As students around the country start a new school year, providers say childhood immunization rates are too low, in some places, to prevent outbreaks of diseases like measles.

The big picture: After COVID kept kids isolated from classmates and discouraged routine medical visits, experts fear the student population will have lower immunity and be behind on routine vaccines.

Why it matters: Schools and public health officials have to convince parents to get their kids caught up on recommended childhood vaccinations or risk the very real threat of the return of illnesses once mostly eliminated.

• While COVID showed how outbreaks can engulf school-aged children, the pandemic response revealed the drawbacks of school closures to kids' development, making future mitigation efforts open to political blowback.

What we're hearing: Global vaccination rates plummeted during the pandemic and have yet to rebound, leaving more kids and teens vulnerable.

• "If there's an outbreak anywhere in the world, people in the U.S. will be at-risk," Dean Blumberg, chief of infectious disease at the University of California Davis Children's Hospital, told Axios.
• During the 2020-2021 school year, vaccination coverage decreased by one percentage point for U.S. kindergarteners compared to the prior school year, the CDC found, and infant vaccination rates also dropped between 2019 to 2020.

Driving the news: We've already seen out-of-season outbreaks that experts say could have been prevented through regular vaccination.

• Worldwide measles cases increased 79% for the first two months of 2022 compared to 2021.
• New York health officials confirmed the first case of polio in the United States in almost a decade, in Rockland County, where the current polio vaccination rate among two-year-olds is 60.5%, compared to statewide average of 79.1%, per the New York health department.
• In March, a Los Angeles school banquet triggered a flu outbreak so severe that 41% of attendees reported symptoms and administrators closed the school for in-person attendance.

Flashback: Pandemic restrictions and virtual education reduced kids' risk of contracting measles, mumps, rubella and other communicable diseases. And masking, testing and contact tracing tended to keep COVID and other illnesses from spreading through classrooms.

• But the arrival of the more infectious Omicron subvariant underscored how quickly things can change — especially since schools can be breeding grounds for community spread.
• "I think we'll see an increased number of (COVID) cases that come out of schools, and we'll have schools where whole classrooms will test positive which we didn't always see in the past," Sterling Ransone, president of the American Academy of Family Physicians, told Axios.
• Students also likely will bring COVID home to vulnerable family members.
• COVID vaccination rates lag in teenagers and children, and a recent Kaiser Family Foundation survey found more than four in 10 parents will not vaccinate their children under 5 years old against the virus.

Reality check: Politics is fanning anti-vaccine sentiment in the U.S. and around the world, writes Peter Hotez, a vaccine researcher at the Baylor College of Medicine in Nature.

• "Many conservative elected leaders in the U.S. House of Representatives actively promote this health freedom anti-vaccine agenda, as do several U.S. senators, sitting governors and federal judges," Hotez writes. "Far-right extremist groups such as the Proud Boys march at anti-vaccine rallies."
• That sentiment, which has led to at least 200,000 excess COVID deaths in the U.S. that could've been prevented by vaccines, has been amplified in countries across the world, he wrote.

Look ahead: Administrators overseeing routine non-COVID childhood immunizations now will have to overcome more vaccine hesitancy and contend with state laws that allow parents to claim exemptions on religious and moral grounds.

• In 2019, the CDC reported 1,282 measles cases in the United States, the highest number recorded since 1992.
• To protect against measles, 95% or higher herd immunity is necessary, and if vaccination rates dip, especially in local communities or schools, outbreaks are possible.
• Vaccination coverage against measles for kindergarteners nationwide in the 2020-2021 school year was at 93.9%, according to a CDC analysis.
• "Measles outbreaks that occurred pre-pandemic occurred because of travel in people who were under-immunized," Blumberg said.

Bottom line: Pediatricians and family physicians are urging families to remember to vaccinate their children ahead of the school year to keep them safe from outbreaks.

• "There are multiple reasons to vaccinate; it's not just preventing death but also allowing kids to stay in school and thrive and be social and all those things that are vital to a child's development," Gretchen LaSalle, family physician and AAFP Vaccine Science Fellow, told Axios.