Because the politicization of vaccines against Covid-19 has fueled the anti-vaccine movement, contributing to the drop in the number of immunizations against measles, polio and other dangerous diseases.
Parents "are asking if they (the vaccines) are really necessary or if we can give them later," says Jason Terk, a Texas pediatrician and spokesperson for the American Academy of Pediatrics.
"It's not a majority of parents, but we are seeing higher numbers," he adds.
Anti-vaccine social media messages are amplified by conservative political figures as well as overseas campaigns, whose misinformation about vaccines predates the pandemic.
And with declining vaccination rates, there are fears that diseases that were largely eradicated in many parts of the world could reappear.
In the United States, the percentage of children in kindergarten having received the recommended vaccines fell by one point, to 94% in 2020-2021.
"I call it parallel contagion," Terk said.
"It seems to be driven by a hesitation over Covid-19 vaccines and a growing distrust of vaccines and the institutions we have relied on to keep us healthy."
In some states, the changes have been striking, especially at the height of the pandemic.
Researchers found a 47% drop in Texas immunization rates for five-month-old babies and 58% for 16-month-olds between 2019 and 2020.
Members of the Proud Boys protest against compulsory vaccination on November 20, 2021 in New York Yuki IWAMURA AFP / Archives
These researchers wrote in the scientific journal "Vaccine" that these declines resulted from confinements, vaccination exemptions but also from an "aggressive anti-vaccine movement in Texas".
Washington state saw a 13% drop in childhood vaccination rates in 2021 from pre-pandemic levels, and Michigan's toddler vaccination rate fell last year to 69. 9%, the lowest in a decade.
adults too
Rates in adults and adolescents have also fallen for vaccines that protect against diseases such as influenza, hepatitis, measles and tetanus, according to health consultancy Avalere.
This led to about 37 million missed vaccination doses from January 2020 to July 2021 for adults and children aged seven and older, Avalere found.
Social media helped create a coalition of anti-vaccines, libertarians and conservative politicians.
This has been amplified by disinformation actors from Russia and elsewhere, according to David Broniatowski, a professor at George Washington University.
“People have opposed vaccines since vaccines have existed but have become more sophisticated over the past 10 years, and much of this is due to the ability to organize on social media across borders,” said Broniatowski, who studies vaccine misinformation.
For him, if anti-vaccine activists, libertarians and foreign actors do not necessarily coordinate, “they have found a common cause” in opposing the vaccination obligation.
"One of the biggest changes we've seen is that vaccines have gone from a health issue to a civil and political rights issue," he added.
Conspiracy theories have surged during the pandemic, according to a 2021 YouGov poll, which found that 28% of Americans and a significant number of people in other countries say the truth about the harmful effects of vaccines is "deliberately hidden ".
Hundreds of members of the Freedom Convoy demonstrate against compulsory vaccination for Covid-19, July 1, 2022 in Ottawa Dave Chan AFP / Archives
Mr Broniatowski says foreign disinformation agents are using vaccines as a way to "mobilise part of the population".
Research from the Center for European Policy Analysis showed that China and Russia had promoted disinformation about the Covid-19 vaccine, in part to show that Western governments were incompetent and untrustworthy.
“There has been a concerted effort by these actors to undermine the position of science because it serves their political purposes,” Broniatowski said.
The problem is also growing globally.
A United Nations report revealed last year that 23 million children worldwide did not receive routine vaccinations in 2020.
© 2022 AFP