The threat from influenza is not over. Only last week, two young people in Hong Kong were hospitalised in critical condition as a result of H1N1 flu, also known as 'swine flu'. Experts in Taiwan have also predicted that H1N1 flu could re-emerge in the island next month.
In Singapore, the number of acute respiratory infections (ARI) is reported to have hit epidemic levels, with a massive spike in patients seeking medical help.
The flu is a highly contagious viral infection that affects mainly the respiratory system - the nose, throat, and occasionally, the lungs. Most flu infections last for about a week, and have the following symptoms:
- Sudden high fever of over 38 degrees Celsius
- Nasal congestion (blocked nose)
- Chills and sweats
- Muscle aches (particularly in the back, arms and legs)
- Fatigue and weakness
At first glance, the symptoms of the flu may seem very similar to that of the common cold. A resource on the Mayo Clinic website says that one can differentiate between the two by the onset and severity of the symptoms: "Colds usually develop slowly, whereas the flu tends to come on suddenly. And although a cold can be a nuisance, you usually feel much worse with the flu."
In the past, one usually rested and hoped that the body's natural defenses will fight off the virus. Because the flu is caused by a virus, rather than bacteria, antibiotics are ineffective against it. However, with the development of new drugs that target viruses, people can now get treatment that may help reduce the severity of the flu.
Known as antivirals, these drugs have been used with some success in recent flu outbreaks.
Dr Tan Tze Lee, Chairman of the Singapore Primary Care Respiratory Group (SPCRG), shares with AsiaOne what antivirals are, and what people should know about them.
What are antivirals?
1. What are antivirals, and how are they different from antibiotics and vaccines?
Antivirals are the relative new kid on the block. Antiviral drugs are a class of medication used specifically for treating viral infections. Like antibiotics for bacteria, specific antivirals are used for specific viruses.
Unlike most antibiotics, antiviral drugs do not destroy their target pathogen; instead they inhibit their development.
Antiviral drugs are one class of antimicrobials - a larger group which also includes antibiotic, antifungal and antiparasitic drugs.
Vaccines are altogether different. Vaccines work to stimulate the immune system to make antibodies against the virus, i.e. the varicella vaccine, which is a weakened live virus, produces an antibody response to the varicella virus when it is injected into the body. This produces protection against chickenpox.
2. Who would benefit most from using anti-virals? When should patients ask for antivirals?
- Children younger than 2 years old;
- Adults 65 years of age and older;
- Persons with the chronic medical conditions: like asthma & COPD, cardiovascular (heart), diabetes mellitus, renal, hepatic, hematological etc.
- Women who are pregnant or within 2 weeks after delivery;
- Persons who are morbidly obese (body-mass index > 40);
- Residents of nursing homes and other chronic-care facilities.
If they have the symptoms of influenza and it is in the middle of the flu season, the likelihood that it is influenza will be high and they should ask for the antiviral treatment early with 48 hours of onset for it to be effective.
3. When should antivirals not be used?
Antivirals should not be used if one has an allergy to any of the components of the antiviral agent. In addition, in the case of oseltamivir (Tamiflu), it has to be prescribed with caution in patients with kidney or liver impairment, or hereditary fructose intolerance.
Tamiflu also has an interaction with clopidogrel (brand name Plavix - an antiplatelet medication to prevent blood clots), which may cause a decrease in Tamiflu's efficacy.
In the case of inhaled zanamivir (Relenza), it is generally advised not to use it if the patient has a history of underlying airway disease like asthma or COPD.
Both oseltamivir and zanamivir can cause inadequate immune response when intranasal live influenza vaccine (flu vaccine administered by a nasal spray) is administered, and so should be avoided. However as this form of vaccine is not available in Singapore, it is of little significance.
4. What are the risks / side effects of using antivirals?
Side effects differ for each antiviral drug.
Oseltamivir (Tamiflu): The most common side effects are nausea or vomiting. This usually happen in the first 2 days of treatment. Taking Tamiflu with food can reduce the chance of getting these side effects.
Zanamivir (Relenza): The most common side effects are dizziness, sinusitis, runny or stuffy nose, cough, diarrhea, nausea, or headache. It may also cause wheezing and trouble breathing in people with lung disease.
5. There have been reports of teens who developed suicidal tendencies after taking Tamiflu. When do the benefits clearly outweigh the potential risks?
Confusion and abnormal behavior leading to injury has been observed rarely in people with the flu who were treated with antivirals. Flu can also cause these behaviors. But persons taking these drugs should be closely monitored for signs of unusual behavior or problems thinking clearly. This behavior should be immediately reported to a health care provider.
6. There are reports that say that antivirals can lose their effectiveness against viruses if they are used widely. What is your comment on that?
The public should always have this at the back of their minds when they consider taking antivirals.
There have been reports of resistance to some of these medicines, some more, some less. It is important to use these medicines judiciously and responsibly.
I would say, keep the use of antivirals for when the symptoms are getting bad and if the patient is at risk of complications. The inhaled type zanamavir (Relenza) has on the other hand a rather low incidence of reported resistance.
7. Do you think that Singaporeans are at higher risk of getting influenza due to their frequent travelling? If so, how can they protect themselves?
Singaporeans are traveling overseas much more now than before, and as such are more likely to get influenza whilst abroad, especially during the influenza season.
If you are traveling overseas, whether it is for business or holiday, it is always a good idea to get yourself vaccinated with the influenza vaccine. This is now readily available from your local family doctor and will protect you against the 3 most prevalent influenza strains, i.e. H1N1 california 2009, H3N2 Perth 2009 and the Influenza B Brisbane 2008.
There are some who are unable to take the influenza vaccine due to egg allergy (flu vaccines are made using eggs) so these individuals should consider taking antivirals as prophylaxis (preventive medicine).
8 . Anti-virals are said to only be effective if taken within the first 24 hours of the onset of symptoms. However, the initial symptoms for influenza are similar to that of a cold - so how can the GP know whether an antiviral will be helpful or necessary?
Although the common cold and influenza are both upper respiratory illnesses, they are quite different. The common cold is rather milder than influenza.
In general, the flu is worse than the common cold, and symptoms such as fever, body aches, extreme tiredness, and dry cough are more common and intense.
Colds are usually milder than the flu. People with colds are more likely to have a runny or stuffy nose. Colds generally do not result in serious health problems, such as pneumonia, bacterial infections, or hospitalizations.
Usually during the flu season, like now, most influenza-like illnesses (ILI) will in fact be influenza.
One of the things we notice about patients with influenza is the sudden onset, fatigue and body ache, coupled with early respiratory symptoms.
9. If a patient has been having flu symptoms for several days already, will antivirals be of help?
These antivirals are most effective if taken within the initial 48 hours of the infection. However some studies have shown there to be some benefit in alleviating the symptoms even when taken after 48 hours.
10. If one has mild symptoms of respiratory infection, should one ask for antiviral medication, or would it be better to just allow the body to fight off the illness on its own and thus 'acquire immunity' in the process?
If the symptoms are mild, there is no need to take antivirals. However as mentioned before, if one is in the high risk groups indicated above, then antivirals should e considered.
11 . What is the effect of antivirals on our immune system? Does it weaken it or compromise it in any way?
These antivirals do not affect our immune system per se.
It is important not to confuse them with antibiotics, which are different. Indiscriminate use of antibiotics encourage antibiotic resistance in bacteria which make conventional antibiotics ineffective.