What can we expect for influenza in the upcoming winter?
With few COVID-19 cases in Australia, there will not be viral competition to stop influenza spreading here. There is evidence of public fatigue with masking and public health restrictions elsewhere – the increased time needed to control the fourth wave of COVID-19 in Hong Kong, for example, was attributed to fatigue and decreased public compliance with recommended infection control measures.9 Australia cannot continue to rely on strong adoption of public health messages by the populace to keep case numbers of influenza suppressed.
So, will we get an influenza outbreak of significance this winter? Would perhaps the arrival of influenza B or the H1N1 strain of influenza A infecting children who are back at school and in childcare centres lead to high community activity?
Some early data suggests that this will not happen. Overseas arrivals spend 14 days in isolation and would not be infectious with influenza or other respiratory viruses when released. Nor are we seeing influenza cases in the north of Australia, which is often an early clue to what will happen across the rest of the country.
Against this was the unusual resurgence of RSV cases in many states during the summer months. In Western Australia, the speed and magnitude of this increase was greater than the usual winter surge.10 One contributing factor may have been reduced immunity to RSV through an increase in the number of RSV-naïve children and possibly a waning RSV immunity in older children related to the delayed season. If there is reduced immunity to influenza due to the absent 2020 season and the virus arrives, influenza activity this winter may be high.
Although the extent of the upcoming influenza season is unknown, we face the risk that community apathy about influenza will reduce the benefit we had last year of very high coverage with influenza vaccines. We cannot allow ‘likely low case numbers’ to cause the loss of recent gains. The three-month interval in the two-dose regimen of the AstraZeneca COVID-19 vaccine leaves a lot of time for influenza immunisation. We must ensure that older people receive the adjuvanted vaccine and that we continue to improve vaccine uptake in children.
Each year our influenza vaccine armamentarium improves. This year we will again have adjuvanted vaccines for the elderly population. In addition, quadrivalent cell-based vaccines are available for the first time this year on the private market for people over 9 years of age. During the production of cell-based vaccines, the virus is grown in cultured cells of mammalian origin (instead of hens’ eggs). These vaccines will have improved effectiveness compared with egg-based vaccines in a year when there is ‘egg adaptation’ during production (i.e. when a strain that is growing poorly adapts to grow more efficiently in the egg environment but thereby changes from the original viral strain that is probably circulating).11
A strong influenza vaccination effort by primary care physicians and other healthcare providers – coupled with closed external borders – should ensure that neither COVID-19 nor influenza case numbers are a cause for concern this winter. RMT