Causing Seasonal Misery: The “Flu” and the “Flu-like” Virus

It’s almost the middle of winter and you start feeling sick. Runny nose, cough, sore throat, breathing problems, fever, headache, and diarrhea- all these dreaded symptoms sound familiar to you? And most certainly you attribute this seasonal misery to “common cold” or the flu.

Most people use the terms common cold and flu interchangeably, however, the flu is very different from common cold. While a “common cold” can be caused by more than 200 different viruses, the “flu” is an abbreviation for influenza. This respiratory virus is dreaded for its ability to spread rapidly through communities. When someone with the influenza coughs or sneezes, the influenza virus is expelled into the air, and anyone who inhales it can become infected. The virus can also be spread if someone touches a contaminated hard surface such as a door handle and then places their hand on their mouth or nose.

Each year millions of people suffer from flu symptoms to varying degrees of illness. For instance, children, old people, and people with weakened immune systems are more prone to the illness. Other secondary bacterial infections may follow after the flu. This season has been a particularly tough flu season. According to the U.S. Centers for Disease Control and prevention (C.D.C) reports1 (as of February 17, 2018) for flu activity during the year 2017-2018, 161,129 positive tests were performed by clinical laboratories and 35,544 positive tests performed by public health laboratories since Oct. 1, 2017. As per the FluView activity indicator2, the influenza activity is likely to remain elevated for several weeks.

However, this winter, the flu isn’t the only virus that could leave you feeling feverish and miserable, adding to the seasonal misery is another “flu-like” virus called the Adenovirus. This family of viruses, known as adenoviruses, often mimic influenza. Though very similar to the flu, there are differences between the two viruses.

Approximately 60 different types of Adenoviruses exist that can cause human infections. Most of the times, adenoviruses produce flu-like illness with fever, cough, runny nose and diarrhea and some strains of adenoviruses can also cause pink eye (conjunctivitis). Other symptoms could be more severe, for instance, inflammation of stomach and intestines, bladder infections and bronchitis (shortness of breath due to inflammation of airways). In worse cases adenovirus, has also been reported to cause neurologic symptoms such as encephalitis (an inflammation of the brain) or meningitis (inflammation of tissues surrounding the brain). Just like the flu, adenovirus can spread from person to person and can be particularly deadly in vulnerable populations like children, elderly and people with weakened immune system.

Adenovirus infections are definitely rarer than the flu. While influenza causes and estimated 12,000 to 56,000 deaths each year, the death toll for particularly bad adenovirus outbreak3 in 2007 was dramatically lower. Unlike the flu, adenovirus is not seasonal and can cause illness throughout the year. Some case of adenovirus, specifically human adenovirus type 4 (HAdV-4) have been severe or indeed fatal. According to C.D.C report published last month in Emerging Infectious Disease4, HAdV-4 might be an underestimated causative agent of acute respiratory disease. As per the report, lack of effective surveillance to determine the prevalence makes it difficult to ascertain the toll of adenovirus infection.

And while an effective adenovirus vaccine exists, it’s available only to military recruits. The adenovirus vaccine5 provides protection against two major adenovirus strains: type 4 and type 7. The above-mentioned C.D.C reports suggests licensing the vaccine for use to the civilian population. This might help us be better prepared for any future outbreaks!

However, when it comes to the ever-evolving flu, it becomes very challenging to design an effective vaccine. The flu vaccine commonly referred to as “the flu shot” may not be the most potent but is indeed the best protection you can get against the flu. There are two types of inactivated flu vaccine based on the number of influenza virus strains it contains: A trivalent (3 strains) and a quadrivalent (4 strains) vaccine. There is no preference for the use of either of these formulations. Any of these vaccines should be given as available in your area. The ideal time to take the vaccine is before the fall season starts. While the vaccine effectiveness varies based on how well it matches the circulating virus strains, recent studies show that flu vaccination reduces the risk of flu illness between 40% and 60% among overall populations.

In the beginning of 2017-2018 season, the flu vaccine for this year was thought to be barely effective. However, in a press conference last week, as reported by the New York times6, the acting director of C.D.C said that this year’s vaccine is about 25% effective against the circulating strain. In a bigger surprise the vaccine is 51% effective in children as per preliminary analysis. The C.D.C final analysis are yet to be released.

Although the flu shot might not be completely effective it does prevent thousands of deaths every year7. The bottom-line is it is always worthwhile getting your flu shot! Coming back to the flu-like adenovirus, let’s see what prevention measures the federal health agency recommends in the future. While the massive influenza outbreak this year might have led a lesser known infection like the adenoviruses silently slip away; the spread of adenovirus must not be underestimated.


1. Weekly U.S. Influenza Surveillance Report, 2017-2018 Influenza Season Week 7 ending February 17, 2018. Centers for disease control and prevention.

2. Situation Update: Summary of Weekly FluView Report. Centers for disease control and prevention.

3. Human Adenovirus Type 14. Centers for disease control and prevention.

4. Emerging infectious diseases. Volume 24, Number 2—February 2018. Centers for disease control and prevention.

5. Vaccine information Statements (VISs). Adenovirus VIS. Current Edition date: 6/11/2014. Centers for disease control and prevention.

6. The Flu Vaccine Is Working Better Than Expected, C.D.C. Finds by Donald G. McNeil Jr. February 15, 2018. The New York Times.

7. CDC Study: Flu Vaccine Saved 40,000 Lives During 9 Year Period. March 30, 2015. Centers for disease control and prevention.

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Mitali Adlakha

Is a contributor to The Almost Doctor’s Channel.


  1. Codey

    Well written article. Are there any companies venturing out into adenovirus vaccination in the near future?

  2. Vijay Adlakha

    Useful and informative article