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Vol 20, No. 09, September 2016   |   Issue PDF view/purchase
Do Your Part to Stop Infectious Disease from Spreading
Insights from Infectious Diseases Expert — Dr. Leong Hoe Nam

Dr Leong Hoe Nam is an Infectious Diseases Specialist. He graduated from NUS in 1996, and obtained his MRCP and M Med in 2001. Thereafter, he began his advanced specialist training in infectious diseases. Dr Leong further pursued his interest in virology at the Royal Free and University College Medical School, London under a fellowship awarded by the National Medical Research Council. In 2008 he was awarded a second research fellowship to train at the University of Columbia, New York, on emerging pathogens. Dr Leong has been directly involved in the care of transplant patients, individuals with multi-drug resistant organisms, tuberculosis, HIV, surgical complications, viral infections and complex medical problems. He had first-hand experience in managing outbreak situations including SARS and H1N1 pandemic infection. He has also published several research papers on virology. Dr Leong was a clinical tutor at the Yong Loo Lin School of Medicine. He was a faculty member at the Duke-NUS Graduate Medical School and still maintains his adjunct position as assistant professor while working at Mt Elizabeth Novena Specialist Centre.

1. How many types of influenza (flu) viruses exist, and which is/are the common ones?

Influenza viruses are divided into three types: influenza virus A, influenza virus B and influenza virus C, based on antigenic differences in their structural proteins. Influenza C viruses cause very mild infections whereas influenza A and B viruses are responsible for seasonal flu.

Influenza A viruses are further classified into subtypes according to the properties of their major antigens: the hemagglutinin (H) and the neuraminidase (N). Type B influenza viruses are not divided into subtypes based on antigens. However since the mid-1980s, B viruses can be categorized into two families called lineages: B/Victoria and B/Yamagata.

While it is true that type A viruses contain many combinations of H and N strains, most of these subtypes only circulate in birds. The type A viruses that currently circulate in the human population are H1N1 and H3N2. The two B viruses that currently circulate in the human population are the Victoria and Yamagata virus. As such, there are four main strains of influenza virus that currently affect humans [1]. These are two strains of Influenza A (H1N1 and H3N2) and two strains of Influenza B (Victoria and Yamagata).

Both influenza type A and B viruses are more common in Singapore. However for the first quarter of this year, we saw large proportions of influenza B. It is interesting to note that more than 70% of polyclinic attendance due to cough in the first quarter of the year was caused by influenza. About two thirds of these cases were caused by influenza B.

2. Do influenza viruses mutate to other form or shift from one strain to another?

Yes, influenza viruses constantly mutate and change. One of the ways they change is by the “antigenic drift”, the process where small genetic changes happen slowly over time to produce viruses that are quite closely related to one another.

The other type of change that takes place is called an “antigenic shift.” This refers to an abrupt, major change in the influenza A viruses, resulting in new protein antigens in influenza viruses that infect humans. These shifts result in a new influenza subtype or a virus emerging that is different from the existing subtype in humans. For example, one such “shift” occurred in 2009, when H1N1 virus with a new combination of genes emerged to infect people and caused a pandemic due to its quick spread.

The change in circulating seasonal flu viruses calls for constant evaluation by experts. This also means that there is a need to get vaccinated against influenza each year. This is especially true for those at higher risk of developing influenza-related complications, such as children below five years old, elderly people above 65 years of age, pregnant women and people with pre-existing chronic health conditions (asthma, chronic obstructive pulmonary disease (COPD), diabetes, heart disease) as well as healthcare practitioners.[2]

The influenza vaccine, in general, offers a one-year protection for most people. As the composition of the virus changes frequently, individuals should be given an updated vaccine with every change.

In addition to the groups above, individuals who come in contact with those at risk of influenza infection should be vaccinated. These include family members, healthcare workers, and caregivers of these individuals.

3. What are some misconceptions between influenza and common cold?

Misconception Fact
Influenza is the same as the common cold
  • Influenza (flu for short) is an acute viral infection caused by a number of “flu” viruses.
  • It is often confused with the common cold (i.e. runny nose, scratchy throat, non-stop sneezing) but both are caused by different viruses and have different symptoms. Influenza has more constitutional symptoms, like fever, headache and muscle aches. Colds tend to cause more upper respiratory tract symptoms.
  • Influenza can result in more severe symptoms, and at times can lead to death, especially in high-risk groups (i.e. elderly people above 65 years of age, pregnant women and people with pre-existing chronic health conaditions)
Vaccination is only required when travelling to temperate countries
  • Flu is present all-year round in a tropical country like Singapore, with two peaks in April – August and November – February. The greater peak is in April – August.
  • This creates the need for Singaporeans to be protected throughout the year
accination is only for children
  • While children below five years old and elderly above 65 years old are at higher risk, adults need vaccination too as influenza spreads easily from person to person, affecting people in any age group.
  • Flu infections could also lead to increased vulnerability to other infections (e.g. pneumonia)

4. Could the influenza virus mute our respiratory system? What could the influenza virus do to our immune system?

Influenza has the ability to decrease our immune response, which causes immunosuppression. This puts our bodies at risk of secondary infections, such as bacterial infections.

The symptoms caused by influenza include fever, muscle pain, and cough [2]. Acute symptoms and fever may persist for up to 7-10 days, while weakness and fatigue may be present for weeks [3].

Influenza illness usually starts suddenly and may include the following symptoms [4]:

  1. Fever (usual range 38°- 40°C , lasting 3-5 days)
  2. Chills
  3. Headache
  4. Fatigue (may be extreme)
  5. Muscle pain
  6. Cough (usually non-productive)
  7. Runny or stuffy nose
  8. Sore throat

However, influenza can cause more severe infections, such as pneumonia, which can result in hospitalisation or even death. Children may get sinus problems and ear infections. Other complications can include dehydration, and worsening of chronic medical conditions, such as heart failure, asthma, or diabetes.

When the body responds to an influenza infection, it upregulates and produces interferon, which in turn mutes the body’s response to a bacterial infection. In other words, it predisposes the body to a bacterial infection. We often see bacterial infections (Staphylococcus aureus or Streptococcus pneumoniae) causing secondary infection after an influenza event because of this tag-team effect.

5. Is it true to say people living in tropical region like in Southeast Asian countries, are less prone to get infected by the influenza viruses than those in temperate countries?

No, that is a misconception. Studies have shown that tropical countries like Singapore demonstrate comparable influenza-related morbidity and mortality rates to temperate countries like the USA. [5] The two influenza A viruses and two influenza B viruses have been co-circulating in Singapore most of the time, with influenza B representing approximately up to 70% in the first quarter of 2016. [6] Influenza viruses are widely prevalent in Singapore all year round with two peaks in April-August and November-February.

6. Please briefly share about the burden of influenza in Singapore and worldwide, and what can we do to reduce the burden.

Every year, there are 3-5 million severe flu cases, with 250,000-500,000 deaths globally [7]. In Singapore, all 4 strains of influenza are circulating – with type B viruses causing epidemics every 2-4 years, resulting in a significant disease burden [8]. Currently, the proportion of type A and B influenza virus circulating in Singapore is 43% and 57% respectively [9]. Usually, adults above 65 years old, and those who have existing chronic diseases (diabetes, cardiovascular, lung diseases etc.) die from the disease. The younger the child, the greater the risk of hospitalisation with each influenza infection. Approximately 1 in 10,000 children may develop the uncommon complication of encephalitis after influenza infections.

People should get vaccinated to protect themselves against influenza, reducing the burden of illness, doctor’s visits and missed time from work or school. Apart from that, people can also adhere to preventive measures to avoid the risk of transmission such as:

  • Avoid close contact with people who are sick
  • Stay home when you are sick
  • Cover your mouth and nose
  • Wash your hands and keep them clean
  • Avoid touching your eyes, nose or mouth
  • Get adequate amount of sleep, be physically active, manage your stress, drink plenty of fluids and eat well

Some studies have shown a benefit in wearing masks and using alcohol hand rubs in families with active influenza infection. Wearing masks prevent droplet transmission, the mainstay of transmission. Using alcohol hand rubs reduces the risk of transmission via contact. However, the efficacy of this protection method may not be consistent primarily because of the slow execution of the intervention (wearing masks and washing hands) compared to the rapid transmission of the virus.

FluQuadriTM is a quadrivalent influenza virus (QIV) vaccine launched by Sanofi Pasteur, indicated for the prevention of influenza disease caused by two influenza A subtype viruses and two type B viruses contained in the vaccine It induces antibody responses against the 4 following strains, including an additional B strain not covered in existing trivalent vaccines. It is the only 4-strain influenza vaccine approved for use in patients from six months of age and older. The vaccine was first made available in the United States during the 2013 influenza season.

7. Would the new influenza vaccine FluQuadriTM from Sanofi Pasteur offer better protection?

Yes, the quadrivalent flu vaccine is designed to protect against four different flu viruses; two influenza A viruses and two influenza B viruses. For the previous years, flu vaccines protected against only three different flu viruses (trivalent). This included an influenza A H1N1 virus, an influenza A H3N2 virus and one B virus. This means that the vaccine only offered protection against one B virus, even though there are two very different lineages of B viruses that both circulate during most seasons. As such, adding another B virus to the vaccine aims to give broader protection against circulating flu viruses. Furthermore, it is the only 4-strain influenza vaccine approved for use in children as young as six months of age and older adults.

Many individuals have commented that they still develop influenza despite being vaccinated with the influenza vaccine. This can be explained by the lack of full protection (3 out of the 4 circulating strains) in previous vaccines. Sanofi Pasteur now offers complete coverage for people as young as six months old. This fuller protection is unmatched by any other vaccine product.

8. What do people need to take note of to prevent Influenza?

People should get vaccinated to protect themselves against influenza. Vaccines have been used for more than 60 years and are the most effective way to prevent flu infection and related severe outcomes. The WHO and the Ministry of Health in Singapore recommend annual vaccination for the below groups due to the decrease in our immunity each year [3]:

  • Children aged six months to five years
  • Elderly individuals (≥65 years of age)
  • Individuals with chronic medical conditions (heart, lung, kidney, liver, blood or metabolic diseases)
  • Pregnant women at any stage of pregnancy
  • Care givers of those at high risk and healthcare workers
  • People in intermediate/ long term care facilities

People can also adhere to safety measures such as:

  • Avoiding close contact with people who are sick
  • Staying home when you are sick
  • Covering your mouth and nose.
  • Washing your hands and keep them clean
  • Avoid touching your eyes, nose or mouth.
  • Getting an adequate amount of sleep, be physically active, manage your stress, drink plenty of fluids and eat well.


  1. WHO Collaborating Centre for Reference and Research on Influenza, https://www.influenzacentre.org/aboutinfluenza.htm
  2. CDC Hajj and Umrah in Saudi Arabia. U.S. Department of State, Overseas Security Advisory Council. Available at https://www.osac.gov/pages/ResourceLibraryDetails.aspx?cid=17609 . Last accessed April 2016.
  3. Jeffery K. Taubenberger et al. The pathology of influenza virus infections. Annu Rev Pathol. 2008;3:499- 522.
  4. Centre for Disease Control and Prevention, https://www.cdc.gov/flu/about/disease/symptoms.htm
  5. Chow A, et al. Emerg Infect Dis 2006;12:114-21
  6. MOH. Weekly Epidemiology Record. Available at https://www.moh.gov.sg/content/dam/moh_web/Statistics/ Infectious_Diseases_Bulletin/2016/March/2016_week_13.pdf. Last accessed April 2016
  7. Influenza (Seasonal). World Health Organization. Available at https://www.who.int/mediacentre/factsheets/fs211/en/. Last accessed April 2016
  8. MOH. Weekly Epidemiology Record. Available at https://www.moh.gov.sg/content/dam/moh_web/Statistics/Infectious_Diseases_Bulletin /2016/March/2016_week_13.pdf. Last accessed April 2016
  9. WHO Flunet, https://extranet.who.int/sree/Reports?op=vs&path=/WHO_HQ_Reports/G5/PROD/EXT/FluNetLaboratorySurveillanceData; accessed 20 Apr 2016

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