Will There Be a Twindemic?

Will we face a Twindemic this winter?

Twindemic” is a term that has not yet been in the headlines but is likely to become part of our lexicon as the summer progresses. Twindemic refers to the possibility that we will see continuing cases of COVID-19 together with severe influenza forcing the country to deal with two serious diseases at the same time.

Influenza has been with humans for centuries, and certainly since the 1918/1919 “Spanish flu” pandemic we have respect for a disease that  caused 50-100 million deaths worldwide just 100 years ago. There were additional influenza pandemics in 1957, 1968, and in 2009, with estimated numbers of worldwide deaths of 1.1 million, 1 million, and 284,000, respectively. In addition to pandemics, seasonal influenza has taken its toll as well. In the U.S., the 2018-2019 influenza season counted 35 million cases, 490,000 hospitalizations, and 34,000 deaths.

With the onset of the COVID-19 outbreak (declared a pandemic by the WHO in March 2020), we have all experienced an unforeseen and unpredicted catastrophe resulting in almost 4 million deaths worldwide with more likely. Hopefully the availability of a sufficient number of vaccine doses and the timely distribution globally will bring the pandemic under control. Unfortunately, the emergence of SARS-CoV-2 variants may complicate our efforts to achieve this goal. Time will tell if additional variant strains will emerge which make our present vaccines unable to efficiently protect against COVD-19 infection. In addition, we still do not know whether SARS-CoV-2 will change over time leading to a situation  similar to that observed with influenza viruses,  which has created the need  for an annual revaccination with a formulation of strains matching the actual variants circulating in the population. In any case, we have entered an unprecedented period of two pandemic pathogens — influenza viruses and SARS-CoV-2 –, threatening our fabric of life all over the planet.

Several important and troubling questions arise as to the possible impact  of these two simultaneous infections:

1) Did influenza cases abruptly decline last winter  as people stayed isolated and wore masks because of widespread COVID-19 outbreaks?

The effects of social distancing and of wearing masks on the transmission of influenza viruses had previously never been seriously studied. Thus, it was/is not known what impact a nationwide social distancing and mask wearing campaign brought on by the COVID-19 outbreak would do to the human-to-human transmission of other respiratory illnesses. However, the simple explanation of maintaining appropriate distances between people and cutting down on aerosol transmission by nose and mouth protection appears to be accepted by many  to be responsible for dramatically lower influenza rates (increased hand washing also may have played a part). In fact, the incidence of influenza including the death rate (winter 2020/2021) was one hundred times lower than in most other years in the U.S.

2) Should we anticipate that influenza will return this  fall/winter?

If social distancing and mask wearing  led to drastically lower influenza cases since last winter, we should be prepared for an increase in influenza virus infections for the 2021/2022 winter because of the lifting of the COVID-19 restrictions. We already see this year an increase in respiratory syncytial virus, regular coronavirus, and rhinovirus infections which may all be related to the relaxation of anti-COVID-19 measures. This scenario may forewarn of a more serious winter season in terms of the increased number of influenza infections and of other seasonal pathogens than what was observed during the 2020-2021 season.

3) Do masks protect against influenza virus infections?

The wearing of masks also prompts social distancing so that it may be difficult to separate the benefits of keeping greater distances as compared to preventing aerosol transmission through face covering. We will have to intensify studies addressing this question and to find solutions to better protect us against respiratory agents in general. Such non-medicinal approaches may be important future strategies to curb respiratory diseases including influenza.

We must recognize how fortunate we are.  Even the simultaneous presence of two pandemic agents – the so-called “twindemic” — does not represent the threat it could be because we have effective precautions against both, as well as  potent antiviral drugs to treat influenza viruses.

Over the past 18 months we’ve come a long way in understanding viruses and in implementing a remarkable response. But we are not yet finished with the pandemic, or perhaps better put the pandemic is not yet finished with us. But I am confident, like many other great health challenges we have faced previously, we will overcome this!

Source: Dr. Peter Palese, Ph.D.

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