Healthcare providers, epidemiologists and the public are full of questions about the upcoming respiratory season, such as:
- Can we expect a strong resurgence of respiratory ailments, such as influenza, following two years of relatively low activity due to COVID-19 precautions? Has “herd immunity” to flu eroded over the past two years?
- If COVID-19 incidence remains low in the 2022-2023 respiratory season, will other respiratory diseases flourish in its absence? On the other hand, would a resurgence lead to a “multidemic” of COVID-19 and other respiratory diseases, as some have suggested?
- What can developments in the Southern Hemisphere tell us about the upcoming respiratory season?
- What can we expect from respiratory syncytial virus this season? (Last fall and winter, incidence of RSV among adults was higher than normal.)
Questions aside, it’s a safe bet that the 2022-2023 season won’t be anything like the past two.
A year ago
During the 2021–22 season, peak percentage of positive influenza test results from clinical laboratories in the U.S. was the lowest in at least 25 years preceding the COVID-19 pandemic, and the rate of influenza-associated hospitalizations was lower than that in all but the 2011–2012 season.1 The estimate of symptomatic illnesses, medical visits, hospitalizations and deaths caused by influenza virus infection was also lower than estimates for any of the 10 influenza seasons preceding the pandemic.
That’s good news. But what about the upcoming season?
Health experts in the U.S. are warning the nation to prepare for what could be an exceptionally severe flu season this fall and winter.2 One reason is that coronavirus restrictions, such as wearing masks and maintaining physical distance, have fallen out of favor, and people are more likely to encounter the flu virus than they did the prior two years.
The second reason is the decline in “herd immunity.” In a normal year, widespread exposure to the influenza virus generates some community immunity. But fewer people were exposed in 2020 and 2021, resulting in a decline in natural immunity. For example, pediatric flu deaths normally exceeded 100 every year before the pandemic. But the past two flu seasons saw reported pediatric flu deaths fall under 40, with only one pediatric death confirmed in 2020. Lower population immunity means that people are at a higher risk of contracting the flu.
Clues from the Southern Hemisphere
The Southern Hemisphere offers a preview of what might occur in the Northern Hemisphere this season.
Countries in the Southern Hemisphere experienced a tough flu season this winter.2 Australia experienced its worst season in five years, with the rate of cases peaking earlier than usual. In 2020 and 2021, the Australian Department of Health and Aged Care noted a lower rate of reported flu cases and severity, with only 37 laboratory-confirmed flu–associated deaths reported in 2020 and none reported in 2021. There were 600 cases of laboratory-confirmed influenza in Australia in 2021. But in its most recent flu season, the country reported more than 217,000 cases.
In New Zealand, weekly hospitalization rates for flu in the current season were 93% higher, and considerably higher than during the notoriously difficult winters of 2015 and 2017.3 Both New Zealand and Australia saw a resurgence in rhinoviruses (culprits of the common cold), RSV, Human Metapneumovirus (HPMV) and adenoviruses.
As it has in the last two respiratory seasons, COVID-19 is the “wild card” in the 2022-2023 season. Some experts believe the Northern Hemisphere should brace themselves for a COVID-heavy winter, as vaccine and infection-triggered immunity continues to wane. In New Zealand, at the peak of the 2022 flu season, COVID-19 cases were down to 177 per 100,000, a decrease from an Omicron high of 431 per 100,000. Still, the coronavirus was a sizeable cause of pressure on providers.3
In early October the UK Health Security Agency reported increased COVID-19 activity.4 The number of acute respiratory infection incidents (suspected outbreaks) increased in England in week 38 of 2022 to 170 compared to 133 in the previous week. The hospital admission rate for week 38 was 7.62 per 100,000 population, an increase from 4.96 in the previous week.
"In the coming weeks, we expect a double threat of low immunity and widely circulating flu and COVID-19, creating an unpredictable winter and additional pressure on health services,” said Mary Ramsay, head of immunization, Public Health England. “While COVID-19 and flu can be mild infections for many, we must not forget that they can cause severe illness or even death for those most vulnerable in our communities.”
The message remains unchanged
Despite the unknowns, the message for flu and Covid-19 prevention is the same as it has ever been: Get vaccinated to reduce the likelihood of serious illness.3 Even with waning immunity, in New Zealand, the unvaccinated were five times more likely to be hospitalized with COVID-19 than those who received a full dose. Meanwhile, those vaccinated against the flu were more than 50% less likely to develop a fever and cough than the unvaccinated.
Getting a flu shot may seem like common sense to providers, but some patients may need more coaxing than usual this season. The experience of those in the Southern Hemisphere provides a glimpse. For example, in New Zealand, despite the data, the rate of vaccination against influenza was markedly lower this season than it was in 2020, suggesting trends of vaccine fatigue.3 Health providers may have to work harder to get ahead of the potential problem by encouraging vaccination and mask wearing well-ahead of the start of flu season.
In addition to boosters and vaccinations, common sense should prevail. “If you are unwell this winter, please try to stay at home and avoid contact with vulnerable people – this will help stop infections spreading,” said Ramsay.4
Given the mixture of respiratory illnesses expected this season, diagnostic testing remains critical. With Sekisui Diagnostics’ Acucy® Influenza A&B Test, clinicians can test and provide fast and accurate results that aid in the treatment of a patient in one office visit, enhancing the patient experience, reducing the spread of infection and improving patient care. In addition, the Sekisui Diagnostics OSOM® Ultra Plus Flu A and B Rapid Test is an in vitro rapid qualitative test that detects influenza type A and type B nucleoprotein antigens directly from nasal swab and nasopharyngeal swab specimens obtained from patients with signs and symptoms of respiratory infection.
- Influenza Activity and Composition of the 2022–23 Influenza Vaccine — United States, 2021–22 Season, Centers for Disease Control and Prevention
- Nation warned to brace for a difficult flu season, The Hill
- What the Northern Hemisphere can learn from this year’s Australasian flu season, Advisory Board
- National flu and COVID-19 surveillance reports published, UK Health Security Agency