New Delhi, Oct 24 : The World Health Organization (WHO) recently advised a reversion to trivalent (three-strain) influenza vaccines for the 2024 southern hemisphere influenza season that typically begins in April. This will likely reshape the global influenza vaccine market for the upcoming seasons, according to a report. The WHO recommendations came amid the influenza season that is underway in the northern hemisphere when vaccination campaigns are in full force. In the UK, the National Health Service (NHS) has delivered its fastest ever rollout of influenza vaccine, with a record 10 million people already vaccinated with quadrivalent (four-strain) vaccines such as AstraZeneca's Fluenz Tetra and Viatris' Influvac Tetra. The WHO recommendations for the northern hemisphere is expected to follow suit. 'The WHO is expected to make the same trivalent composition recommendation for the upcoming influenza seasons in the northern hemisphere. The earliest we can expect to see this changed recommendation would be February 2024, in preparation for the 2024-2025 northern hemisphere influenza season,' Stephanie Kurdach, Infectious Disease Analyst at GlobalData, a data and analytics company, said in a statement. The recommendation to upgrade trivalent vaccines, which provide protection against two strains of influenza A (H1N1 and H3N2) and one strain of influenza B, to quadrivalent vaccines, which also incorporate a second influenza B strain, coincided with the 2012-2013 northern hemisphere influenza season and the 2013 southern hemisphere influenza season. However, one decade later, the WHO is recommending the removal of the B/Yamagata lineage antigen from quadrivalent vaccines, with every effort made to exclude this component as soon as possible, as there have been no confirmed detections of circulating B/Yamagata lineage viruses after March 2020. 'When the actual composition of vaccines will revert to trivalent formulations remains another question. This is no small undertaking for vaccine manufacturers. Estimated transition timelines are expected to vary and could take up to 36-48 months,' Kurdach said. In a recent meeting held by the US Food and Drug Administration (FDA), concerns were cited regarding the proposed composition change included regulatory challenges, manufacturing challenges, and the risk of re-emergence of the B/Yamagata virus lineage. In addition to the challenges faced by the currently marketed influenza vaccines, the proposed composition change will also affect the seasonal influenza vaccine development pipeline. According to GlobalData, the seasonal influenza vaccine pipeline consists of 153 products in active development, and 53 vaccines currently in Phases I-III. Of these, only one is denoted as a trivalent vaccine -- The Institute of Vaccines and Medical Biologicals' IVACFLU-S. IVACFLU-S has been licensed in Vietnam since 2019 but is undergoing additional clinical testing to expand the approved patient populations. 'There is still much uncertainty surrounding the exact course of action needed for vaccine manufacturers to transition and supply trivalent vaccines. Nonetheless, these updated recommendations provide plenty of opportunity for current and future market leaders to re-shape the global influenza vaccine market,' Kurdach said. /IANS