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BOSTON – Children who received mRNA COVID-19 vaccines were up to 48% less likely to develop post-COVID conditions (PCCs) following infection, a CDC researcher reported here.

The prospective case-control observational study was conducted during the Omicron wave, and found that mRNA vaccination reduced the likelihood of developing at least one PCC symptom by 34%, and two or more symptoms by 48%. The vaccines also cut the risk of a respiratory PCC by 47%, according to Anna Yousaf, MD, of the CDC Severe Respiratory Illness and Multisystem Inflammatory Syndrome Team in Atlanta.

"These data support COVID-19 vaccination for children and were presented at [CDC's] Advisory Committee on Immunization Practices meeting and taken into consideration when recommending boosters for COVID in children," Yousaf said during a late-breaking abstract session at the IDWeek annual meeting. "They may also be used to encourage increased pediatric vaccine uptake in a population that typically does not experience serious COVID-19 consequences."

While COVID-19 is typically a milder illness in children, an estimated 1-3% will develop PCCs, including abdominal pain or chest pain; cough and dyspnea; depression or anxiety; difficulty concentrating; fatigue and exertional malaise; and acute pulmonary embolism and renal failure, as well as cardiovascular complications like dysrhythmias, cardiomyopathy, myocarditis, and coagulation disorders.

These can cross multiple organ systems and take on a relapsing/remitting nature, Yousaf noted. "They are likely not one condition, but represent many potentially overlapping entities, likely with different biological causes and different sets of risk factors and outcomes."

Even though a low proportion of children develop PCCs, the volume of childhood COVID-19 infections suggests that these post-infective syndromes may be much more common than currently realized, she added.

" of PCC prevalence in children were highly variable, with 5-40% reporting at least one persistent symptom for more than 1 to 3 months after initial infection. A meta-analysis of more recent studies estimates that up to 3% of children have one or more PCCs after COVID-19 illness. And since CDC estimates that over 65 million U.S. children have had SARS-CoV-2 infection, there may be thousands of children with PCCs," Yousaf said.

At least two recent studies suggest that the approved mRNA vaccines help reduce the risk of PCCs in adults, but pediatric data are limited. Yousaf and colleagues enrolled 622 children, ages 5-17 years, at four U.S. sites. They had lab-confirmed infections with an Omicron variant of SARS-CoV-2. The children (or caregivers) completed a PCC survey at least 60 days after diagnosis. Children were enrolled beginning in July 2021 and followed through the summer of 2023. Children were considered vaccinated if they had completed a primary series with an mRNA vaccine at least 14 days before the infection.

The survey asked about new or ongoing symptoms that lasted at least a month after their illness. If they reported symptoms, they were asked about the duration and how much the symptoms affected their daily lives.

Symptoms were grouped into categories including respiratory, such as shortness of breath, runny nose/nasal congestion, and cough; general (fever, unexplained weight loss or weight gain, fatigue); neurologic, including "brain fog," nerve problems, or hearing loss or ears ringing; cardiac (palpitations, chest pain/tightness); gastrointestinal (changes in appetite, nausea, vomiting, abdominal pain); and other, such as joint pain or swelling, rash, bruising/bleeding easily, or bladder problems.

The mean age of the children was 10 years; 474 were vaccinated and 148 were not. There were 28 cases of PCC: 16 in the vaccinated group (3.3%) and 12 in the unvaccinated group (8.1%). Of the cases, 21 (10 vaccinated and 11 unvaccinated) had two or more PCC symptoms.

Respiratory symptoms were common, occurring in 19 cases (nine vaccinated and 10 unvaccinated). Non-respiratory symptoms occurred in 24 cases (14 and 10, respectively).

Children with Black race/ethnicity were more likely to develop PCC, representing 18% of cases and 2% of controls (P<0.01), as were children with lower baseline health status, representing 25% of cases but just 9% of controls (P=0.01).

The final model adjusted for sex, age, number of symptoms during infection, self-reported baseline health and the time between infection and survey completion. In this calculation, vaccination reduced the risk of having at least one PCC symptom with an adjusted OR of 0.66 (95% CI 0.43-0.99) and two or more PCC symptoms with an aOR of 0.52 (95% CI 0.32-0.83). Vaccination also reduced the risk of a respiratory PCC with an aOR of 0.53 (95% CI 0.32-0.86).

Study limitations included the risk of recall bias, and the fact that the sample was predominantly non-Hispanic white (57-60%) which limits generalizability, the authors noted.

Correction: This article was updated to reflect that the Advisory Committee on Immunization Practices is an advisory group for the CDC.

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