Flu and Cold

​Influenza, also known as the “flu” is a contagious disease that is caused by the influenza virus. It commonly attacks the respiratory tract of human (nose, throat and lungs). Unlike common cold, flu may cause severe illness and life-threatening complications in some people.

Influenza is an illness that can come on suddenly and may include the following symptoms:

• Fever
• Headache
• Tiredness (can be extreme)
• Dry cough
• Sore throat
• Nasal congestion
• Body aches

Occasionally, some patients and children may also suffer from gastro-intestinal symptoms, including nausea, vomiting and diarrhoea.

Some of the complications include secondary bacterial pneumonia, dehydration, and myocarditis. Flu may also worsen some pre-existing chronic medical conditions, such as congestive heart failure, asthma, or diabetes.

Children may get sinus and ear infections as complications from the flu. The elderly and those with chronic medical conditions are at highest risk for developing serious complications.

It is sometimes difficult to tell the difference between the flu and other viral diseases based on symptoms alone. Tests may help to confirm or exclude that an illness is influenza or other viral illnesses. In addition, a doctor’s assessment is important to determine whether someone has complications resulting from the flu.

The Influenza virus causes the flu. There are 3 types of Influenza viruses- Types A, B and C Influenza. Types A and B viruses cause epidemics of disease. Influenza Type C usually causes a mild respiratory disease and are not thought to cause epidemics.

A flu vaccination can prevent illness from certain strains of Influenza Types A and B depending on the yearly composition but does not protect against Type C.

Influenza A viruses are found in many animals, including ducks, chickens, geese, pigs, wild birds, whales, horses, and seals. Wild birds are the primary natural reservoir for all subtypes of influenza A viruses and are thought to be the source of influenza A viruses in all other animals. Influenza B viruses circulate widely only among humans.

While it is unusual for people to get influenza infections directly from animals, human infections and outbreaks caused by certain animal influenza viruses have occasionally been reported.

In 1997 and early 2003, human infections with bird or avian influenza A (H5N1) virus were reported by Hong Kong Department of Health. The World Health Organization (WHO) also announced a global swine flu (H1N1 pandemic) during the period of 11th June 2009 till 10th August 2010. Although H1N1 is no longer the dominating flu strain, it will not disappear altogether. Rather, it would be seen as behaving more like the seasonal flu activity.

​Influenza A viruses are divided into “subtypes” based on 2 proteins on the surface of the virus: the hemagglutinin (H) and the neuraminidase (N). There are 15 different “H” subtypes and 9 different “N” subtypes. A combination of different “H” and “N” proteins on the surface of the influenza virus describes different types of influenza A viruses.

Many people use the term “Stomach Flu” to describe illnesses with nausea, vomiting, or diarrhoea. Many different viruses, bacteria or even parasites can cause these symptoms. While vomiting, diarrhoea and being nauseous can sometimes be related to the flu, particularly in children, these problems are not commonly the main symptoms of influenza.

For healthy individuals, seasonal influenza is usually a self-limiting illness with recovery in 2-7 days.

Medications for symptomatic relief such as decongestants, cough remedies, and simple pain relievers including paracetamol can help you feel better while your body's immune system fights off the infection. Antiviral medications e.g. oseltamivir (marketed as TAMIFLU®), if started in the first two days after your symptoms start, can shorten the length of your illness. These will need to be prescribed by your doctor depends on disease severity and other risk assessments.

Since seasonal influenza is a viral infection, antibiotics would not be effective unless the flu is complicated by bacterial infection, such as pneumonia, sinusitis or ear infection.

A number of tests can help to diagnose influenza. These tests include taking samples from a throat swab, nasal wash or nasal aspirates and are done within the first 3- 4 days of your illness. Rapid Diagnostic Tests for Influenza (RIDTs) can be conducted in clinic and results can be obtained in as fast as 15 minutes with accuracy up to 90% or higher*. These tests are useful when a doctor needs additional information to help determine diagnosis and treatment decision.

*Reference: CAPILIATM Flu Neo (manufactured by TAUNS Laboratories, Inc. Japan) Product Information.

You are recommended to do the following:

• Rest
• Drink plenty of fluids
• Avoid using alcohol and tobacco (e.g. cigarettes and cigars)
• Take medication to relieve the symptoms of flu
• Seek medical advice if there is high fever, if you or your family members have chronic medical conditions, if the member of the family is very young or elderly, or if you suspect complications of influenza

Influenza is caused by a virus, so antibiotics would not help unless you develop a secondary bacterial infection.

The time from when a person is exposed to flu virus to when symptoms begin is about 1-4 days, with an average of about 2 days.

​In Hong Kong, influenza is most prevalent in January-March and July-August.

The flu is transmitted, or spread, when a person who has the flu coughs, sneezes, or spits, thus sending the droplets with flu virus into the air, where other people may inhale the virus. The virus then enters the nose, throat, or lungs of a person and begins to multiply, causing symptoms of influenza.

Influenza may also be spread when a person touches a surface that has flu viruses on it- such as a door handle - and then touches his or her nose or mouth.

A person can spread the flu even one day before he or she feels sick. Adults can continue to pass the flu virus to others for another 3 to 7 days after symptoms start. Children can pass the virus for longer than 7 days.

Symptoms start 1 to 4 days after the virus enters the body. Some persons can be infected with the flu virus but have no symptoms. During this time, those persons can still spread the virus to others.

The best way to prevent the flu is to get an influenza vaccine (flu shot) before the flu season. A yearly flu shot is recommended for the following groups of people who are at increased risk for serious complications from or transmission of the flu:

• Persons aged >50 years
• Children aged 6 months to 5 years
• Residents of nursing homes and other long-term care facilities that house persons of any age who have long-term illnesses
• Adults and children > 6 months of age who have chronic heart or lung conditions, including asthma
• Adults and children > 6 months of age who need regular medical care or had to be in a hospital because of metabolic diseases (like diabetes), chronic kidney disease, obese individual with body mass index > 30, or weakened immune system (including immune system problems caused by medicine or by infection with human immunodeficiency virus or HIV)
• Children and teenagers (aged 6 months to 18 years) who are on long-term aspirin therapy and therefore could develop Reye’s Syndrome after the flu
• Pregnant women at all stages
• Healthcare workers and other workers in a healthcare work environment including clinics, hospitals and elderly homes
• Poultry workers, pig farmers and pig-slaughtering industry personnel

The following are suggested ways to prevent catching the flu virus:

• Maintain good personal and environmental hygiene
• Keep hands clean and wash hands properly
• Wash your hands when there are respiratory secretions on them, e.g. after sneezing.
• Cover your nose and mouth while sneezing or coughing and dispose of nasal and mouth discharge properly. Do not spit.
• Good body defense helps to prevent influenza infection. This can be achieved through a balanced diet, regular exercise, adequate rest, reduced stress and avoid smoking.
• During the “flu season”, it is better to avoid crowded public places where the ventilation is not good.
• By far the best way to prevent the flu is for individuals, especially for those at high risk, to get a flu shot each year.

Yes there is a vaccine. It is referred to as an influenza vaccine or a flu shot. The influenza vaccine is prepared according to the strains prevalent in the community each year, as recommended by the World Health Organization. There are trivalent and quadrivalent flu vaccine available.

The trivalent flu vaccine is designed to protect against three different flu viruses: two influenza A viruses and one influenza B virus. The quadrivalent flu vaccine is designed to protect against four different flu viruses: two influenza A viruses and two influenza B viruses.

For years, flu vaccines were designed to protect against three different flu viruses (trivalent). This included an influenza A H1N1 virus, an influenza A H3N2 virus and one B virus. Experts had to choose one B virus, even though there are two very different lineages of B viruses that both circulate during most seasons. This meant the vaccine did not protect against the group of B viruses not included in the vaccine. Adding another B virus to the vaccine aims to give broader protection against circulating flu viruses.

The flu vaccine is 70-90% effective in preventing influenza among healthy adults if it is administered at least 2 weeks before exposure and if there is a good match between the vaccine and the influenza strain causing illness. Vaccine effectiveness is lower for older persons, but can significantly reduce their chances of serious illness or death from influenza.

Anyone who wants to lower his or her chances of getting the flu can get a flu shot. In particular, people at high risk for complications of the flu and people in close contact with them (including household members) should get the vaccine. The Scientific Committee on Vaccine Preventable Diseases under the Centre for Health Protection (CHP) of the Department of Health recommends seasonal influenza vaccination for personal protection against clinical influenza for all persons except those with known contraindications. Moreover, nine categories of people are recommended to receive vaccination against seasonal influenza:

• Pregnant women at any gestational stage
• Elderly persons living in residential care homes
• Long-stay residents of institutions for the disabled
• Persons aged 50 years or above
• Persons with chronic medical problems including those obese individual with BMI>/=30
• Health care workers
• Children aged 6 months to 11 years
• Poultry workers
• Pig farmers and pig-slaughtering industry personnel

Pregnancy can alter the immune system, and affect a mother’s cardiovascular and respiratory function (heart and lung function). These changes may place a pregnant woman at increased risk of developing complications from the flu. One study showed that amongst the pregnant women, the group who did not receive flu vaccination is 22 times more likely to suffer from complication of flu than the group who had received flu vaccination.

Because the flu shot is made from inactivated viruses (the viruses are killed), many experts consider flu shots safe during pregnancy. According to the recommendations from the World Health Organization (WHO), the Centers for Disease Control and Prevention (CDC) of United States as well as from the Centre for Health Protection (CHP) of Hong Kong, inactivated influenza vaccine can be used for all stages of pregnancy. There is no evidence indicating inactivated influenza vaccine is teratogenic.

As it takes 2 weeks for antibodies to develop after vaccination, all pregnant women are recommended to get a flu shot before the flu season, especially for those who have medical problems that increase their risk for complications from the flu.

It is safe to get a flu shot even if you are breastfeeding.

The following groups should not get a flu shot before consulting with their doctor:

• People who have severe allergy to eggs (ovalbumin and chicken protein). This includes individuals who develop swelling of the tongue, lips or experience acute respiratory distress or collapse after ingestion of eggs.
• People who have had a severe reaction to a flu shot in the past
• People who have previously developed Guillain-Barre Syndrome (GBS) in the 6 weeks after getting a shot (a disease of the nervous system resulting in muscle weakness or paralysis)
• People with known allergy to Gentamicin Sulphate or any other excipients of the vaccine - Polysorbate 80, Octoxinol 10, Haemagglutinin, Sodium Deoxycholate, Cetyltrimethylammonium Bromide, Octylphenol Ethoxylate and Formaldehyde.
• People with a moderate to severe acute illness, with or without fever.
• People with problems with immune system as the immune response may be diminished.

Flu viruses change from year to year. Because of this, you need to be aware of the following:
 

The natural protection or immunity you develop after catching a particular strain of influenza virus does not necessarily protect you against another strain of influenza virus.
 

Secondly, a vaccine made against one flu virus may not protect you against a different strain. That is why the influenza vaccine is updated each year to include current strains of the year.
 

A third reason to get influenza vaccination every year is that after you get a flu shot, your immunity to the flu declines over time and may not provide adequate protection after one year.

Flu vaccinations for the year generally become available in the second half of the year, before winter arrives in the Northern Hemisphere.

Once you get a flu shot, it takes about 2 weeks for antibodies to develop in the body and provide you with protection against influenza virus infection. In the meantime, you are still at risk of catching the flu. That is why it is much better to get vaccinated before the flu season starts.

Yes. The ability of an influenza vaccination being able to protect a person depends on

2 things:

• The age and health status of the person getting the vaccination and
• The similarity or “match” between the virus strains in the vaccine and those viruses in circulation.
   

When the “match” between the vaccine and the circulating strains of viruses is close, the flu vaccine prevents influenza in about 70-90% of healthy persons younger than age 65 years.

Influenza vaccine only protects against illness caused by influenza viruses, and not against other conditions such as fever, colds or gastrointestinal complaints caused by other viruses.

​The influenza vaccine is made from inactivated or killed flu viruses, and does not cause flu illness.

• Soreness, redness, or swelling where the injection was given
• Fever (low grade)
• Aches

These problems may occur soon after the injection and should usually last no more than 1 to 2 days.

Life-threatening allergic reactions are rare. These reactions tend to occur among persons with a severe allergy to eggs, because the viruses used in the influenza vaccine are grown in chicken eggs. People who have had a severe reaction to eggs or to flu shot in the past, should not be vaccinated before consulting a doctor.
 

Guillain–Barré syndrome (GBS) - This condition is characterised by fever, nerve damage and muscle weakness. A study done in 1976 suggests that 1 out of 1 million vaccinated persons may be at risk of GBS associated with the vaccine. Most people eventually recover, but some may have permanent nerve damage.

The most frequently reported adverse events were local discomfort at injection sites and headaches. For Guillain–Barré syndrome, there was no direct link found with the flu vaccine in most cases. There is also no evidence that flu vaccine leads to fetal losses.
 

Locally, the Centre for Heath Protection has monitored the significant adverse events of seasonal influenza vaccination and the details can be found at the following link:

http://www.chp.gov.hk/en/view_content/14843.html

Rapid diagnostic tests for influenza (RIDTs) can identify different kinds of influenza A and B viral infections. Doctors will collect a nasal swab specimen for screening. RIDTs can detect influenza viral antigens even at an early stage of infection and take only 15 minutes to give the results.

In fact, it is difficult to distinguish influenza from illnesses caused by other viruses simply by symptoms. If necessary, patients can take the rapid test to identify whether they have any influenza infection and eliminate the possibility of having other viral infections. The test is meant to facilitate accurate diagnosis and make good use of the 48-hour golden period for treatment to reduce the risk of complications.