It's been an unusual 2022 influenza season in the southern hemisphere. Early weekly surges in laboratory-confirmed cases and influenza-like illness are exceeding the 5-year average, according to the Australian Government Department of Health and Aged Care.
At the same time, confirmed COVID-19 cases are again on the rise, creating a perfect storm of respiratory viruses that have captured the attention of US virology experts.
The questions on the minds of the US experts are, what can we expect on this side of the globe? and how can public health professionals and clinicians prepare for what portends to be an especially severe season?
"We're seeing there is really a massive increase in cases, and perhaps even more interesting is the fact that these cases are coming at a much earlier time than is normally expected in Australia," Andy Pekosz, PhD, a virologist at the Johns Hopkins Bloomberg School of Public Health in Baltimore, Maryland, told Medscape Medical News. "When we see influenza cases early in winter, that usually means that there [are] a lot of susceptible people…that the immunity from natural infection, which is normally present in the population, is not there anymore," he explained. Unfortunately, the United States is hardly immune to the situation that has been unfolding in Australia.
"In the midst of the COVID situation over the past two years, influenza has been highly unusual; we saw virtually no influenza in 2020," said Wilbur Chen, MD, a professor of medicine at the Center for Vaccine Development and Global Health at the University of Maryland School of Medicine in Baltimore, and a current member of the Advisory Committee on Immunization Practices of the Centers for Disease Control and Prevention (CDC). "We saw [fits] and spurts in 2021, and we're seeing summertime influenza virus circulation in cases being detected, which we don't normally see at all," he told Medscape Medical News. Australia has also been seeing COVID-19 and influenza coinfections, although Pekosz believes that many people are getting infected with one virus or the other.
Still, "the total number of cases of respiratory illness is much, much higher. And you're seeing sort of disease severity from both of these infections, in parallel, going up." Pekosz said he is especially worried about the convergence of influenza and COVID, especially in at-risk populations such as children, older adults, and persons who are immunocompromised. If Australia is a harbinger, clinicians — pediatricians in particular — might want to start preparing for the onslaught of office calls and televisits. Thus far, confirmed, reported influenza rates have been highest in children aged 5-9 years (1847 notifications per 100,000 population), followed by children younger than 5 (1532.7 notifications per 100,000 population), and people aged 10-19 years (1272.2 notifications per 100,000 population). Children and adolescents younger than 16 currently account for more than half (58%) of hospital admissions.
Is This Season's Influenza Vaccine Cocktail a Match?
Vaccine strain matching is not a perfect science; factors such as antigenic properties of the circulating viruses and antigenic drift play important roles, as does naturally waning immunity in older adults (ie, immunosenescence).
Timing is also important; decisions about influenza vaccine components are commonly made earlier in the year and based on the previous season, and are further informed by any specific surveillance data gathered by influenza virologists from the World Health Organization (WHO) and the CDC. Thus far, the majority (82.8%) of laboratory-confirmed Australian influenza cases have been Influenza A (of which 94.6% were unsubtyped), 0.8% A(H1N1) and 4.6% A(H3N2). In their latest report, Australian health authorities stated that it is too early to assess this season's vaccine match and effectiveness.
"It looks like there are a lot of influenza A viruses that are not being further subtyped, although in general, the ones that are being subtyped are H3N2s," Chen said. "Most of them are of a clade that appears to be matching the vaccine strain for the southern hemisphere, and also the planned vaccine for the fall in the northern Hemisphere." "The prospect of vaccination this fall looks like it will be a good match…with the caveat — the ones that are not being typed," he said. Unfortunately, there is no time to wait for the availability of specific typing data. Influenza vaccine rollout has begun, at least from the manufacturing side. This past Monday, Seqirus announced that it had already started to ship its cell-based, adjuvanted, and egg-based vaccines to US healthcare providers.
"Based on the WHO's recommended virus strains for inclusion in influenza vaccines for the 2022-23 Northern Hemisphere season, our Seqirus vaccines in the U.S. include the following strains," the company's chief health officer, Gregg Sylvester, MD, MPH, told Medscape Medical News in an email.
Any opinions, views and beliefs represented in this article are personal and belong solely to the author/s and do not necessarily reflect the opinion, views and beliefs of the organisation and employees of New Image™ International
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