RESPIRATORY SYNCYTIAL VIRUS IMMUNIZATION COVERAGE AMONG INFANTS THROUGH RECEIPT OF NIRSEVIMAB MONOCLONAL ANTIBODY OR MATERNAL VACCINATION – UNITED STATES, OCTOBER 2023-MARCH 2024

The following information was released by the Centers for Disease Control and Prevention (CDC):

Discussion

This report is the first analysis conducted at CDC to provide population-based estimates of the percentage of infants who were immunized against RSV in numerous U.S. states and to analyze the timing of immunization. IIS data from 33 states and DC found that during the first season after approval of nirsevimab for infants and an RSV vaccine for pregnant women, 28.9% of infants born during October 2023March 2024 were immunized against RSV, either through receipt of nirsevimab or through maternal RSV vaccination. The percentages of infants covered varied widely by state, from 10.8% to 53.1%. Only 38.1% of infants who received nirsevimab received the antibodies within the first week of life (06 days after birth), the optimal timing for maximum protection.

An analysis of data from an internet panel survey conducted by CDC during March 26April 11, 2024, estimated that approximately double the percentage (55.8%) of U.S. infants received protection against RSV through maternal RSV vaccination and nirsevimab during the 202324 season as the percentage estimated in this report (8). Differences between the findings of that study and those in this report might be due to an overestimation of coverage in the survey (from self-selection bias, recall bias, or limited sample size) or an underestimation in IIS-based estimates of infant protection in some states because of jurisdictional policies and variation in reporting by immunization providers that might limit the capture of all immunizations administered. Some RSV immunization providers, including birthing hospitals (those with more than one birth within the previous year or at least one registered maternity bed) and outpatient obstetric health care providers who administer immunizations less frequently, might not participate in their jurisdictional IIS, which might limit the data that were used in this report. Several other recent studies (46,9) also reported higher immunization coverage estimates than those in this report; however, most of those analyses were from a single institution or health care network with targeted interventions to promote RSV immunization. A population-based study in Wisconsin using IIS data reported coverage estimates similar to those in this report (36.2%) (7).

Several factors might have contributed to low RSV immunization coverage during the 202324 respiratory virus season. First, although nirsevimab was recommended in August 2023, supply issues limited its availability in some areas, particularly at the beginning of the season (10). Second, lack of familiarity among patients and providers about nirsevimab for infants and maternal RSV vaccine, as well as the complexity of the related pediatric and maternal recommendations, might have contributed to limited acceptance or delayed administration. Third, cost concerns might have also played a role. Private health insurers are allowed a 1-year grace period before they are required to cover ACIP-recommended vaccines under the Affordable Care Act.*** In addition, because nirsevimab might have been too expensive for some hospitals to include as part of routine newborn care, they might have opted not to stock it. Finally, this report only included immunizations administered during the ACIP-recommended months for most geographic areas (2,3); some doses might have been administered outside those months. Preliminary data from the 202425 respiratory virus season suggest RSV immunization coverage among infants aged