In a recent study posted to the medRxiv* preprint server, researchers assess the vaccine effectiveness (VE) of the Moderna messenger ribonucleic acid (mRNA)-1273 against symptomatic severe acute syndrome coronavirus 2 (SARS-CoV-2) infection and associated hospitalizations among children between six months and five years of age.
Study: mRNA-1273 vaccine effectiveness against symptomatic SARS-CoV-2 infection and COVID-19-related hospitalization in children aged 6 months to 5 years. Image Credit: Africa Studio / Shutterstock.com
*Important notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
Background
Vaccination is essential to the coronavirus disease 2019 (COVID-19) pandemic mitigation. On July 28, 2022, a two-dose regimen of Moderna’s mRNA-1273 vaccine was made available for the pediatric population of Ontario between six months and five years of age, with a dosing interval of at least eight weeks apart.
Clinical trials have reported 37% effectiveness for mRNA-1273 vaccination against symptomatic COVID-19 among individuals between two to five years of age and 51% for those between six months to less than two years of age during SARS-CoV-2 Omicron variant predominance. However, real-world information on the VE of mRNA-1273 among children between six months and five years of age is limited.
About the study
The current study was conducted between July 28, 2022, and December 31, 2022, and included 4,039 community-residing children between six months to five years of age with reverse transcription-polymerase chain reaction (RT-PCR)-confirmed symptomatic COVID-19, as well as clinical signs and symptoms of the disease.
The study exposure was the receipt of the mRNA-1273 vaccination, as reported in the COVaxON data system, whereas the outcome was RT-PCR-confirmed symptomatic COVID-19 and associated hospitalization.
The team excluded immunocompromised children, those with missing sex, postal code, or birthdate data, those lacking health insurance, Pfizer’s BNT162b2 vaccinees, or those vaccinated for COVID-19 before July 28, 2022. Children who underwent COVID-19 testing within two weeks of receiving their initial vaccination dose and tested positive for COVID-19 90 days before the specimen collection date were also excluded from the study.
Study covariates included age, sex, comorbidities, population health unit area, the status of influenza vaccination, physician visit frequency in the previous year, maternal healthcare service provider status, and 2016 Census information on income-, density-, visible minority-, and non-essential worker-quintiles.
Multivariate logistic regression modeling was performed to determine the odds ratios (ORs) of mRNA-1273 vaccination among COVID-19 cases as compared to controls and estimate VE. Effect modifications were determined by participant age ranging from six months and less than two years and between two and five years, as well as a SARS-CoV-2-positive RT-PCR result 90 days or more before the index date.
Complete mRNA-1273 vaccination effective in children under five
The study cohort comprised 572 test-positive COVID-19 cases and 3,467 controls, representing 14% and 86% of the study population, respectively. COVID-19-positive individuals were more likely to be under one year old and reside in high-density highest households in regions excluding the middle statistical quintile for the visible minority. The mRNA-1273 vaccinations lowered symptomatic COVID-19 cases and associated hospital admissions one week after the second vaccination dose with VE values of 90% and 82%, respectively.
VE against symptomatic COVID-19 was 20% two weeks or more following the initial vaccination and 90% one week or more following the subsequent vaccination. Peak single-dose VE was 68% between two and four weeks following the initial vaccination and subsequently decreased. Only 222 COVID-19-associated hospitalizations were documented, with fewer than ten hospitalizations among pediatric individuals who received one or more mRNA-1273 vaccinations.
VE against COVID-19-associated hospitalizations was 58% two weeks or more after the initial vaccination and 82% one week or more after the subsequent vaccination. There was no heterogeneity in the VE estimates against symptomatic COVID-19 by prior COVID-19 history or age.
Conclusions
Overall, two mRNA-1273 vaccinations initially protected children between six months and five years of age against symptomatic COVID-19 and associated hospitalizations. However, the study findings could be confounded by health-seeking behaviors and have limited generalizability to immunosuppressed children and those without access to COVID-19 testing facilities during the Omicron-dominant period. Further research is needed to evaluate the long-term VE and assess booster dose requirements.
Compared to previous studies conducted in Ontario, VE estimates against symptomatic COVID-19 were similar to those for children between five to 11 years of age following the initial vaccination at 20% and 24% two to four weeks after the initial vaccination, respectively. Higher VE was reported after the subsequent vaccination at 90% and 66% seven days to four weeks after the subsequent vaccination, respectively.
Although COVID-19-related deaths did not occur, VE estimates against COVID-19-related hospital admission or death among children aged five to 11 years were similar to the present study findings at 82% and 79%, respectively, one week or more after the second dose.
*Important notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
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