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Medisina at Politika by Dr. Rey Pagtakhan  

COVID-19 and the seasonal flu: A fearful duo

by Dr. Rey Pagtakhan

Autumn has come and the annual fall-winter influenza season – the flu – is on its way to Canada and the USA. The arrival of the seasonal flu in the midst of the COVID-19 pandemic makes for a fearful duo.

Alluding to the recent surges of COVID-19 cases across many American states and the flu season that could “pile up on top of the pandemic,” Dr. Anthony Fauci, a world leading infectious disease expert at the US National Institute of Health, recently wondered, “Are we prepared for the challenges of the fall and the winter?”

Both the Public Health Agency of Canada and the US Centers for Disease Control and Prevention have expressed similar concern. The 2020-2021 fall-winter season may probably be one of the most difficult times in North American public health experience. These concerns are all about the dual threats of two contagious respiratory illnesses in the same patient.

Canadian headlines on COVID-19

These headlines during the preceding week capture the current COVID-19 situation in Canada:

  • “As caseloads spike in four provinces, Trudeau warns that pandemic will be worse this fall” – CBC News, September 23
  • “B.C. reports 98 new COVID-19 cases, one new death” – The Canadian Press, September 25;
  • “65 new cases of COVID-19 confirmed in Manitoba, bringing active caseload to 545” – Winnipeg Free Press, September 26
  • “Ontario, Quebec stress risk of socializing amid surge in COVID-19 cases” – The Globe and Mail, September 27
  • “Ontario’s second wave of COVID-19 forecast to peak in October’” – CBC News, September 28.

The toll of the two diseases on human life

Going into the tenth month since its onset in late December 2019 in China, and the eighth month since it was officially named, COVID-19 has sickened over 33 million people and claimed the lives of at least million worldwide. It has caused severe disruption to social, financial and economic health.

According to the John Hopkins University coronavirus dashboard as of Monday, September 28, 2020, the worldwide count is 33,173,176 total cases and 998,696 deaths.

  • Canada: 155,428 total cases and 9,318 deaths.
  • The Philippines: 307,288 total cases and 5,381 deaths.
  • USA: 7,118,523 total cases and 204,790 deaths.

Reflected in these numbers are the more than half a million patients added anew to the over seven million total caseload and 200 thousand deaths in the USA. This is an average of 42,000 cases daily during the preceding two weeks. The added cases in Canada during the same period are over 17,000, an average of over 1,000 cases daily, and a total caseload of over 150 thousand. Thus, the toll on human life in North America remains huge.

Influenza’s toll on human life

Worldwide, seasonal flu is estimated to cause one billion cases, a quarter to half a million deaths, and three to five million patients with severe illness. In Canada, it is estimated to result in 12,500 hospitalizations and 3,500 deaths.

Comparison of the two diseases

The differences and similarities, some of which are superficial, between the two diseases are shown in tabulated format to better understand and appreciate the gravity of each ailment should anyone have the misfortune of contracting either or both.

Type of Disease
• Both are contagious respiratory diseases
• The pathogens use different receptors on cells to gain access to the patients’ bodies.
• The COVID-19 virus enters one way • The flu virus enters another way.
Causative Pathogen
SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2019) is the pathogen Influenza A & B viruses, of different strains, which circulate each year as the endemic pathogens
• Both viruses are transmitted by droplets, contact and fomites.
• A sick person can transmit the virus to others in droplets via coughing, sneezing, singing and talking.
• If you touch a surface with viruses on it, you can transfer the germs to yourself by touching your face.
• People with COVID or the flu may not realize they are sick and can unknowingly spread it to others.
• People with flu are most contagious in the first three to four days after their illness begins.
Incubation Period
COVID-19 median incubation period: 5-6 days Influenza median incubation period: of 3 days
Rate of Spread
• The speed of transmission is an important difference between the two viruses
• The serial interval (the time between successive cases) is different for the two viruses
• The reproductive number (the number of secondary infections generated from one infected individual) is different for the two viruses
The serial interval is 5 to 6 days. The serial interval is 3 days
The COVID-19 spreads slower than the flu. Influenza spreads faster than COVID-19.
Most healthy adults may be able to infect others beginning one day before symptoms develop and up to 5 to 7 days after becoming sick. Transmission in the first 3 to 5 days of illness, or potentially pre-symptomatic transmission, is a major driver of transmission.
The reproductive number is between 2 and 2.5 times higher than for influenza. The reproductive number is lower than for COVID-19.
Children are less affected than adults and the clinical attack rates in the 0-19 age group are low.   Children are infected by adults, not vice versa. Children are important drivers of transmission in the community.
Older age and underlying conditions increase the risk for severe infection. Those most at risk for severe infection are children, pregnant women, elderly, those with chronic medical conditions and the immunosuppressed.
• Both have a similar clinical presentation of illness from asymptomatic or mild, through to severe disease and death: fever, cough, headache, body aches, runny or stuffy nose, fatigue, and sometimes vomiting and diarrhea (especially in children); difficult breathing, pneumonia, respiratory failure.
• While the range of symptoms for the viruses is similar, the proportion of severe disease is different.
80% of infections are mild or asymptomatic, 15% are severe, requiring oxygen, 5% are critical requiring ventilation. Proportion of severe and critical infections higher than for flu infection. The proportion of severe and critical infections is higher than what is observed for flu infection.
• Sudden loss of smell or taste  
• Some children developed acute inflammatory syndrome.  
• Half of the infected have no symptoms  
Laboratory Diagnosis
• Getting tested is the best way to know for certain whether the patient has either or both of the viruses.
• A test that will check for both viruses has been developed at the CDC-USA.
Medical Intervention & Treatment
• Directed at relief of symptoms.
• Severe cases may require hospitalization and oxygen and very ill patients will need a ventilator
• Antiviral medications may shorten the duration of both
• While there are a number of therapeutics in clinical trials and more than 20 vaccines in development for COVID-19, none are licensed. In contrast, antivirals and vaccines are available for influenza.
Currently, antiviral and anti-inflammatory meds (remdesivir & dexamethasone) are only available in an intravenous form and for severe illness. They are not prescribed to patients outside of a hospital. Oral antiviral medications can address symptoms and sometimes shorten the duration of the flu. These can be prescribed for patients who are in or out of hospital.
Possible long-term damage to the lungs, heart, kidneys, brain & other organs after severe infection. Possible inflammation of the heart, brain or muscles and multi-organ failure. Secondary bacterial infections sometimes occur.
Mortality appears higher than for influenza. Mortality is usually well below 0.1%. This depends on access to quality health care.
The crude mortality ratio is 3 to 4 per cent.


Both are prevented by mask-wearing, frequent and thorough hand washing, cough etiquette, staying home when sick, avoiding crowds, and keeping the physical distance.
A vaccine is on the horizon but none are officially approved for public use. A vaccine is available and effective in preventing some of the most dangerous types or to reduce the severity or duration of the flu.

Dangers of Flu/COVID-19 dual infections

Reportedly, between two and 20 per cent of COVID-19 cases have been associated with another respiratory virus infection. Although no one knows for certain, the occurrence of COVID-19 and the flu in the same patient at the same time could, intuitively, pose the following clinical dangers: an additional challenge to differential clinical diagnosis; catastrophic injury to one’s immune system; vulnerability to develop a more severe infection with either or both diseases; a greater potential for respiratory failure and other multi-organ complications; increased risk of longer-term effects of any of those organ systems; and greater predisposition to secondary bacterial infection. Also, a greater burden on the health care system can be anticipated. The duo could precipitate a health care crisis unlike any other.

On the brighter side of medical life, the positive behavioural changes to flatten the COVID-19 pandemic curve – the preventive personal and community public health measures already learned and adopted as a habit of daily living – could conceivably lessen the impact of the seasonal flu. These would be the same personal and community public health measures we would need to guard against the dual threats. And yes, get a flu vaccination.

Effectiveness, safety & benefits of flu vaccination

The flu vaccine is effective and safe. The protection provided by a flu vaccine varies from season to season. It depends in part on the age and health status of the person getting the vaccine, and the similarity or “good match” between the viruses used in the production of the vaccine and those circulating in the community. It is not perfect, but it offers the best prevention that we have. The influenza that one may get even after vaccination would likely be less severe and recovery would be faster.

The viruses in the flu shot vaccine have been killed (inactivated), hence, the flu shot cannot cause a flu illness. The viruses in the nasal spray haven been weakened, hence, only transient minor reactions may occur and are much less than one gets from the actual flu illness.

Other known benefits from flu vaccination include a reduced risk of flu-associated hospitalization for children, working age adults, and older adults. It is also a preventive tool for people with chronic health conditions. It helps protect women during and after pregnancy and it can be lifesaving in children. It may also protect people around you, including those who are more vulnerable to serious flu illness, like babies and young children, older people, and people with certain chronic health conditions.

My wife and I get the flu shot every season for two reasons: our immune protection from the previous year’s vaccination would have declined by now; and to get the best opportunity of a “good match” between the viruses used in the production of the current vaccine and those circulating in the community. We know that by getting vaccinated and being protected against the flu, we also help others with whom we interact, indirectly.

The development of antibodies following a vaccination takes about two weeks. To ensure protection, we should get it early. Since the risk of getting the flu in Canada is higher in the: late fall, and winter. (Fall starts on September 1st and winter on December 1st), we plan to get our “flu shot” before the end of October, and well before the start of the flu season. Children who need two doses of vaccine should start the vaccination process sooner, because the two doses must be given at least four weeks apart.

The good news: well over 55 per cent of Canadians are now planning to have their flu vaccination – by flu shot or by nasal spray – in contrast to a lower percentage in prior years. Indeed, I encourage everyone, as recommended by public health authorities and medical experts, to get the flu vaccine.

It is imperative. It is our best protection against the fearful duo.

Dr. Rey D. Pagtakhan graduated from the University of the Philippines, trained at the St. Louis Children’s Hospitals of Washington University School of Medicine and the Winnipeg Children’s Hospital of the University of Manitoba (UM) Faculty of Medicine, and earned a Master of Science in Perinatal Physiology, with his thesis Initiation of Respiration, from the UM Faculty of Graduate Studies and Research. A retired lung specialist, professor of pediatrics, and Fellow of the American College of Chest Physicians, he was a former school trustee, Member of Parliament, and cabinet minister. In June 2003, he presented on “The Global Threat of Infectious Diseases” at the G-8 Science Ministers/Advisors Meeting held in Berlin.

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