Barbara Loe Fisher, president of the National Vaccine Information Center, an advocacy group that questions the safety of vaccines, said the swine flu has “breathed new life” into the cause. “People who have never asked questions before about vaccines are looking at this one,” Ms. Fisher said.

The increased interest is frustrating to health officials, who are struggling to persuade an already wary public to line up for shots and prevent the spread of the pandemic. According to a CBS News poll conducted last week, only 46 percent said they were likely to get the vaccine. The nationwide poll, which has a margin of sampling error of plus or minus three percentage points, found that while 6 in 10 parents were likely to have their children vaccinated, less than half said they were “very likely to.”

“I wonder if the people disseminating this false information about this vaccine realize that what they are doing could result in some people losing their lives,” said Dr. Jonathan E. Fielding, the director of the Department of Public Health for Los Angeles County. The comments of vaccine dissenters, which he said “politically come from the left and the right,” were frequently “not just counterproductive,” he said, “but downright disgraceful.”

Web sites, Twitter feeds, talk radio and even elevator chatter are awash with skeptics criticizing the vaccine, largely with no factual or scientific basis. The most common complaint is that the vaccine has been newly formed and quickly distributed without the benefit of clinical trials; in fact, the swine flu vaccine was made using the same techniques as seasonal flu shots over the last two decades, and a small number of clinical trials were conducted this year to determine the adequate dose.

Image Leslie Wygant Arndt of Portland, Ore., has mixed feelings about having her daughter, Beatrice, get the H1N1 vaccine. Credit... Leah Nash for The New York Times

There are also claims that the vaccine contains adjuvants  sometimes added to make vaccines more effective  although they have not been used in this one. In addition, there is fear that the vaccine could lead to Guillain-Barré syndrome, as was suspected the last time a swine flu vaccine was distributed, in 1976; flu vaccines are now much purer than they were, minimizing the risk, and Guillain-Barré is far rarer.