Original mRNA Vaccines Protect Children From COVID-19-associated ED visits


The CDC reports the original COVID-19 monovalent and bivalent vaccines helped reduce emergency department or urgent care encounters for children aged 6 months to 5 years.

This article appeared originally on our sister website, Contemporary Pediatrics.

In a multisite analysis, complete primary vaccination with the original mRNA COVID-19 vaccines helped protect against COVID-19-associated emergency department (ED) or urgent care (UC) encounters for children aged 6 months to 5 years. Published by the Centers for Disease Control and Prevention’s (CDC) Morbidity and Mortality Weekly Report (MMWR) for August 18, 2023, vaccine effectiveness (VE) data for Pfizer-BioNTech’s and Moderna’s original monovalent vaccines, and updated bivalent vaccines for children 6 months and up were evaluated.1

The original monovalent mRNA vaccines, authorized in June 2022, were based on immunobridging, safety, and limited efficacy data from clinical trials. Authorization of Pfizer-BioNTech’s vaccine was for children aged 6 months to 4 years, while Moderna’s was for children aged 6 months to 5 years. In December 2022, recommendations were expanded to include bivalent vaccines. Investigators stated that data on post-authorization VE are necessary to know how well the vaccines worked, and to help vaccine policy for this age group in the future.1

Since efficacy data were limited, investigators used a multisite, electronic health record-based network called VISION to analyze VE against COVID-19-associated ED or UC encounters. Data included in the VISION network were from 6 sites in 8 states, according to the report. VE was assessed from July 4, 2022, to June 17, 2023, for immunocompetent children aged 6 months to 4 years that received Pfizer-BioNTech’s monovalent 3-dose primary series, and for children aged 6 months to 5 years that received Moderna’s monovalent, 2-dose primary series that visited participating EDs or UCs. Children had to visit these locations with a COVID-19-like illness and had to have received a SARS-CoV-2 nucleic acid amplification test 14 days before or 72 hours after the ED or UC encounter. Children were classified as unvaccinated, vaccinated with 1 or 2 Moderna doses; 1, 2, or 3 monovalent doses of Pfizer-BioNTech’s vaccine; or vaccinated with 1 or more bivalent doses. ED or UC encounters with the most recent vaccine dose received less than 14 days before the index date were excluded. Children that received bivalent doses were only included if they had a complete primary series of monovalent or bivalent dosing.1

A test-negative case-control study design was used to stratify VE. The design compared odds of COVID-19 vaccination vs being unvaccinated for patients that received a positive SARS-CoV-2 test result (case patients) and for those who received a negative test result (control patients).1

A total of 90,905 ED or UC encounters among children aged 6 months to 5 years were eligible for inclusion for the Moderna monovalent, for which 4,934 (5.4%) were case patients and 85,971 (94.6%) were control patients. Another 96 encounters occurred in control patients who received 1 or more bivalent Moderna doses. There were 81,077 ED or UC encounters among children aged 6 months to 4 years who were eligible to be included in the Pfizer-BioNTech monovalent analysis, where 4,642 (5.7%) were case patients and 76,435 (94.3%) were control patients. An additional 222 children with an ED or UC encounter were eligible for analysis, after receiving 1 or more doses of Pfizer-BioNTech bivalent dose. Of these patients, 219 were control.1

All children, no matter the dose or vaccine product received, including those aged 5 years who received a Pfizer-BioNTech dose, were assessed to better understand coverage. Between July 4, 2022, and June 17, 2023, 5,131 case patients were identified, and 340 (6.6%) received 1 or more monovalent doses, while 3 patients (0.06%) received 1 or more bivalent dose, regardless of manufacturer. In the same time frame, of the 92,777 control patients, 11,195 (12.1%) were given 1 or more monovalent dose(s), while 384 children (0.4%) received 1 or more bivalent dose, regardless of manufacturer.1

With 2 monovalent Moderna vaccine doses—a complete primary series—VE for children aged 6 months to 5 years against ED or UC encounters was 29% (95% CI = 12%-14%) at 14 or more days after second dose (median = 100 days after second dose [IQR = 63-155 days]). For children aged 6 months to 4 years, VE of 3 monovalent Pfizer-BioNTech doses (complete primary series) was 43% (95% CI = 17%-61%) at 14 or more days after the third dose (median = 75 days after third dose [IQR = 40-139 days]). The authors also found that “effectiveness of [1 or more] bivalent dose, comparing children with at least a complete primary series and 1 or more bivalent dose to unvaccinated children, irrespective of vaccine manufacturer, was 80%” (95% CI = 42%-96%) for children aged 6 months to 5 years, with a median of 58 days after the dose (IQR = 32-83 days).1

Complete primary vaccination helped protect against ED or UC encounters in young children after analysis of data in the VISION electronic health record. Though few children received a bivalent vaccine dose, it provided 80% protection for those who received a complete primary series compared to unvaccinated children. With a median interval of 58 days since receipt of the bivalent doses, there was “little time for waning to be observed,” the authors noted.1

The study authors concluded all children should be up to date with recommended COVID-19 vaccines and initiate the vaccination process immediately when products become available. They also noted, “the predominantly circulating SARS-CoV-2 variants had evolved substantially from the strain included in the original monovalent COVID-19 vaccines by the time young children became eligible, highlighting the importance of receiving an updated vaccine.”1

Currently, as of April 18, 2023, the original Pfizer-BioNTech and Moderna COVID-19 vaccines are no longer authorized in the United States, and that updated vaccines from these manufacturers are being used for all age groups.2


  1. Effectiveness of monovalent and bivalent mRNA vaccines in preventing COVID-19-associated emergency department and urgent care encounters among children aged 6 months-5 years – VISION Network, United States, July 2022-June 2023. Morbidity and Mortality Weekly Report. August 18, 2023. Accessed August 29, 2023. https://www.cdc.gov/mmwr/volumes/72/wr/mm7233a2.htm?s_cid=mm7233a2_w
  2. COVID-19 vaccines for people wo are moderately or severely immunocompromised. Centers for Disease Control and Prevention. Updated May 31, 2023. Accessed August 29, 2023. https://www.cdc.gov/coronavirus/2019-ncov/vaccines/recommendations/immuno.html#:~:text=Original%20vaccines%2C%20sometimes%20called%20%E2%80%9Cmonovalent%20vaccines%E2%80%9D&text=Novavax%20is%20the%20only%20original,FDA%20in%20the%20United%20States.

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