Massachusetts health authorities are preparing for a worse flu season than usual after the US Centers for Disease Control and Prevention said Thursday the flu vaccine is not well matched to the severe Type A flu strain in widespread circulation.
“Without a good match, we know the vaccine will be less effective at preventing transmission of influenza,” said Dr. Alfred DeMaria, state epidemiologist at the Massachusetts Department of Public Health. “We also worry about severe influenza whenever it’s a Type A season” because those strains tend to cause more serious symptoms, including breathing difficulties that result in hospitalizations.
About 90 percent of flu strains circulating in late November and analyzed by the CDC were Type A strains, Dr. Tom Frieden, the CDC director, said in a press briefing. Half of those had mutated and did not match the H3N2 strain present in the vaccine, which also contains two or three other flu strains.
Frieden added, though, that “there’s no way to predict with certainty exactly what will happen, and only time will tell which strain will predominate for following weeks and months of flu season.”
DeMaria, an infectious disease expert, said the new H3N2 strain would likely predominate because people have little immunity to it and will spread more easily than the other strains included in the vaccine.
The new strain was first detected in March, which was too late to be included in the seasonal shot produced every year by vaccine manufacturers.
Public health officials emphasized that getting a yearly flu shot remained the best way to prevent the virus in those ages 6 months and older.
“The vaccine will protect against other strains that are circulating including half of the Type A strains,” said Dr. Anita Barry, infectious disease bureau director at the Boston Public Health Commission.
It might also provide a little protection against the new strain, causing less severe symptoms in those who had the shot, DeMaria said.
The flu vaccine was about 60 percent effective last year, when circulating strains were well matched to the shot, but effectiveness tends to vary from year to year.
At least twice during the past decade, strains contained in the shot did not match the strain predominantly circulating, DeMaria said.
In an advisory sent to the medical community Wednesday night, the CDC recommended that doctors be especially vigilant in treating flu symptoms in high-risk populations such as the elderly, young children, pregnant women, and patients with asthma. heart disease, or compromised immune systems.
These groups are more likely to die of flu complications and are typically prescribed antiviral drugs.
“It’s very important that we do better for people who get severely sick with influenza,” Frieden said. “Only one in six people who have severe flu take antiviral drugs to combat their symptoms.”
Antivirals work best when started within two days of flu symptoms, but they are also recommended for anyone hospitalized with flu symptoms.
They shorten the duration of flu symptoms by about a day, Frieden said. Studies indicate the drugs lower the risk of pneumonia and death in those hospitalized with influenza.
There are two FDA-approved influenza antiviral drugs recommended by the CDC for this year’s seasonal flu: Tamiflu (oseltamivir) and Relenza (zanamivir).
Tamiflu is available as a pill or liquid, and Relenza comes as a spray that is inhaled.
Five children have died in the United States from influenza so far this flu season, which has barely gotten underway. The CDC did not identify which strains the children had, nor whether they were vaccinated.
An estimated 3,000 to 49,000 people in the United States die from the flu every year depending on the severity of the flu season, according to the agency.
“We’ve had fewer than 20 influenza cases in the past few weeks,” Barry said. “We’re not seeing a lot of activity in emergency departments right now.”
Beyond getting vaccinated, she recommended that residents use personal protection measures to avoid getting and spreading the flu such as washing hands frequently, staying home when sick with fever, and avoiding close contact with anyone who has symptoms.
Unlike cold viruses that cause symptoms with a gradual onset, flu symptoms usually come on suddenly with a fever, chills, cough, and sore throat.
Those who develop such symptoms should call their doctor to determine whether they could benefit from a prescription for antiviral medications, Barry recommended.