The effectiveness of the seasonal flu vaccine towards hospitalization amongst high-risk teams in the course of the 2024 seasonal flu season in 5 Southern Hemisphere nations was low (35%), down from 50% in 2023 however not outdoors the anticipated vary, which can portend related efficacy in the course of the upcoming Northern Hemisphere flu season if related A(H3N2) viruses predominate, Facilities for Illness Management and Prevention (CDC) researchers report.
The interim estimates, revealed late final week in Morbidity and Mortality Weekly Report (MMWR), come from Argentina, Brazil, Chile, Paraguay, and Uruguay, the place a median of solely 21.3% of sufferers hospitalized for flu from March to July 2024 (the Southern Hemisphere flu season) had acquired the flu vaccine.
“Whereas Southern Hemisphere knowledge can’t predict precisely what is going to occur within the Northern Hemisphere, what we will say is that if we see related influenza viruses (strains or clades) circulating this season within the Northern Hemisphere, we will count on related vaccine effectiveness towards influenza-related hospitalizations,” lead writer Erica Zeno, PhD, epidemic intelligence service officer with the CDC’s Influenza Division, informed CIDRAP Information in an e-mail.
This flu season, america is utilizing trivalent (three-strain) vaccines with the identical parts as these in Southern Hemisphere vaccines, Zeno mentioned.
On August 29, the CDC forecasted that the upcoming flu season “shall be just like or decrease than that of the 2023-2024 season price of 8.9 weekly laboratory-confirmed hospitalizations per 100,000, with reasonable confidence,” it wrote. “Nonetheless, previous seasons have various broadly within the variety of sicknesses, hospitalizations, and deaths, relying on the subtypes circulating, inhabitants immunity to completely different subtypes, and vaccine effectiveness towards circulating subtypes.”
Marketing campaign focused high-risk teams
The researchers used a test-negative, case-control design to investigate knowledge from a multinational surveillance community to generate estimates of interim vaccine effectiveness (VE) towards hospitalization with flu-related extreme acute respiratory sickness (SARI).
The examine inhabitants was made up of 11,751 SARI sufferers from three Pan American Well being Group (PAHO) vaccination goal teams: younger kids (58.3%), older kids and folks with underlying medical circumstances (14.5%), and older adults (27.2%). Case-patients had SARI and examined optimistic for flu, whereas management sufferers had SARI and examined detrimental for flu and COVID-19.
Information have been pooled from 30 hospitals in Argentina, 2,477 in Brazil, 13 in Chile, 5 in Paraguay, and 10 in Uruguay starting 2 weeks after every nation’s flu vaccination marketing campaign. Vaccination standing was confirmed utilizing nationwide digital vaccination data.
All nations used World Well being Group (WHO)–beneficial egg-based Southern Hemisphere formulations. Argentina, Brazil, Chile, and Uruguay used trivalent (three-strain) vaccines containing antigens from A/Victoria/4897/2022 (H1N1)pdm09–like virus, A/Thailand/8/2022 (H3N2)–like virus, and B/Austria/1359417/2021 (B/Victoria lineage)–like virus, whereas Paraguay used quadrivalent (four-strain) vaccines that additionally contained the B/Yamagata lineage–like virus.
Vaccination price decrease than prepandemic norms
The 5 nations reported 11,751 flu-related SARI instances and a median low seasonal flu vaccination price. “The documented influenza vaccination protection ranges (21.3%) have been beneath pre–COVID-19 norms,” the researchers wrote. “This discovering is in step with postpandemic declines in vaccination protection throughout the Americas related to vaccine misinformation, hesitancy, and disruptions in routine immunization companies, prevalent in the course of the COVID-19 pandemic.”
