<P> The antiviral drugs amantadine and rimantadine inhibit a viral ion channel (M2 protein), thus inhibiting replication of the influenza A virus . These drugs are sometimes effective against influenza A if given early in the infection but are ineffective against influenza B viruses, which lack the M2 drug target . Measured resistance to amantadine and rimantadine in American isolates of H3N2 has increased to 91% in 2005 . This high level of resistance may be due to the easy availability of amantadines as part of over-the - counter cold remedies in countries such as China and Russia, and their use to prevent outbreaks of influenza in farmed poultry . The CDC recommended against using M2 inhibitors during the 2005--06 influenza season due to high levels of drug resistance . </P> <P> Influenza's effects are much more severe and last longer than those of the common cold . Most people will recover completely in about one to two weeks, but others will develop life - threatening complications (such as pneumonia). Thus, influenza can be deadly, especially for the weak, young and old, those with compromised immune systems, or the chronically ill . People with a weak immune system, such as people with advanced HIV infection or transplant patients (whose immune systems are medically suppressed to prevent transplant organ rejection), suffer from particularly severe disease . Pregnant women and young children are also at a high risk for complications . </P> <P> The flu can worsen chronic health problems . People with emphysema, chronic bronchitis or asthma may experience shortness of breath while they have the flu, and influenza may cause worsening of coronary heart disease or congestive heart failure . Smoking is another risk factor associated with more serious disease and increased mortality from influenza . </P> <P> According to the World Health Organization: "Every winter, tens of millions of people get the flu . Most are only ill and out of work for a week, yet the elderly are at a higher risk of death from the illness . We know the worldwide death toll exceeds a few hundred thousand people a year, but even in developed countries the numbers are uncertain, because medical authorities don't usually verify who actually died of influenza and who died of a flu - like illness ." Even healthy people can be affected, and serious problems from influenza can happen at any age . People over 65 years old, pregnant women, very young children and people of any age with chronic medical conditions are more likely to get complications from influenza, such as pneumonia, bronchitis, sinus, and ear infections . </P>

What is the name of the virus that causes influenza