Background : |
The influenza A viruses are negative-sense, single-stranded, segmented RNA viruses of the genus Alphainfluenzavirus, family Orthomyxoviridae. There are several subtypes, named according to the type of Haemagglutinin (H1-18) and Neuraminidase (N1-11) (Centers for Disease Control and Prevention, 2017). Humans are generally infected by influenza viruses of the subtypes H1, H2 or H3, and N1 or N2. In April 2009, a new virus, referred to as A/(H1N1) pdm09, appeared in Mexico and California (US), and was responsible for the first pandemics of the 21st century (claiming several hundred lives). It spreads rapidly from person to person, and is not related to any circulating inter-pandemic viruses. It is a quadruple reassortant virus, consisting of two swine-origin viruses, one avian-origin virus and one human-origin virus. It has a high fatality rate and shows higher incidence among younger people (Baldo et al., 2016). WHO convenes technical consultations in February and September each year to recommend viruses for inclusion in influenza vaccines for the northern and southern hemisphere influenza seasons, respectively. Between September 2019 and January 2020, influenza activity was reported in all regions, with influenza A(H1N1)pdm09, A(H3N2) and influenza type B viruses co-circulating. WHO has identified four strains as the most likely to circulate in the 2020-2021 influenza season, including Influenza A [A/Hawaii/70/2019 (H1N1)pdm09-like virus. Since December, 2019, coronavirus disease 2019 (COVID-19) has been an international public health emergency and co-infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and other respiratory viruses have been reported, complicating their diagnosis (Azekawa et al., 2020; Cuadrado-Payán et al., 2020; Wu et al., 2020). |