What to Expect With Influenza in the Era of COVID-19

Here are some insights into this upcoming 2021-2022 influenza season as well as concerns of the twindemic and addressing both the seasonal and pandemic viruses simultaneously.

The influenza season of 2020-2021 wasn’t much of a season. In fact, the feared twindemic of co-circulating flu and COVID-19 last season actually never was. So, with such an unusual preceding year, along with all other COVID-related surprises, what can we really say about flu season 2021-2022?

Influenza season usually takes place during winter months for both southern and northern hemispheres. In the United States, flu season peaks during January and February, while in the southern hemisphere it is generally June through August. For the 2020 season, influenza activity has been negligible throughout the world (as has been reported by the World Health Organization (WHO) FluNet1 (data provided by National Influenza Centers (NICs) of the Global Influenza Surveillance and Response System (GISRS)2 and has actually been at the interseason levels since early 2020 (beginning of COVID pandemic). The exact reason for atypical influenza is difficult to define and is likely multifactorial due to COVID-related mitigation strategies, including: universal masking, social distancing, many people working from home, significantly reduced and restricted international travel, and at least suggested possibility of “viral interference” between SARS-COV-2 and Influenza viruses.

As has been the practice in the past, the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO ) continue ongoing monitoring of influenza activity, and release their findings in weekly reports. 3,4 As per the most recent report, influenza activity worldwide remains very low at < 10% positivity of tested specimens. In the southern hemisphere, influenza activity also remains at the interseasonal level, with the majority of influenza virus that has been detected worldwide being influenza B. There is currently ongoing reported influenza activity in Southeast Asia, but still at low levels.

During the 2020-2021 flu season, regulatory agencies including WHO and local State Departments encouraged or required continued influenza surveillance along with SARS-COV-2 testing, and the US can be expected to resume surveillance as we enter into the traditional flu season time period. Last year, for example, the New York State Department of Health required both flu and COVID testing for all patients being hospitalized for respiratory viral illness. While no similar mandates have yet been released, such co-testing would be prudent this year, as well.

So, what can we expect for the 2021-2022 influenza season?5 To date, Australia and the southern hemispheres, where flu seasons begin, has minimal or nominal number of influenza cases making season prediction difficult.6 This year in particular there are serious concerns for a severe flu season due to decreased population flu immunity from last year’s absent influenza season.

There appears to be masking and social distancing fatigue and relaxation of some of the mitigation practices. This is especially concerning as manifested by the rise of other seasonal and endemic respiratory viruses such as RSV and parainfluenza, especially as these viruses are circulating in significant amounts despite masking and social distancing of the ongoing COVID-19 pandemic. In addition to community circulation of respiratory viruses, with this year’s pattern is also different from previously observed and known seasonality. 7 Worldwide there has been a notable increase in severe acute respiratory illness (SARI) in some regions: RSV in South America; and RSV, Parainfluenza and Rhinovirus in the US.

What can we do and how can we prepare? The answer to a large part is vaccine. As in prior years, there are a number of vaccine choices available, including inactivated influenza vaccine both as egg-based and cell-culture-based products, adjuvanted vaccine, recombinant flu vaccine product, and intranasal formulation. All flu vaccines are now quadrivalent. A high-dose vaccine is available for persons ≥65, and two doses are recommended for children who had never received flu vaccine. Is it more important than ever for everyone to get vaccinated against flu. A recently published study suggests that due to non-pharmacologic interventions of the COVID pandemic, the population is more susceptible to viral illnesses, and early and widely utilized vaccination (including vaccination of children), is important in reducing susceptible population. 8

It is also possible to have flu and COVID at the same time, and although it is unclear how common that is, the possibility of “twindemic” remains a serious concern. Flu and COVID vaccines can be given at the same time, which is great news for persons who haven’t yet gotten their COVID vaccine or those receiving their third dose. As we have learned, vaccination and non-pharmacologic mitigation strategies are our best tools to prevention and protection from both flu and COVID.

References

1. Wep GIP (2021) Review of global influenza circulation, late 2019 to 2020, and the impact of the COVID-19 pandemic on influenza circulation. https://www.who.int/publications/i/item/who-wer-9625-241-264 Accessed 1 Sep 2021

2. https://www.who.int/tools/flunet

3.https://www.cdc.gov/flu/weekly/index.htm, Accessed September 1st 2021

4. August 16 Influenza Update N° 40. https://cdn.who.int/media/docs/default-source/influenza/influenza-updates/2021/2021_08_16_surveillance_updates_400.pdf?sfvrsn=9bed9dff_5&download=true Accessed 1 Sep 2021

5. https://www.cdc.gov/flu/season/faq-flu-season-2021-2022.htm, Accessed September 1st 2021

6. Rubin R (2021) Influenza’s Unprecedented Low Profile During COVID-19 Pandemic Leaves Experts Wondering What This Flu Season Has in Store. JAMA. https://doi.org/10.1001/jama.2021.14131

7. Olsen SJ, Winn AK, Budd AP, et al (2021) Changes in Influenza and Other Respiratory Virus Activity During the COVID-19 Pandemic - United States, 2020-2021. MMWR Morb Mortal Wkly Rep 70:1013–1019

8. Sanz-Muñoz I, Tamames-Gómez S, Castrodeza-Sanz J, et al (2021) Social Distancing, Lockdown and the Wide Use of Mask; A Magic Solution or a Double-Edged Sword for Respiratory Viruses Epidemiology? Vaccines (Basel) 9.: https://doi.org/10.3390/vaccines9060595