The reality is that seasonal influenza is associated with 290,000 to 650,000 deaths globally every year. Studies have shown that hospitalisation rate in Singapore is 50.1 per 100,000 person-years, but higher rates are found in young children and the elderly aged over 65 years.
RESPIRATORY ILLNESSES BACK WITH A VENGEANCE
Experts have been warning that common respiratory illnesses could return with a vengeance as pandemic measures are lifted. Strategies, including aggressive testing, travel restrictions, lockdowns and mask wearing, were effective in controlling the transmission of not only the coronavirus but also influenza and other respiratory viruses such as RSV.
The number of influenza cases dramatically dropped during the COVID-19 pandemic, leading to almost zero circulation of human influenza viruses for more than two years. Together with lower rates of influenza vaccination, this likely resulted in waning population immunity, making all of us more susceptible as influenza strains resume global circulation.
Another reason could be due to the dominant H3N2 subtype this time round. The burden of influenza varies from season to season, depending on the prevalent strain. At present, there are four subtypes of influenza viruses circulating among us: Two subtypes of influenza A (H1N1 and H3N2) and two of influenza B (Victoria and Yamagata).
Of the four, H3N2 viruses typically have a faster rate of mutation. Similar to SARS-CoV-2 virus, influenza viruses are RNA viruses that mutate with time and generate new variants.
Like the coronavirus and its spike protein, influenza subtypes are characterised by the hemagglutinin protein (such as H3 in H3N2) which binds to the cell to cause infection. Mutations in this protein can enable the virus to evade our immune system.
This means the H3N2 strain in the influenza vaccine will need to be updated more frequently or risk becoming less effective against the current circulating viruses.