(CNN) As debates abound over whether coronavirus vaccinations should be required in public schools, many experts point out that students already are required to receive several other routine vaccinations to attend childcare or classes in the United States.
"There is an irony because we've had these long-standing mandatory vaccination requirements for schools," Dr. William Moss, executive director of the International Vaccine Access Center at the Johns Hopkins Bloomberg School of Public Health, told CNN on Monday.
But the singling out of coronavirus vaccines seems to be "obviously occurring in a broader social and political context around Covid-19 and the extreme politicization of the disease and vaccines," Moss said. In addition, children are returning to school this year amid the spread of misinformation about coronavirus vaccines.
"I think another factor here is at least a perception that Covid-19 is not a severe disease in children -- and there's no doubt that the risk of severe disease is much lower in children. But it's not zero, and many children have been hospitalized with Covid-19," Moss said. "That's in contrast to the other vaccines, which are really for childhood infectious diseases."
US Centers for Disease Control and Prevention Director Dr. Rochelle Walensky pushed back on the framing that Covid-19 didn't severely impact children in a Senate hearing on Tuesday,
"One thing I just want to note with the children is I think we fall into this flawed thinking of saying that only 400 of these 600,000 deaths from Covid-19 have been in children," she said. "Children are not supposed to die."
According to the National Academy for State Health Policy, five routine childhood vaccines are generally required for children attending childcare or school in all states: diphtheria, pertussis, and tetanus or DTaP for childcare and schools; Haemophilus influenzae type B or Hib for childcare; measles, mumps and rubella or MMR for childcare and schools; polio for childcare and schools and varicella or chickenpox for childcare and schools.
Most school requirements follow the US Centers for Disease Control and Prevention's vaccine schedule for children. The CDC sets adult and childhood immunization schedules based on recommendations from its Advisory Committee on Immunization Practices.
ACIP has recommended use of Covid-19 vaccines in children and teens 12 and older.
While all 50 states have laws requiring specific vaccines for students, there are also exemptions.
All school immunization laws grant exemptions to children for medical reasons. As of April, 44 states and Washington, DC also grant religious exemptions for students and 15 of those states allow philosophical exemptions for children, according to the National Conference of State Legislatures.
For several other vaccines, long-standing requirements in schools can vary state by state. For instance, vaccination against hepatitis B is required in all states except Alabama, whereas an annual flu shot is only required in Connecticut, Massachusetts, New Jersey, New York City, Ohio, Pennsylvania and Rhode Island.
The human papillomavirus, or HPV, vaccine represents an instance where most states have not followed CDC recommendations. The agency recommends the HPV vaccine for adolescents and young adults, but only Washington, DC, and three states -- Hawaii, Rhode Island and Virginia -- require the vaccine for elementary and secondary schools.
There are also differences by states when it comes to coronavirus vaccine mandates in schools. In the US, people 12 and older can get a Covid-19 vaccine, but it is not yet authorized for younger children.
An updated CNN analysis has found that, as of Monday, at least nine states -- Alabama, Arizona, Arkansas, Florida, Indiana, Montana, Ohio, Oklahoma and Utah -- have enacted legislation this year that would restrict public schools and universities from requiring either coronavirus vaccinations or documentation of vaccination status.
Moss described these laws as "tension between public health and individual liberties."
"In many cases, including school vaccination mandates, we say the state has the right to sacrifice some individual liberties for the good of the public, and we do that in many ways -- indoor smoking restrictions, wearing seatbelts -- there are many, many examples where we do this, but the vaccine is just a particularly contentious one," Moss said. "So, I see the prohibition of even asking for documentation as a misguided attempt to preserve individual liberties, but at a tradeoff for public health."
As of June 22, at least 34 states had introduced bills that would limit requiring someone to demonstrate their vaccination status or immunity against Covid-19, according to the National Conference of State Legislatures, which has been tracking legislation related to coronavirus vaccines.
The laws take different approaches, but the result is that some schools can't require coronavirus vaccines, or in some cases, proof of vaccination. For some states, that's the case even as schools still expect students to arrive with other recommended childhood vaccinations, including those against measles, whooping cough, polio and chickenpox.
Alabama's law, for instance, states that "institutions of education may continue to require a student to prove vaccination status as a condition of attendance only for the specific vaccines that were already required by the institution as of January 1, 2021" -- which would not include coronavirus vaccines.
There's also the issue of authorization versus full approval.
In Ohio, the law states that a public school or state institution of higher education shall not "require an individual to receive a vaccine for which the United States Food and Drug Administration has not granted full approval" -- and that includes coronavirus vaccines.
"Covid-19 is a little bit different from these other vaccines because of the way it had to be developed, and so right now we only have an emergency use authorization -- so it's not fully authorized. It hasn't gone through the entire process with the Food and Drug Administration and we don't have years of experience as with other vaccines. That is a difference, I think, in some people's minds who have concerns around potential side effects for children," Hemi Tewarson, executive director of the National Academy for State Health Policy, told CNN on Friday.
"Now the clinical trials for the EUA were robust. Among the children 12 and above obviously there were not significant side effects and it was safe for children to get this vaccine," she added. "But it is in a different approval phase than all these other vaccines that are currently mandated, so that is a distinction."
Currently, three coronavirus vaccines are authorized for emergency use in the United States: two doses of Pfizer/BioNTech for ages 12 and older, two doses of Moderna for ages 18 and older and the one-dose Johnson & Johnson for 18 and older.
Pfizer/BioNTech and Moderna have begun their applications to receive full FDA approval, and Johnson & Johnson has said it intends to file for licensure.
Last week, Pfizer and BioNTech announced that the FDA had granted priority review designation to the companies' application for approval of their Covid-19 vaccine.
But that might be enough to move many Americans. "I don't think just the FDA approval alone is going to be enough for some," Tewarson said.
"For some school districts, they might make a different decision depending on what's happened within your state and community -- but for others, I think there's still going to be the concern that we still don't have years of experience with this vaccine and so you cannot require students to get vaccinated," she said. "What we will have to see is what happens if we start seeing -- and I hope this is not the case -- surges of Covid-19 in schools and communities."
During the pandemic, rates of hospitalization for Covid-19 among adolescents were nearly three times higher than rates of hospitalization for the flu were from the three most recent flu seasons, according to a CDC report published in June. Among those adolescents hospitalized for Covid-19, about a third required intensive care.
In US history, schools developed vaccine requirements in response to seeing outbreaks of infectious and devastating diseases among children, which then could spread from schools to surrounding communities.
"There's a long history of mandatory vaccination requirements for school children in the United States. It actually goes way back to the early and mid 19th century with smallpox vaccination," Moss said. "And the history of mandatory vaccination is paralleled by the same history of anti-vaxxers and people against these mandatory requirements."
The first legal mandate for vaccinations went into place in the United States in the late 19th century when a smallpox epidemic took hold in Massachusetts. The Supreme Court upheld a Massachusetts law in 1905, ruling that the state had authority to enforce vaccination requirements.
At the time, smallpox vaccination was hotly contested, and there were even some anti-vaxxer pamphlets published in 1885 during a smallpox epidemic in Montreal. Smallpox was eradicated in 1979 with a concerted, global vaccination campaign.
Then in the late 1960s and early 1970s there was a renewed focus on vaccinating children in schools because of measles outbreaks.
"In the 1970s schools were a major site of measles transmissions, and the data showed that states with school immunization laws had rates of measles 40% to 50% lower than those without the laws -- and so school vaccine statutes were broadened in the 70s and more strictly enforced," Tewarson said. "So there were vaccine mandates before the 70s but there was a renewed focus when measles outbreaks happened and people saw the difference when there was higher vaccination rates versus not."
In 1977, the US federal government launched a nationwide Childhood Immunization Initiative and "that's really when all 50 states adopted these mandatory school vaccination requirements," Moss said. "That childhood immunization initiative in 1977 was kind of the modern catalyst for this."
Since 2006, the Association of Immunization Managers has had a longstanding position statement on school and childcare immunization requirements, saying that "requirements are effective public health tools for increasing immunization coverage in children, preventing vaccine-preventable disease, and preventing transmission of disease in school and child care settings."