mildness of her illness.
But she was described as "living proof that the vaccine is ineffective" by a Twitter user with more than 12,000 followers - one of a number of people who made such claims on social media.
Similar allegations followed the Powell family's October announcement that the retired four-star general died from complications caused by Covid-19, even though he had a type of cancer that experts say undermines the efficacy of the shots.
Positive tests for Justice Kavanaugh and Mr Rock this year also gave rise to accusations that the shots are not effective.
Addressing the issue of misinformation stemming from breakthrough cases is increasingly important, because as more people get vaccinated, more cases - including severe ones - will occur in the vaccinated population, said Dr Devon Greyson, public health researcher at the University of British Columbia.
"Vaccination is an amazing technology, but it isn't a magic force field," Dr Greyson said.
Dr Yotam Ophir, health and science misinformation expert at the University at Buffalo, State University of New York, said that health communicators need to better set public expectations about the realities of the vaccines, both in terms of their benefits and their limits.
The other issue is that "humans have a tendency to pay a lot of attention to vivid cases".
"We don't really know how to think in numbers and statistics, we usually think in stories and good narratives," he said.
What is not covered by the news is "all the people who got vaccinated and stayed healthy", Dr Ophir said.
Ms Nina Jankowicz, a disinformation specialist at the Wilson Centre, said false claims following Mr Powell's death were "especially disappointing", because a lack of nuance in the media allowed misinformation to bloom.
"A lot of the coverage that I saw, even from some of the most trusted news outlets in our country... didn't include information about Secretary Powell's cancer status," she said.
Dr Carvin said the necessity of context in news coverage is at odds with the breakneck speed and need for brevity in the current media environment.
Deciding which breakthrough cases merit coverage - thus possibly inciting a misinformation storm - "very much becomes a media ethics question", he said, adding that "journalists and media in general have to think creatively about how we go presenting it".
Dr Ophir called for policy-level changes to address health misinformation, saying that "we are basically at the mercy of private corporations like Facebook and Twitter" to manage the problem.
"What we're doing right now is putting out fires," he said.
"That's a losing battle. What we will need to do eventually is to find a more systematic solution."