The 2014-2015 flu season may be particularly severe, and the 2014-2015 vaccine will provide important, but limited protection, according to a health advisory from the Centers for Disease Control and Prevention that is based on early analyses of reported disease cases.
The advisory also stresses the importance of antiviral treatment in those with confirmed or suspected influenza, particularly those at risk of developing complications, including young children, adults aged 65 years and older, pregnant women, and those with chronic health conditions, such as asthma, diabetes, or heart, lung, or kidney disease.
Influenza A viruses, mainly H3N2, predominate thus far during the 2014-2015 flu season, comprising more than 91% of the specimens collected and analyzed, and only about half of those have been antigenically similar to H3N2 components included in the 2014-2015 vaccine, according to the advisory.
This doesn’t bode well for the effectiveness of the vaccine, which is particularly troubling given that H3N2-predominate seasons historically have been associated with up to twice the rate of overall and age-specific flu-related hospitalizations and deaths, CDC director Dr. Thomas R. Frieden explained during a press briefing.
Still, vaccination remains the best line of defense against infection, he said.
The vaccine will protect against circulating strains that have not undergone significant antigenic drift, including the influenza B viruses, which have comprised about 9% of those collected to date. In addition, the vaccine has been found to provide some protection against the antigenically drifted H3N2 viruses, he said.
“We continue to recommend flu vaccine as the single best way to protect yourself against the flu,” he said.
Dr. Frieden also stressed the importance of antiviral use.
“Antivirals aren’t a substitute for vaccinations … but they are an important second line of defense for treating the flu, and this year, treatment with antiviral drugs is especially important, particularly for people who are at high risk for serious flu complications or for people who are very sick with flu,” he said.
These agents are greatly underprescribed, with fewer than one in six severely ill patients receiving antiviral treatment, he noted.
“It’s very important that we do better for people who are severely ill or who could become severely ill with influenza,” he said, adding that antiviral use is even more important during seasons such as this one when the circulating viruses are different from the vaccine viruses.
The two neuraminidase inhibitor antiviral medications currently approved for treating influenza – oseltamivir and zanamivir – shorten the duration of fever and illness symptoms by about a day and can reduce the risk of severe outcomes, he said.
Treatment should be provided withing 2 days of symptoms onset when possible, but it may also provide benefit to hospitalized patients even if taken later in the course of illness.
“We strongly recommend that if doctors suspect the flu in someone who may be severely ill from the flu, they don’t wait for the results of a flu test before starting antivirals,” he said.
“There is no way to predict with certainly what will happen. We have four different strains of flu circulating. The B strain, the H1 strain, the well-matched H3 strain, and the poorly matched H3 strain. Only time will tell which of them, if any, will predominate for the coming weeks and months of this year’s flu season,” he said.
However, already this season there have been five pediatric deaths from influenza, including three in patients with H3N2 disease, and one in a patient with influenza type B.
“We’ve also heard of outbreaks in schools and in nursing homes,” Dr. Frieden said, adding that “getting a vaccine, even if it doesn’t provide as good protection as we would hope, would be more important than ever, and remains the single most effective way to protect yourself against the flu.”
Physicians should continue to vaccinate patients, he said, noting that nearly 150 million doses have been distributed by manufacturers, and that the supply is expected to meet the demand. The supply of antiviral medications is also expected to be adequate.
Patients should also be advised to stay home when they are sick to avoid spreading influenza, and to seek treatment promptly for flu symptoms, including fever, cough, sore throat, runny or stuffy nose, body aches, headache, chills, and fatigue, he said.