2022 - 2023 Influenza (Flu) Season

Coexistence of Influenza and Covid-19

We are beginning to see concern from the medical and public health communities about the coexistence of Covid and Influenza during the 2022 - 2023 Flu season. There are 2 main things causing that concern.

1. 1. Larger than normal seasonal surge in Influenza. Immunity to Influenza is weak as a result of the public health measures taken to reduce the spread of Covid over the past 2.5 years. The Hong Kong public will be more susceptible, leading to more infections and a higher proportion of the infections being severe.
   2. Co-infection of Covid and Influenza. The Lancet published the findings from a study that found those co-infected with Covid and Flu were four times more likely to require breathing support and 2.4 times more likely to die^[1].

Vaccination against both diseases has never been more important, and they can now both be done at the same time.

Why might the flu season be bad this year?

The 2020 -2021 and 2021 - 2022 flu seasons were both light. Figures 1 and 2 compare Influenza Like Illness (ILI) consultation rates from 2018 to the beginning of the 2022/2023 season. Data in Figure 1 is from Private Medical Practices (PMP) in Hong Kong whereas figure 2 is from General Outpatient Clinics (GOPC) but reflects a shorter period^[2].

Figure 1: Rates of Influenza-Like Diagnosis in Private Medical Practitioners Clinic (PMP)^[2]

Figure 2: Rates of Influenza-Like Diagnosis in General Out-Patient Clinics (GOPC)

It shows Influenza rates prior to the Covid pandemic were much higher. The difference comes down to Covid-related changes in behaviour. Hong Kong has maintained aggressive restrictions to prevent the spread of Covid for nearly 3 years. The wearing of masks, practising regular hand hygiene and social distancing was effective at curbing the spread but had numerous unforeseen consequences. The impact on mental health has been widely documented, but the impact (good or bad) on other communicable diseases like Influenza is less well recorded as restrictions have only begun to ease in recent months.

Given Influenza spreads in a similar way to Covid, the restrictions Hong Kongers have been bound by also protected them against Influenza. This is a good thing in the short term but less so in the longer term. As we see restrictions decrease, we will be more vulnerable to Influenza as we have not been able to gain any natural immunity through community infection.

There is a significant risk that Hong Kong will suffer from a surge in Influenza cases which combined with Covid will be an enormous challenge for the health system, particularly when we start to see co-infection. Many are predicting that we will feel the effects this coming flu season. At an individual level, the best solution is to get the Influenza vaccine at the beginning of the season, i.e. September/October.

How shall I prepare for the flu season?

Like Covid, the flu can be a serious illness, particularly in the vulnerable. Influenza viruses and the Coronavirus spread in similar ways, so measures to avoid Covid infection are likely to lessen your chances of catching flu too.

Here’s what you can do to be prepared for the 2022 - 2023 flu season:

1. 1. Get your flu shot. It is clinically proven that getting the flu vaccine reduces your risk of getting ill and if you do get ill, it reduces the chances of severe illness. It not only protects you but protects your friends and family, particularly those who are at the highest risk. The CDC recommends that everyone over the age of 6 months gets vaccinated^[3]. The optimum time to get the flu vaccine is in September and October so that you are prepared for the worst parts of the flu season between November and March. Given that the Hong Kong population will be more susceptible this year, we are expecting to see the flu season show up sooner and last for longer. OT&P recommends the earlier in the season you get the vaccine, the better.
   2. What to do if you get sick. The flu and Covid have many overlapping symptoms, such as fever, cough, shortness of breath and muscle aches. If you develop these symptoms, you can rule out one or the other by taking a Covid rapid antigen test (RAT) which is now widely available at affordable prices. Secondly, you may choose to make an appointment with your doctor. They will inform you of what to do next and may prescribe Covid-specific antiviral treatment or antiviral treatment for the flu.

Winter is also the season for other contagious viral illnesses such as Respiratory Syncytial Virus or RSV (common for children) and Norovirus (a stomach bug). To ensure that your immunity to common communicable diseases is in the best possible shape, you can review your vaccine status with your doctor. More information on the vaccines you should have can be found on our vaccine page.

Many of the recommendations listed above and others that are used for curbing the spread of Covid will help keep these viruses at bay. Washing your hands regularly, disinfecting surfaces often and staying home when you’re sick are all good practices during the winter. 

References

1. Swets, M. C., Russell, C. D., Harrison, E. M., Docherty, A. B., Lone, N., Girvan, M., Hardwick, H. E., Visser, L. G., Openshaw, P. J. M., Groeneveld, G. H., Semple, M. G., & Baillie, J. K. (2022, March 25). SARS-COV-2 co-infection with influenza viruses, respiratory syncytial virus, or adenoviruses. The Lancet. Retrieved September 28, 2022, from https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(22)00383-X/fulltext

2. Flu Express - chp.gov.hk. Flu Express. (2022, September 22). Retrieved September 28, 2022, from https://www.chp.gov.hk/files/pdf/fluexpress_week38_22_9_2022_eng.pdf

3. Centers for Disease Control and Prevention. (2019, August 2). Flu shots for children. Centers for Disease Control and Prevention. Retrieved September 28, 2022, from https://www.cdc.gov/vaccines/parents/diseases/flu.html#:~:text=For%20the%202020%2D2021%20flu,through%2049%20years%20of%20age