Distinguishing between the COVID-19 pandemic and influenza pandemics (A/H1N1, A/H2N2, A/H3N2): a narrative review

Abstract The COVID-19 pandemic is frequently compared to historical influenza outbreaks, yet this analogy often obscures fundamental biological and epidemiological divergences. As the global health community confronts new threats like H5N1 avian influenza, a rigorous retrospective analysis is essential to distinguish the unique trajectory of SARS-CoV-2 from the influenza pandemics of 1957 (H2N2), 1968 (H3N2), and 2009 (H1N1). This narrative review, adhering to best-practice guidance, synthesises literature published up to mid-2025. We performed targeted searches of PubMed, EMBASE, and WHO/CDC archives to compare SARS-CoV-2 critically and Influenza A across virological, clinical, and sociopolitical dimensions. Our analysis reveals that while both pathogens share respiratory transmission, they differ starkly in evolutionary mechanisms and systemic impact. Virologically, SARS-CoV-2 utilises convergent evolution and broad ACE2 tropism to cause multi-organ pathology and long-term sequelae (Long COVID), distinguishing it from the primarily respiratory effects and reassortment-driven shifts of influenza. Epidemiologically, SARS-CoV-2 exhibits a significantly higher basic reproduction number (R 0 ), rising from ~ 2.5 to > 9.5 in Omicron variants, and substantial asymptomatic transmission, necessitating non-pharmaceutical interventions of unprecedented scale compared to the modest measures of past flu pandemics. The public health response also highlighted a divergence in medical innovation: the development of mRNA vaccines within 11 months represented a “quantum leap” in vaccinology compared to the slower, egg-based timelines of 2009. In conclusion, COVID-19 represents a distinct biological and societal entity that defies the historical “flu template.” The transition to endemicity, marked by year-round waves of immune-evasive variants like JN.1, and the current emergence of mammalian H5N1 underscore the need for pathogen-agnostic preparedness. Future global health security depends on leveraging the genomic and technological assets developed during COVID-19 to counter threats that transcend historical expectations.