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What is a twindemic and why should everyone be very concerned?

Americans have been fortunate on one major public health issue since the COVID pandemic started. Influenza or “flu” rates have been at historic lows in the US during the last 3 years. Unfortunately, this year shapes up to be very different.

The flu season in the U.S. stretches generally from September to March and parallels the Northern Hemisphere's fall and winter. Several theories abound about why this seasonality occurs. The advent of the season in the fall follows the resumption of schools and business after the summer holidays and travel. In the last two seasons, influenza cases have been far below pre-pandemic levels as normal social interactions have been absent. Public health officials have not had to worry about a “twindemic” or a combination of flu and COVID cases occurring simultaneously at heavy volumes.

The experience in Australia tells us this year will be different and that is concerning on multiple levels. Australia and other Southern Hemisphere countries have had an early and severe flu season. These countries serve as a barometer of the U.S. flu season to public health officials for their strains and their volume. Already predictions are swift that the flu season will be the worst in years in the U.S. as Australia has had its worst season in 5 years.

However, other factors are going to magnify the severity of the flu season and truly threaten to create a true twindemic.

Pandemic fatigue will be the biggest instigator of a severe flu caseload. Due to widespread masking, distancing, remote work, and zoom learning, the last two flu seasons have been relatively nonexistent. These last two mild flu seasons have given people less overt reasons to receive their seasonal flu vaccines. Without recent flu reminders, people may not go and obtain their shots this year. Hesitancy and resistance to vaccines in general as a result of COVID misinformation will also decrease the numbers of people who receive flu vaccines. With almost all schools in sessions and now essentially maskless, the timing is ripe for an early and sustained flu season. Nursing homes and other health centers may become areas of spread as the CDC just revoked vaccine mandates at these institutions.

Immunological factors will additionally magnify the severity of the flu season. The absence of flu exposure for several years will make many individuals vulnerable to flu as they may not have any residual immunity from previous flu seasons. This scenario is especially frightening for small children who may be especially vulnerable to any flu challenges this season. Children under 5 may never have had flu exposure and now that they may be socializing for the first time, they are subject to very severe flu-related illnesses.

Higher influenza rates this year will also create other societal problems. The superimposition of flu cases on the still existing pandemic will lead to diagnostic confusion. People will not know whether they will have the flu or COVID and may not undergo appropriate treatment. The diagnostic dilemmas will magnify the morbidity and spread. These individuals will also not understand if they should quarantine or for how long. They may assume they are not exposing someone to their flu or COVID by thinking that the individual already had a recent case of that illness, but they may be attributing this logic to the wrong disease.

Businesses and schools will have major problems during a twindemic. More concurrent illnesses will lead to staffing shortages. The standard predictability of allotted sick days to each employee may become highly erroneous and create production challenges. Substitute teachers could be in demand. Supply chain disruptions could again receive headlines. Hospital beds may become scarce with increased flu and COVID cases both needing major inpatient resources.

However, many of these problems can be mitigated by action now.

The most important step is to prevent as many cases as possible of both diseases. Flu vaccines have to be taken immediately for all eligible persons to receive the maximum duration of protection. Prestigious universities such as Harvard and Berkeley have already realized this and mandated flu vaccines for their faculty and students. Boosters for COVID need to be encouraged now for everyone with eligibility whose last shot was over 6 months ago.

Testing for both these diseases will be crucial for the proper diagnosis. One cannot assume if they are sick they have COVID or the flu. They will need to test for both aggressively or risk an erroneous diagnosis that could completely yield the wrong treatment and produce major workforce disruptions. In a busy flu season, businesses cannot have everyone take a 5 or 10-day quarantine for the flu but this might be appropriate for COVID. They also should not be diagnosing anyone with either disease without ensuring the safety of their contacts. Correct diagnoses will help determine staffing capabilities and quarantine durations while maximizing the chances of superior productivity. Having a handle on the proper diagnosis can also protect other co-workers and students as well as their families and loved ones.

The threat of twindemic is officially real. Attention to this risk along with appropriate preparation and education will allow institutions and individuals to navigate the next phase of the pandemic with the optimal chances of professional and personal success.

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