Flu, The Smart Virus

The HWN Team | Insider
Flu, The Smart Virus

image by: Mike Mozart

Flu vaccinations have become an annual event in most developed countries, yet the flu continues to affect tens of millions of people each year and causes 250,000 to 500,000 deaths worldwide. So, what's wrong? Is the flu virus smarter than us?

It's flu season somewhere and we are not talking about a pandemic. Flu usually starts in the fall and subsides in late spring and because of its seasonality, it differs between the Northern and the Southern hemisphere. The United States Centers for Disease Prevention and Control (CDC) gives the following statistics on flu:1

  • 5 to 20% of the population gets the flu annually
  • Yearly, 200,000 cases are hospitalized due to severe flu complications
  • Yearly, up to 49,000 cases can be fatal

Flu, otherwise known as influenza is a respiratory illness caused by viruses. There are many different types of flu, from the swine flu to the most feared avian flu. There are three types of influenza viruses: Type A, Type B and Type C. Each type consists of different subtypes and substrains. Influenza types A and B are responsible for most of the flu epidemics.2

The CDC gives a more in-depth description of the viruses:

  • Influenza A viruses are of subtypes based on two proteins on the surface of the virus: the hemagglutinin (H) and the neuraminidase (N). 16 different hemagglutinin subtypes and 9 different neuraminidase subtypes currently exist. The current subtypes of influenza A viruses in humans are A (H1N1) and A (H3N2).
  • Influenza B viruses do not have subtypes but can be further broken down into different strains.
  • Influenza C seems to be relatively benign compared to the first two, can cause mild respiratory illness which is not as contagious as the others and thus hasn’t been linked to any of the flu epidemics.

Influenza symptoms may be mild to severe to life-threatening. The following symptoms, also commonly called “flu-like symptoms” are associated with the flu:

  • High fever
  • Headache
  • Chills and shivering
  • Sore muscles
  • Fatigue
  • Dry cough
  • Red, watery eyes
  • Sore throat
  • Runny or stuffy nose
  • The so-called “tummy flu” symptoms may also occur in children, which include abdominal pain, vomiting, and diarrhea.

Flu symptoms shouldn’t be confused with the ordinary cold. A cold usually doesn’t cause high fever, muscle pains or stomach symptoms. The incubation period of the flu can vary from a few days to a week. This means it takes a few days before the symptoms appear. During this “asymptomatic period”, the infected person is already a carrier of the disease and is therefore highly contagious.

The flu can last from a few days to less than two weeks. However, in certain cases, complications can develop which are potentially life-threatening. Some of these complications are bronchitis, pneumonia, sinusitis, and ear infections.

Anybody can get the flu but those who are highly susceptible to the flu are young children, the elderly and those with existing health conditions and weakened immune systems. The following chronic health problems are worsened by the flu:

  • Asthma and wheezing
  • Chronic lung problems such as lung cancer and cystic fibrosis
  • Congestive heart failure

What makes the flu virus so smart?

Flu is hard to diagnose

Flu-like symptoms are associated with many other diseases aside from the seasonal flu making it difficult early on for doctors to diagnose the illness just based on the overt symptoms. There are many laboratory tests which can confirm whether a person has the flu or not but these tests cost money and time and are therefore impractical.

But, in times of outbreaks and epidemics, it is important to perform tests to confirm that it is really the flu. Usually, flu cases are diagnosed based on tests performed in a few individuals within a group. If one or two persons test positive for the flu in a closed environment such as a family, a day care, a boarding school, a small clinic, an army barrack, or a crew ship, then the likelihood of subsequent illnesses within the group as being flu is rather high.

Samples for flu testing are usually secretions from the nose and the throat, collected either by sterile swab, nasal wash, or aspiration. Samples are collected within the first 4 days of the onset of symptoms, There are rapid influenza tests which can give results in 30 minutes. The tests are 70% sensitive in detecting the flu and are prone to false negatives. Another alternative is the more reliable but time consuming viral culture which takes about 3 to 10 days. In times of suspected outbreaks, both rapid tests and viral cultures are performed. The CDC web site gives a run down of the many different tests available for flu detection.3

Flu is a very contagious infection

Influenza viruses attack the epithelial cells lining the respiratory tract starting from the nose, throat, and down to the lungs. They do this by binding using hemagglutinin and/or new hemagglutinin and neuraminidase proteins on the surface of the cells. Transmission occurs from person to person via the droplets that are released in the air when a person with flu coughs or sneezes. Transmission can be thru direct transmission which happens when droplets from an infected person are transferred directly from one person to another or indirect transmission happens when droplets from an infected person are transferred to inanimate objects, which are then touched by another person.

Influenza viruses can change with time, like many viruses, thus producing new strains each season

This happens one of two ways:

  • Antigenic drift happens through small but constant changes in the viral structure. This process is slow and can lead to new strains after several seasons. This is the typical change observed in influenza type B viruses but can also occur in type A viruses.
  • Antigenic shift happens abruptly and creates a major change that can lead to a new subtype. This change results in a major change in the protein structure. This type of change has been observed to occur in influenza type A viruses only.

Prevention is still the best defense against the flu.4

  • The CDC recommends the following simple measures one can take in our daily routine:
  • Cover your nose and mouth with a tissue when you cough or sneeze. Throw the tissue in the trash after you use it.
  • Wash your hands often with soap and water, especially after you cough or sneeze. Alcohol-based hand cleaners are also effective.
  • Try to avoid close contact with sick people.
  • If you get the flu, …stay home from work or school and limit contact with others to keep from infecting them.
  • Avoid touching your eyes, nose or mouth.

However, despite the ongoing controversy that surrounds vaccinations in general most people still believe the ultimate preventive measure is annual vaccination.5 But, the flu vaccine itself remains controversial, even more so now since the 2010 Swine flu pandemic. Why?

Vaccine side effects

Like all pharmacological agents, flu shots can have some side effects. Most of these side effects are mild and resemble mild flu-like symptoms. Rare severe side effects, mainly in the form of allergic reactions to the vaccine or one of its components have been reported. The health authorities are requesting that all side effects be reported. In case of serious vaccine reactions, the National Vaccine Injury Compensation Program helps to pay for the care of the patient.6

Some inactivated flu vaccines have contained thimerosal in the past, a form of mercury used as preservatives for vaccines. In recent years, there have been concerns about the link between thimerosal and autism in children. Although the original reference was discredited in 2010 this controversy continues although there is still no ample scientific evidence to prove this link.7

Vaccine effectiveness

Due to the constantly changing nature of the influenza viruses, flu vaccines do not afford 100% and lifetime immunity against the flu. Perhaps the main shortcoming of the flu shot is its efficacy, which is highly dependent on how well the vaccine is matched to the circulating influenza viruses of that season. Although scientists try to predict the current causative strains from the previous year, matching is not 100%. For this reason, the efficacy of the vaccine in protecting healthy adults from the flu is only 70 to 90% and even less in children and the elderly.8

Some studies on efficacy give even more disappointing figures. Researchers at Strong Memorial Hospital, Rochester, NY looked at the efficacy of flu shots given during the flu seasons of 2003 to 2004 and 2004 to 2005 in several counties. The study results indicate that flu shots did not prevent the flu and flu-related illnesses in children aged 6 to 59 months. According to the researchers, the vaccines during these two seasons were not optimally matched to the flu strains causing the illness. Upon further investigation the vaccine effectiveness in 2003-2004 was 44% and 2004-2005 was 57%.9,10

If you decide to take the flu shot, here's some things you need to know.

Flu shots are usually given prior to the next flu season and afford protection for about a year. However, it takes about two weeks before the protection kicks in. People are asked to talk to their doctors about the getting the flu shot. In addition, the versatile HealthMap can help you locate the nearest flu clinic in your area.11

Flu vaccines contain different strains of the influenza types A and B but not type C and each season flu vaccines are updated by adding strains collected and identified from the previous season. Always check the CDC website for the latest combination.12

Based on the 2006 guidelines of the Federal Advisory Committee on Immunization Practices (ACIP), annual flu shots are recommended for children aged 6 months to 5 years old. ACIP expanded the guidelines to include adolescents up to 18 years old.  Vaccination is also highly recommended for people in key professions which may expose them to the infection and spread it to others. These include health care professionals (nurses, doctors), care givers (for children and the elderly), and those working and living in closed units such as dormitories, barracks, or correctional facilities. 13,14

The CDC gives the following information on the most commonly used flu vaccines:

The inactivated vaccine or the flu shot is made from different strains of killed flu viruses. This vaccine is recommended for children from 6 months to 18 years old as well as those older than 50 years old. In addition, people who are not qualified to receive LAIV are recommended to have this vaccine.

The intranasal vaccine is the live, attenuated influenza vaccine (LAIV) made from living but weakened flu viruses of several types and strains. LAIV is prescribed for people aged 2 to 49 years old. LAIV should not be given to pregnant women, children under 2 years old and adults above 40 years old, and those with the following conditions:

  • asthma or wheezing episodes (children)
  • heart, lung, kidney or liver disease
  • metabolic disorders such as diabetes, and blood disorders such as anemia.
  • compromised immune system (e.g. HIV)
  • muscle or nerve disorders
  • long-term aspirin treatment (children)

If you are still unlucky and get the flu how do you treat it other than symptomatic care?

Currently there are two antiviral pharmacological agents (neuroaminidase inhibitors) available, but they must be started early in the illness to be of any value:

  • Oseltamivir / Tamiflu is approved for treatment of persons aged 1 year and older and is licensed for use as chemoprophylaxis in persons aged 1 year and older.15
  • Zanamivir / Relenza is approved for treatment of persons aged 7 years and older and is licensed for use as chemoprophylaxis in persons aged 5 years and older.16

However, flu can become resistant to pharmacological agents because of the seasonal changes in the types and strains of influenza viruses and because of the ability of flu viruses to change. In fact WHO in 2009 discouraged the use of previously used anti-flu drugs such as Amantadine and Rimantadine because the current circulating strains of flu viruses were resistant.

Alright, who is watching out for those flu pandemics?

The United Nations, through the World Health Organization (WHO) is on the frontline in the global surveillance of the flu. The Global Influenza Surveillance Network (GISN) was set up as early as 1952. It ensures rapid reporting and updates on flu activity worldwide. This global system of surveillance includes more than 110 laboratories in 83 countries. The WHO GISN issues regular updates of seasonal influenza activity in the world. It also helps in the detection of new strains of the flu viruses which are isolated and stored for possible inclusion in the next generation of vaccines. It has recently set up FluNet, a web-based tool for surveillance, reporting, and alert mechanisms.17,18

The European Influenza Surveillance Scheme (EISS) includes 26 European Union member countries as well as non-members Norway, Serbia, Switzerland and Ukraine. EISS issues a weekly report on influenza activity in 30 countries in Europe. It collects data from more than 25,000 sentinel doctors covering a total population of 498 million people in Europe.19

In the U.S., the CDC is responsible for the national influenza surveillance. It is dependent on reports of more than 1500 sentinel doctors all over the U.S. and its territories. The CDC, too, issues a weekly surveillance bulletin. In 2005, President George W. Bush launched National strategy for pandemic influenza in response to the avian flu problems in Asia.20,21

The latest service Google Flu Trends claims that it can estimate flu activity up “to two weeks faster than traditional flu surveillance systems.” Unlike data from the WHO, EISS, CDC and other surveillance groups which are based on reports by sentinel health care professionals, Google Flu Trends bases its predictions on the number of people searching for flu-related topics using the Google search engine.22

Google’s data actually compared well with that of the CDC’s thereby indicating a close relationship between influenza-like illnesses (ILI) and “flu search engine query data” on the Internet. Data reported to the CDC takes up to two weeks to process. However, query data can actually be analysed on the daily basis, thus making flu activity estimates available faster, on a daily basis. In addition to regular updates, Google Flu Trends also presents the data in graphs, maps, and animations which are easy to comprehend by the general public. 

Google is now working together with the CDC in flu surveillance and their work has been published in the prestigious scientific journal Nature. The article concludes: “Harnessing the collective intelligence of millions of users, Google web search logs can provide one of the most timely, broad-reaching influenza monitoring systems available today. Whereas traditional systems require 1–2 weeks to gather and process surveillance data, our estimates are current each day".23

The Bottom Line

Even if you get the flu vaccine and take everyday preventive action you can still be unlucky and get the flu...it's one of the smartest viruses known to man!

Published January 1, 2009, updated August 19, 2012


  1. Seasonal Influenza, CDC
  2. Types of influenza viruses, Seasonal Flu, CDC
  3. Laboratory diagnostic procedures, Seasonal Flu, CDC
  4. Take 3 Steps To Fight The Flu, Seasonal Flu, CDC
  5. Faces of Influenza, American Lung Association
  6. National Vaccine Injury Compensation Program, Health Resources and Services Administration, U.S. Department of Health and Human Services
  7. Novella S, The Lancet retracts Andrew Wakefield’s article, Science - Based Medicine, February 3, 2010
  8. Seasonal Influenza Vaccine Effectiveness, CDC
  9. Szilagyi et al, Influenza vaccine effectiveness among children 6 to 59 months of age during 2 influenza seasons: a case-cohort study, Arch Pediatr Adolesc Med. 2008 Oct;162(10):943-51
  10. Eisenberg et al, Vaccine effectiveness against laboratory-confirmed influenza in children 6 to 59 months of age during the 2003-2004 and 2004-2005 influenza seasons, Pediatrics. 2008 Nov;122(5):911-9
  11. Flu vaccine locator, HealthMap
  12. Flu season, CDC
  13. Prevention and Control of Influenza, Recommendations of the Advisory Committee on Immunization Practices (ACIP), MMWR, July 28, 2006
  14. Key Facts About Seasonal Flu Vaccine, CDC, July 6, 2012
  15. Oseltamivir, PubMed Health, January 15, 2012
  16. Zanamivir Inhalation, PubMed Health July 1, 2010
  17. WHO Global Influenza Surveillance and Response System (GISRS), WHO Collaborating Centres for Reference and Research on Influenza
  18. FluNet, WHO
  19. European Influenza Surveillance Network(EISN), European Centre for Disease Prevention and Control (ECDC)
  20. FluView, Seasonal Flu, CDC
  21. National Strategy For Pandemic Influenza, Homeland Security Council, The White House, November 2005
  22. Ginsberg et al, Detecting influenza epidemics using search engine query data, Nature 457, 1012-1014 (19 February 2009)
  23. Flu Trends, Google.org

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