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To vaccinate 6-month- to 5-year-olds against SARS-CoV-2 or not to vaccinate


A family’s decision to vaccinate their child is best made jointly with a trusted medical provider who knows the child and family. The American Academy of Pediatrics created a toolkit with resources for answering questions about the recently authorized SARS-CoV-2 mRNA vaccines (Pfizer and Moderna) for 6-month- to 5-year-olds with science-backed vaccine facts, including links to other useful AAP information websites, talking points, graphics, and videos.1

Dr. Christopher J. Harrison is professor of pediatrics and pediatric infectious diseases at Children’s Mercy Hospitals and Clinics, Kansas City, Mo.

Dr. Christopher J. Harrison

SARS-CoV-2 seasonality

SARS-CoV-2 is now endemic, not a once-a-year seasonal virus. Seasons (aka surges) will occur whenever a new variant arises (twice yearly since 2020, Omicron BA.4/BA.5 currently), or when enough vaccine holdouts, newborns, and/or those with waning of prior immunity (vaccine or infection induced) accrue.

Emergency use authorization submission data for mRNA vaccine responses in young children2,3

Moderna in 6-month- through 5-year-olds. Two 25-mcg doses given 4-8 weeks apart produced 37.8% (95% confidence interval, 20.9%-51.1%) protection against symptomatic Omicron SARS-CoV-2 infections through 3 months of follow-up. Immunobridging analysis of antibody responses compared to 18- to 25-year-olds (100-mcg doses) showed the children’s responses were noninferior. Thus, the committee inferred that vaccine effectiveness in children should be similar to that in 18- to 25-year-olds. Fever, irritability, or local reaction/pain occurred in two-thirds after the second dose. Grade 3 reactions were noted in less than 5%.

Pfizer in 6-month- through 4-year-olds. Three 3-mcg doses, two doses 3-8 weeks apart and the third dose at least 8 weeks later (median 16 weeks), produced 80.3% (95% CI, 13.9%-96.7%) protection against symptomatic COVID-19 during the 6 weeks after the third dose. Local and systemic reactions occurred in 63.8%; less than 5% had grade 3 reactions (fever in about 3%, irritability in 1.3%, fatigue in 0.8%) mostly after second dose.

Neither duration of follow-up is very long. The Moderna data tell me that a third primary dose would have been better but restarting the trial to evaluate third doses would have delayed Moderna’s EUA another 4-6 months. The three-dose Pfizer data look better but may not have been as good with another 6 weeks of follow-up.

Additional post-EUA data will be collected. Boosters will be needed when immunity from both vaccines wanes (one estimate is about 6 months after the primary series). The Advisory Committee on Immunization Practices noted in their deliberations that vaccine-induced antibody responses are higher and cross-neutralize variants (even Omicron) better than infection-induced immunity.4

Are there downsides to the vaccines? Naysayers question vaccinating children less than 5 years old with reasons containing enough “truth” that they catch people’s attention, for example, “young children don’t get very sick with COVID-19,” “most have been infected already,” “RNA for the spike protein stays in the body for months,” or “myocarditis.” Naysayers can quote references in reputable journals but seem to spin selected data out of context or quote unconfirmed data from the Vaccine Adverse Event Reporting System.

Reasons to vaccinate

  • While children have milder disease than adults, mid-June 2022 surveillance indicated 50 hospitalizations and 1 pediatric death each day from SARS-CoV-2.5
  • Vaccinating young children endows a foundation of vaccine-induced SARS-CoV-2 immunity that is superior to infection-induced immunity.4
  • Long-term effects of large numbers of SARS-CoV-2 particles that enter every organ of a developing child have not been determined.
  • Viral loads are lowered by prior vaccine; fewer viral replications lessen chances for newer variants to arise.
  • Transmission is less in breakthrough infections than infections in the unvaccinated.
  • Thirty percent of 5- to 11-year-olds hospitalized for SARS-CoV-2 had no underlying conditions;6 hospitalization rates in newborn to 4-year-olds have been the highest in the Omicron surge.7
  • No myocarditis or pericarditis episodes have been detected in 6-month- to 11-year-old trials.
  • The AAP and ACIP recommend the mRNA vaccines.

My thoughts are that SARS-CoV-2 vaccine is just another “routine” childhood vaccine that prepares children for healthier futures, pandemic or not, and the vaccines are as safe as other routine vaccines.

And like other pediatric vaccines, it should be no surprise that boosters will be needed, even if no newer variants than Omicron BA.4/BA.5 arise. But we know newer variants will arise and, similar to influenza vaccine, new formulations, perhaps with multiple SARS-CoV-2 strain antigens, will be needed every year or so. Everyone will get SARS-CoV-2 multiple times in their lives no matter how careful they are. So isn’t it good medical practice to establish early the best available foundation for maintaining lifelong SARS-CoV-2 immunity?

To me it is like pertussis. Most pertussis-infected children are sick enough to be hospitalized; very few die. They are miserable with illnesses that take weeks to months to subside. The worst disease usually occurs in unvaccinated young children or those with underlying conditions. Reactogenicity was reduced with acellular vaccine but resulted in less immunogenicity, so we give boosters at intervals that best match waning immunity. Circulating strains can be different than the vaccine strain, so protection against infection is 80%. Finally, even the safest vaccine may very rarely have sequelae. That is why The National Vaccine Injury Compensation Program was created. Yet the benefit-to-harm ratio for children and society favors universal pertussis vaccine use. And we vaccinate even those who have had pertussis because even infection-based immunity is incomplete and protection wanes. If arguments similar to those by SARS-CoV-2 vaccine naysayers were applied to acellular pertussis vaccine, it seems they would argue against pertussis vaccine for young children.

Another major issue has been “safety concerns” about the vaccines’ small amount of mRNA for the spike protein encased in microscopic lipid bubbles injected in the arm or leg. This mRNA is picked up by human cells, and in the cytoplasm (not the nucleus where our DNA resides) produces a limited supply of spike protein that is then picked up by antigen-presenting cells for short-lived distribution (days to 2 weeks at most) to regional lymph nodes where immune-memory processes are jump-started. Contrast that to even asymptomatic SARS-CoV-2 infection where multibillions of virus particles are produced for up to 14 days with access to every bodily organ that contains ACE-2 receptors (they all do). Each virus particle hijacks a human cell producing thousands of mRNA for spike protein (and multiple other SARS-CoV-2 proteins), eventually releasing multibillions of lipid fragments from the ruptured cell. Comparing the amount of these components in the mRNA vaccines to those from infection is like comparing a campfire to the many-thousand-acre wildfire. So, if one is worried about the effects of spike protein and lipid fragments, the limited localized amounts in mRNA vaccines should make one much less concerned than the enormous amounts circulating throughout the body as a result of a SARS-CoV-2 infection.

My take is that children 6-months to 5-years-old deserve SARS-CoV-2–induced vaccine protection and we can and should strongly recommend it as medical providers and child advocates.

Dr. Harrison is professor of pediatrics and pediatric infectious diseases at Children’s Mercy Kansas City (Mo.). Children’s Mercy receives funding from GlaxoSmithKline, Merck, and Pfizer for vaccine research studies on which Dr. Harrison is an investigator. Email him at


1. AAP. 2022 Jun 21. As COVID-19 vaccines become available for children ages 6 months to 4 years, AAP urges families to reach out to pediatricians to ask questions and access vaccine.

2. CDC. Grading of recommendations, assessment, development, and evaluation (GRADE): Moderna COVID-19 vaccine for children aged 6 months–5 years.

3. CDC. ACIP evidence to recommendations for use of Moderna COVID-19 vaccine in children ages 6 months–5 years and Pfizer-BioNTech COVID-19 vaccine in children ages 6 months–4 years under an emergency use authorization.

4. Tang J et al. Nat Commun. 2022;13:2979.

5. Children and COVID-19: State Data Report. 2022 Jun 30.

6. Shi DS et al. MMWR Morb Mortal Wkly Rep. 2022;71:574-81.

7. Marks KJ et al. MMWR Morb Mortal Wkly Rep. 2022;71:429-36.

Other good resources for families are or

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