Wednesday, March 14, 2018

Influenza 2017-2018: A review of the flu virus and vaccine effectiveness

By Jasmeet Kaur, MD
Austin family physician

Have you had your flu vaccine yet?

It’s a simple yet essential part of your annual doctor visit. The influenza virus causes the flu. Flu symptoms include upper/lower respiratory tract symptoms, runny nose, cough, headache, fever, chills, and body aches. By vaccinating against the flu, you can significantly decrease your chance of getting the illness, or lessen the severity of the illness. Other ways to minimize chances of getting the flu are washing hands frequently, avoiding touching your nose/mouth/eyes, cleaning commonly touched surfaces frequently, and avoiding shaking hands with or coming in close contact with others who are ill. To prevent spreading germs, cover coughs and sneezes, and stay home if sick.

Flu season in the United States peaks from December to February; however, the virus circulates year-round. Influenza is responsible for millions of illnesses, hundreds of thousands of hospitalizations, and tens of thousands of deaths yearly.

The flu is spread through droplets from coughing, sneezing, or talking, which land in the mouths, noses, or lungs of nearby individuals up to six feet away, or directly when someone touches a surface or object with flu virus on it. The flu starts being contagious one day before symptoms develop and lasts up to five to seven days after the person becomes sick. This means people can spread the illness before realizing they are sick.

Most individuals with mild illness recover in less than two weeks and do not need medical care or antiviral drugs. Flu-related complications include pneumonia, bronchitis, or sinus infections. These groups of people have the highest risk for flu-related complications: children younger than 5 years old (particularly children under 2 years old), adults over 65 years old, pregnant women to two weeks postpartum, nursing home/long-term facility residents, and Native Americans. People with particular medical conditions such as chronic diseases, diabetes, and weakened immune systems also may be more susceptible to flu-related complications. In the current flu season, during the last week of December, 8.2 percent of the people in the United States suffering from influenza and pneumonia died from it. The Centers for Disease Control and Prevention (CDC) calls that epidemic. In previous years, as many as 7.1 percent of patients died.

You might have heard about “type A flu,” or “H1N1.” What do these names mean? Scientists divide the influenza virus into types A, B, and C, and subtypes H1, H2, H3, N1, and N2 based on differences in the virus’ makeup. Influenza A leads to annual local outbreaks, epidemics every two to three years, and even occasional pandemics. In comparison, influenza B causes milder disease, with outbreaks occurring every four years. Seasonal influenza C usually causes mild disease and is generally not responsible for epidemics or pandemics. (A disease outbreak means more people are sick than expected in a community or region or during a season; an epidemic means the disease spreads rapidly to many people; and a pandemic is worst of all because it means a worldwide disease outbreak.)

Influenza viruses are constantly changing and mutating. Small mutations are responsible for seasonal influenza viruses and require a new vaccine with each annual influenza season. Larger mutations can result in pandemics.

CDC analyzes and monitors nearly 2,000 influenza viruses every year to help determine which strains should be included in the upcoming season’s influenza vaccine. Despite the close monitoring, there are limitations to the vaccine’s creation. One reason is there is a lag of six to eight months between when current influenza strains are identified and when influenza vaccines are manufactured in large amounts; during that lag the virus can further mutate, resulting in a poor vaccine match for the current circulating strain.

By mid-January, CDC pointed to the influenza A (H3N2) virus subtype as this season’s most common culprit. By then, the season’s vaccine had been mass-produced and distributed, and even given to millions of people. Unfortunately, it was not a perfect match for this year’s virus. Early predictions give this year’s flu vaccine a 33-percent overall effectiveness against influenza and a 10-percent effectiveness against the H3N2 strain. Regardless of the limitations of the vaccine, it remains one of the best ways to reduce one’s chances of getting the disease, or reduce the severity of the disease. And for those who do get sick from the flu, antiviral medications such as oseltamivir, zanamivir and peramivir (better known by brand names like Tamiflu) can make the illness less severe and shorter.

Bottom line: Make sure next time you go to your doctor you are able to say, “Yes, I received my flu shot this year!”

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