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Some health experts are concerned about the low COVID-19 vaccination rates among children under 5 years old. mixetto/Getty Images

Children as young as 6 months are now eligible to be vaccinated against COVID-19 in the United States.

However, vaccination rates for children of all ages have lagged behind what public health officials had hoped.

About 60% of children ages 12 to 17 are now fully vaccinated. However, only about 30 percent of children from 5 to 11 years of age are fully vaccinated.

Now, there are concerns that the rate could be even lower for children ages 6 months to 4 years.

Only about 3% of children in this age group had received at least one dose of the vaccine as of July 20.

In addition, a recent survey by the Kaiser Family Foundation reports that 40% of parents of children under 5 years old say they will “definitely not” get their child vaccinated against COVID-19. Another 20% said they would “wait and see” how well the vaccine works before getting their children immunized.

Another survey indicated that about 50% of parents intend to get their preschool children vaccinated at some point, although only 20 percent plan to do so within the child’s first 3 months of eligibility.

Healthline spoke to two infectious disease experts about the consequences of not having the youngest members of society vaccinated against COVID-19.

Dr. Monica Gandhi, MPH, is a professor of medicine at the University of California San Francisco.

Dr. William Schaffner is a professor of preventive medicine at Vanderbilt University in Tennessee.

We began our question-and-answer session with the fact an estimated 75 percent of children have already contracted COVID-19 at some point and may have some immunity.

Schaffner: The most common hesitancy I’ve heard from parents is that COVID is less severe in children than in adults. Of course, that is correct but only partially correct. COVID in children may be less severe, but it is not harmless. Consider that [many] children in the U.S. have required hospitalization for COVID and that half of them were previously healthy children without any underlying illness… Not to mention the risk of long COVID and the multisystem inflammatory syndrome that can occur after the recovery from COVID. Clearly, COVID is not harmless and that is why the American Academy of Pediatrics urges all parents to vaccinate all their children.

Gandhi: Study after study at this point in the pandemic, especially with the Omicron variant, shows that “hybrid immunity” or infection followed by a vaccination (or vaccination followed by infection) is stronger than either infection or vaccination alone in preventing further infections. The strength of hybrid immunity has been demonstrated in children as well as in adults. Therefore, even if children have already contracted COVID, getting at least one dose of the COVID-19 vaccine will strengthen their immune response to last for a longer period and protect them from symptomatic infection.

Schaffner: Previous infection with COVID can confer some protection, but it is partial and wanes rapidly. Furthermore, we cannot easily identify children who have had a previous asymptomatic or mild infection. The most secure way to protect your child from severe COVID is to vaccinate them.

I already have been asked how we can make our schools as low risk as possible when they reopen later this summer. The answer is clear: do all we can to make sure that all the children and all the adults are vaccinated.

Gandhi: Both the Pfizer 3-dose vaccine series and the Moderna two-dose vaccine series for children under 5 years of age were effective in generating neutralizing antibodies against COVID-19. The production of antibodies indicates that cellular immunity is likely generated since B cells produce antibodies aided by T cells. Although the confidence intervals in the clinical trials of each vaccine were wide, the Pfizer vaccine protected children from symptomatic infection by ~80% and the Moderna vaccine protected children by ~37%; the latter had a higher rate of side effects than Pfizer. There were no cases of severe illness in either pediatric trial (in either the vaccine arm or the control arm) which is not surprising since young children are not at major risk of severe disease with SARS-CoV-2.

Schaffner: COVID vaccine effectiveness against disease serious enough to require hospitalization is about 85% in young children. This is comparable to the vaccine’s effectiveness in adults.

Gandhi: The health implications are that vaccines generate cellular immunity which lasts a long time and protects individuals from severe disease with COVID-19. Although children may not be at risk for severe disease when very young, they grow up and we often give vaccines early on in life with the hope that they will provide long-lasting protection as the child ages. Moreover, COVID-19, even in its mild form, is very disruptive to work and school due to current isolation requirements, so getting children vaccinated and reducing symptomatic infections can help families and communities.

Schaffner: Unvaccinated children run the risk of becoming ill with COVID which could take them out of school or even require them to be hospitalized. I hope that, as parents take their children to their doctors in preparation for the onset of school, they will speak with their doctors and be reassured that COVID vaccination is the best way to protect their precious children.