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Background The 2022–23 US influenza season peaked early in fall 2022. Methods Late‐season influenza vaccine effectiveness (VE) against outpatient, laboratory‐confirmed influenza was calculated among participants of the US Influenza VE Network using a test‐negative design. Results Of 2561 participants enrolled from December 12, 2022 to April 30, 2023, 91 laboratory‐confirmed influenza cases primarily had A(H1N1)pdm09 (6B.1A.5a.2a.1) or A(H3N2) (3C.2a1b.2a.2b). Overall, VE was 30% (95% confidence interval −9%, 54%); low late‐season activity precluded estimation for most subgroups. Conclusions 2022–23 late‐season outpatient influenza VE was not statistically significant. Genomic characterization may improve the identification of influenza viruses that circulate postinfluenza peak.

Investigators used a case–control, test-negative design to assess the effectiveness of the BNT162b2 vaccine in adolescents for the prevention of Covid-19–related hospitalization, ICU admission, or receipt of life support. Among 445 case patients and 777 controls, of the 180 patients admitted to an ICU, only 2 had been fully vaccinated; all 7 deaths occurred in unvaccinated patients.

Annual influenza vaccination is recommended for all persons aged ≥6 months in the United States. Interim influenza vaccine effectiveness (VE) was calculated among patients with acute respiratory illness-associated outpatient visits and hospitalizations from four VE networks during the 2024-25 influenza season (October 2024-February 2025). Among children and adolescents aged <18 years, VE against any influenza was 32%, 59%, and 60% in the outpatient setting in three networks, and against influenza-associated hospitalization was 63% and 78% in two networks. Among adults aged ≥18 years, VE in the outpatient setting was 36% and 54% in two networks and was 41% and 55% against hospitalization in two networks. Preliminary estimates indicate that receipt of the 2024-2025 influenza vaccine reduced the likelihood of medically attended influenza and influenza-associated hospitalization. CDC recommends annual receipt of an age-appropriate influenza vaccine by all eligible persons aged ≥6 months as long as influenza viruses continue to circulate locally.

In this study evaluating BNT162b2, vaccine effectiveness against hospitalization for Covid-19 in the delta-predominant period among adolescents 12 to 18 years of age was more than 90%; during the omicron period, vaccine effectiveness was 40% against hospitalization and 79% against critical illness. Vaccine effectiveness against hospitalization was 68% among children 5 to 11 years of age.

In this study, maternal vaccination with an mRNA vaccine during pregnancy was less common among infants hospitalized for Covid-19 than among controls. The effectiveness of maternal vaccination against Covid-19 hospitalization of infants was 52% overall and was greater when delta, rather than omicron, was predominant.

To the Editor: Price and colleagues (published online on March 30 at NEJM.org) 1 describe the effectiveness of the BNT162b2 vaccine (Pfizer–BioNTech) against the B.1.1.529 (omicron) variant of SARS-CoV-2 in children and adolescents, findings that have important clinical relevance and policy implications. However, the study was designed without the inclusion of previous Covid-19 status as a confounding factor. It is well known that SARS-CoV-2 infection confers immune protection and appears to result in increased protection against severe Covid-19, 2 factors that could affect the evaluation of vaccine effectiveness. For instance, the vaccine effectiveness against hospitalization for Covid-19 did not appear to diminish . . .

Multisystem inflammatory syndrome in children (MIS-C) is a severe postinfectious hyperinflammatory condition, which generally occurs 2-6 weeks after a typically mild or asymptomatic infection with SARS-CoV-2, the virus that causes COVID-19 (1-3). In the United States, the BNT162b2 (Pfizer-BioNTech) COVID-19 vaccine is currently authorized for use in children and adolescents aged 5-15 years under an Emergency Use Authorization and is fully licensed by the Food and Drug Administration for persons aged ≥16 years (4). Prelicensure randomized trials in persons aged ≥5 years documented high vaccine efficacy and immunogenicity (5), and real-world studies in persons aged 12-18 years demonstrated high vaccine effectiveness (VE) against severe COVID-19 (6). Recent evidence suggests that COVID-19 vaccination is associated with lower MIS-C incidence among adolescents (7); however, VE of the 2-dose Pfizer-BioNTech regimen against MIS-C has not been evaluated. The effectiveness of 2 doses of Pfizer-BioNTech vaccine received ≥28 days before hospital admission in preventing MIS-C was assessed using a test-negative case-control design among hospitalized patients aged 12-18 years at 24 pediatric hospitals in 20 states** during July 1-December 9, 2021, the period when most MIS-C patients could be temporally linked to SARS-CoV-2 B.1.617.2 (Delta) variant predominance. Patients with MIS-C (case-patients) and two groups of hospitalized controls matched to case-patients were evaluated: test-negative controls had at least one COVID-19-like symptom and negative SARS-CoV-2 reverse transcription-polymerase chain reaction (RT-PCR) or antigen-based assay results, and syndrome-negative controls were hospitalized patients without COVID-19-like illness. Among 102 MIS-C case-patients and 181 hospitalized controls, estimated effectiveness of 2 doses of Pfizer-BioNTech vaccine against MIS-C was 91% (95% CI = 78%-97%). All 38 MIS-C patients requiring life support were unvaccinated. Receipt of 2 doses of the Pfizer-BioNTech vaccine is associated with a high level of protection against MIS-C in persons aged 12-18 years, highlighting the importance of vaccination among all eligible children.

COVID-19 vaccination is recommended for persons who are pregnant, breastfeeding, trying to get pregnant now, or who might become pregnant in the future, to protect them from COVID-19. Infants are at risk for life-threatening complications from COVID-19, including acute respiratory failure (1). Evidence from other vaccine-preventable diseases suggests that maternal immunization can provide protection to infants, especially during the high-risk first 6 months of life, through passive transplacental antibody transfer (2). Recent studies of COVID-19 vaccination during pregnancy suggest the possibility of transplacental transfer of SARS-CoV-2-specific antibodies that might provide protection to infants (3-5); however, no epidemiologic evidence currently exists for the protective benefits of maternal immunization during pregnancy against COVID-19 in infants. The Overcoming COVID-19 network conducted a test-negative, case-control study at 20 pediatric hospitals in 17 states during July 1, 2021-January 17, 2022, to assess effectiveness of maternal completion of a 2-dose primary mRNA COVID-19 vaccination series during pregnancy against COVID-19 hospitalization in infants. Among 379 hospitalized infants aged <6 months (176 with COVID-19 [case-infants] and 203 without COVID-19 [control-infants]), the median age was 2 months, 21% had at least one underlying medical condition, and 22% of case- and control-infants were born premature (<37 weeks gestation). Effectiveness of maternal vaccination during pregnancy against COVID-19 hospitalization in infants aged <6 months was 61% (95% CI = 31%-78%). Completion of a 2-dose mRNA COVID-19 vaccination series during pregnancy might help prevent COVID-19 hospitalization among infants aged <6 months.

Pfizer-BioNTech COVID-19 vaccine is authorized for use in children and adolescents aged 12-15 years and is licensed by the Food and Drug Administration (FDA) for persons aged ≥16 (1). A randomized placebo-controlled trial demonstrated an efficacy of 100% (95% confidence interval [CI] = 75.3%-100%) in preventing outpatient COVID-19 in persons aged 12-15 years (2); however, data among adolescents on vaccine effectiveness (VE) against COVID-19 in real-world settings are limited, especially among hospitalized patients. In early September 2021, U.S. pediatric COVID-19 hospitalizations reached the highest level during the pandemic (3,4). In a test-negative, case-control study at 19 pediatric hospitals in 16 states during June 1-September 30, 2021, the effectiveness of 2 doses of Pfizer-BioNTech vaccine against COVID-19 hospitalization was assessed among children and adolescents aged 12-18 years. Among 464 hospitalized persons aged 12-18 years (179 case-patients and 285 controls), the median age was 15 years, 72% had at least one underlying condition, including obesity, and 68% attended in-person school. Effectiveness of 2 doses of Pfizer-BioNTech vaccine against COVID-19 hospitalization was 93% (95% CI = 83%-97%), during the period when B.1.617.2 (Delta) was the predominant variant. This evaluation demonstrated that 2 doses of Pfizer-BioNTech vaccine are highly effective at preventing COVID-19 hospitalization among persons aged 12-18 years and reinforces the importance of vaccination to protect U.S. youths against severe COVID-19.