Just about all federal actions come with controversy these days, and that's true about a change in how new vaccines are tested. The secretary of health and human services, Robert F. Kennedy Jr., now requires extra trials in which some people get the new medication and others get an inactive substance like saline (saltwater) to test the vaccine's value. "Real science demands both transparency and accountability," says Kennedy's spokesman, who calls the shift "a radical departure from past practices." Critics, noting that Kennedy is a longtime vaccine skeptic, are troubled by the break from letting career scientists at the Food and Drug Administration (FDA) make such decisions.

Some worry that the next yearly round of Covid booster shots won't be ready in the fall, a fear reinforced by this statement from the department spokesman: "Trials from four years ago conducted in people without natural [Covid] immunity no longer suffice. A four-year-old trial is also not a blank check for new vaccines each year without clinical trial data, unlike the flu shot, which has been tried and tested for more than 80 years." The FDA has delayed expected approval of a new Covid injection from a Maryland company called Novavax. The plan for controlled studies of that shot and others raises serious questions because it's considered unethical to keep even a small group of patients from getting effective vaccines against deadly diseases.

Under existing approaches, new vaccines often are tested against what's called a placebo (pronounced pluh·SEE·bow ), like saline or another inert substance, to test their safety and impact. But that's not always needed, according to health experts. The recent shift came days after Kennedy advised parents of newborns to "do your own research" before vaccinating infants and suggested the measles shot is unsafe. "If you want to avoid spreading measles, the best thing you can do is take that vaccine," he said. "But does it also do something else -- cause you seizures or cause neurological or autoimmune disease? We don't know. Nobody can answer that question." Actually, those side effects are rare, studies show. (The largest U.S. measles outbreak in about 25 years has killed two youngsters and one adult in recent months.)

The FDA licenses vaccines after a yearslong process that begins with extensive tests in labs and in animals before human trials, often with thousands of people. Before joining President Donald Trump's Cabinet in February, Kennedy crusaded against vaccines and started a group called Children's Health Defense. He petitioned the FDA to pull the Covid shot off the market in 2021 during a deadly phase of the pandemic. He also urged the agency not to allow its use on children, and has said repeatedly that there could be a link between vaccines and autism – a belief widely rejected by leading specialists.

Pediatrician says: "There are a lot of really bad sources of information that will miseducate you about your [vaccine] choice, and Robert F. Kennedy Jr. is a perfect example of that." – Dr. Paul Offit at Children's Hospital of Philadelphia

Past FDA official says: "Vaccines are required to be extensively studied for safety. . . . Safety is paramount." – Dr. Peter Marks, vaccine division chief until he quit under pressure in March

Harvard researcher says: "Tens of thousands of people can die without protection against Covid." -- Dr. Ofer Levy, FDA vaccine advisory committee member