One of the topics we've covered with some frequency over the past few months has been the potential for seeing a `twindemic' of influenza and COVID this winter, now that many people have reduced or abandoned many of the protective measures taken last year for the pandemic.
Although influenza was a no-show over the 2020-2021 flu season, it is now showing some signs of resurgence, along with other winter respiratory viruses (see UK: `Worst Cold Ever' Trending On Social Media).
With hospitals already burdened by COVID cases, the addition of a substantial quantity of flu cases could overwhelm ICUs and Emergency rooms, leading to more `Crisis Standards of Care' being invoked around the country, and the globe.
Added to that are concerns that coinfection with influenza A or B and COVID may produce more severe illness, increase demands on scarce medical resources, and lead to more deaths (see PHE Study: Co-Infection With COVID-19 & Seasonal Influenza).
Although the impact of this winter's COVID/Flu season is impossible to predict, we've already seen many public health agencies issue warnings, including:
To these clarion calls we can add a perspective, which is now in press for China's CCDC Weekly, a Chinese CDC publication modeled after the CDC's MMWR.
Even though they report having COVID under remarkable control in Mainland China, with the prestigious Winter Olympics scheduled for February 2022 in Beijing, they are obviously taking the possibility of a severe winter respiratory season seriously.
Due to its length, I've only posted some excerpts. So follow the link to read the perspective in its entirety.
Perspectives: Public Health Control Measures for the Cocirculation of Influenza and SARS-CoV-2 During Influenza Seasons
John S Tam1,2, , ; Yuelong Shu2,3 View author affiliations
SEASONAL INFLUENZA IN THE MIDST OF COVID-19
The World Health Organization (WHO) named the disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) as coronavirus disease 2019 (COVID-19) and declared the outbreak a Public Health Emergency of International Concern (PHEIC) on January 30, 2020 and a pandemic on March 11, 2020. Globally, there have been 239,437,517 confirmed cases of COVID-19 reported to WHO, including 4,879,235 (2.1%) deaths as of October 15, 2021 (1). The COVID-19 pandemic continues to cause an unparalleled impact on global public health security and economic well-being in the context of previous influenza pandemics as well as other emerging infectious diseases in history (2).
Therefore, it is essential that effective public health control measures are in place for the forthcoming influenza season to protect those at risk (e.g., the elderly and patients with underlying chronic diseases), prevent severe illness, and minimize additional impact on the healthcare system and a surge in hospital admissions.
EPIDEMIOLOGY OF INFLUENZA VIRUSES DURING COVID-19 PANDEMIC
To understand the epidemiology of influenza with an ongoing circulation of SARS-CoV-2, it is essential to understand the general transmission profiles of both competing viruses. The median basic reproduction number (R0) of seasonal influenza was estimated to be 1.28 (4). The estimated R0 of the initial strain of SARS-CoV-2 was reported to be 2.79 (5), which explained the enhanced transmission of SARS-CoV-2 as observed during the early phase of the pandemic as compared to the transmission of seasonal influenza.
The Alpha (B.1.1.7) variant of SARS-CoV-2 emerged in the United Kingdom and was the first variants of concern (VOC) to show enhanced transmissibility (43% to 90% over the ancestral strain in UK) as well as subsequent VOCs (Beta — 50% in South Africa; Gamma — 1.7% to 2.4% in Brazil) (6-7). The Delta (B.1.617.2) variant was first detected in India and showed an estimated R0 of 5.08 (8) and an enhanced transmission rates of 60% over that of the Alpha VOC (6). The Delta variant has replaced the other VOCs, invigorating repeated outbreaks in countries previously able to suppress COVID-19 circulation as well as resurgence of COVID-19 disease in countries with high vaccination coverage (9).
The heightened transmissibility of SARS-CoV-2 will likely affect the spread of respiratory viruses and the epidemiology of influenza in the coming seasons. The differences in transmission profiles of SARS-CoV-2 and influenza may also reflect prior infection and vaccination in previous influenza seasons, conferring a level of population immunity against seasonal influenza, compared with the lack of population immunity to SARS-CoV-2.
Many studies suggested that the decline in the activities of seasonal influenza and other respiratory viruses may have been attributed to the widespread and stringent community non-pharmaceutical intervention (NPI) measures implemented to control the COVID-19 pandemic (10-11,16-17). These included the following:
1) border closure and quarantine of travelers for the control of importation;2) community control measures such as widespread testing, isolating cases, contact tracing, and quarantine of exposed persons;3) physical distancing measures such as stay-at-home orders, cancelling business and social gatherings, and school closures;4) good personal and environmental hygiene including mandatory face mask policies in public areas; and5) campaigns on risk communication to public and community stakeholders.
Many of such measures implemented for COVID-19 control were also suggested to be effective for the control of influenza (18,20-21).In addition to these NPI measures, promotion of influenza vaccination had also been implemented. The increase in influenza vaccine uptake for 2019/2020 and 2020/2021 season was suggested to be a major factor contributing to the reduced burden of influenza of the seasons in Hong Kong. Influenza vaccination statistics in Hong Kong demonstrated 38%, 26%, 24%, and 10% increases in vaccine uptake among children aged 6 months to <6 years, children aged 6 to <12 years, adults aged 50–64 years, and the elderly aged ≥65 years, respectively (22). Similar increase in influenza vaccination rates was also noted in UK for the 2020/2021 season (15).
INCIDENCE AND CLINICAL SIGNIFICANCE OF CO-INFECTION
With the ongoing intense surveillance of pathogens during the COVID-19 pandemic, the recovery of other pathogens in patients with SARS-CoV-2 infection has been reported (23–25). A recent systematic review and meta-analysis on the occurrence of co-infections and superinfections and their outcomes among patients with SARS-CoV-2 infection showed that the pooled prevalence of co-infection amounts to 19% and that of superinfection was 24% in 118 publications included in the systemic review (25). Among viruses identified in the analysis, influenza A had the highest prevalence (22.3%) followed by influenza B (3.8%) among co-infected patients while rhinovirus was the most frequent in patients with superinfection (11%).
It is important to note from the analysis that patients identified with a co-infection or superinfection had higher odds of dying (odds ratio=3.31) than those who had SARS-CoV-2 infection alone. Patients with co-infections had a higher average length of hospital stay than those with superinfections (29.0 days vs. 16 days) and those with superinfections had a higher prevalence of requiring mechanical ventilation (45% vs. 10%) than those with a co-infection. Such information stimulated many discussions about the possible impact of the coming influenza season while variants of SARS-CoV-2 are circulating at the same time (26–29).
As discussed above, influenza infection may induce severe clinical disease due to superinfection or co-infection with SARS-CoV-2 (24). Bai et al. (30) in their research provide the first experimental evidence which may explain the mechanism by which co-infection of influenza virus and SARS-CoV-2 showed enhancement in pathogenesis. It was reported that co-infection was associated with an increased expression level of ACE2, the major receptor for SARS-CoV-2 entry into target cells, leading to the augmentation of SARS-CoV-2 infectivity. It was further observed in another study that simultaneous or sequential co-infection of SARS-CoV-2 and A(H1N1)pdm09 caused more severe disease as compared to single infections by either virus in hamsters (31).
The emergence of SARS-CoV-2 has resulted in an unprecedented global pandemic causing substantial morbidity and mortality, particularly among older and vulnerable adult populations. Public health policymakers worldwide have instituted stringent non-pharmaceutical interventions to mitigation the transmission of SARS-CoV-2 virus. Vaccines for SARS-CoV-2 have been developed and global vaccination for high-risk populations has been implemented gradually. There was concern regarding the potential of increased healthcare burden from the dual impact of an ongoing COVID-19 pandemic coinciding with the seasonal influenza virus peak which may cause significant additional morbidity, mortality, and health-service demand. Experimental and surveillance reports also indicated that co-infection with influenza viruses and SARS-CoV-2 occurs with enhanced severity.
As the 2021–2022 Northern-Hemisphere influenza season approaches, it is important to maintain a high index of suspicion for co-infection. Measures should be adopted to prevent co-infection. Vaccination against influenza becomes even more important. Rapid diagnostic evaluation of patients presenting in respiratory distress to emergency departments for both SARS-CoV-2 and influenza. Treatment with antiviral agents for influenza should be initiated. Moreover, social distancing and mask wearing are beneficial to protect people from the transmission of either or both viruses.
1.Department of Applied Biology and Chemical Technology, Hong Kong Polytechnic University, Hong Kong, China
2.Asia Pacific Alliance for the Control of Influenza (APACI), South Melbourne, VIC, Australia
3.School of Public Health (Shenzhen), Sun Yat-sen University, Guangzhou, Guangdong, China
During a `normal' flu season, influenza kills somewhere between 12,000 and 56,000 people in the United States, which makes the 750,000 deaths from COVID over the past 22 months all the more horrific.
If you haven't gotten the seasonal flu and COVID shots (and appropriate boosters), please know it takes two (or more) weeks for them to take full effect. Getting them before the holidays will improve your chances of avoiding serious illness this winter.
Hopefully we'll get through this winter without seeing the `worst case scenarios' that have inspired these recent public health warnings, but the truth is - by the time we know if it will be bad - it already will be.
And by then, many of our opportunities to blunt its impact will have passed.