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CDC: Unprotected influenza strain prevalent; severe season expected
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The high prevalence of a drifted influenza A(H3N2) strain could lead to a worse influenza season, CDC Director Thomas R. Frieden, MD, MPH, announced today during a media briefing.
Ninety-one percent of approximately 1,200 influenza-positive tests reported to the CDC this year were influenza A virus, and 9% were influenza B, according to Frieden. Nearly all reported influenza A virus were H3N2, about half of which were antigenically different from the corresponding component included in the 2014 vaccine. This is a result of the drifted strain first being detected in March, Frieden said, after vaccine development had already begun.
Thomas Frieden
“Flu always has the potential to be serious, but H3N2 viruses tend to be associated with more severe seasons,” Frieden said during the briefing. “The rate of hospitalization and death can be twice as high or more than flu seasons where H3N2 doesn’t dominate. People with certain health conditions such as asthma, diabetes, heart disease, lung disease and pregnancy are also at high risk.”
Frieden still recommended that US citizens receive the current influenza vaccine for protection against the other included strains.
“If we have a severe season with H3N2 virus predominating, getting a vaccine — even if it doesn’t provide as good of protection as we would hope — would be more important than ever, and remains the single-most effective way to protect yourself against the flu,” Frieden said.
An influenza season without a highly effective vaccine means that antiviral medication will be especially important, he said. Treatment with antivirals can reduce illness duration and severity and is most effective when initiated within 48 hours of influenza symptoms. Despite this, prescription antivirals often are underprescribed.
“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,” Frieden said. “Probably fewer than one in six people who are severely ill with flu get antiviral drugs. It’s very important that we do better.”
Frieden also stressed that anyone infected with influenza should take steps not to infect others. This includes staying home from work or school when sick and using other basic sanitation practices.
Perspective
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William Schaffner, MD
Tighten your seat belts — it seems we’re in for a brisk influenza season, to say the least. Here are several ominous harbingers:
- The wily influenza virus has done it again — the A(H3N2) strain has mutated substantially, undergoing sufficient antigenic drift, and laboratory testing indicates that it is a poor match with the H3N2 antigen in this season’s vaccine. That portends poor protection from the vaccine against this strain.
- This new drifted H3N2 strain is already the dominant circulating viral strain, accounting for more than half the documented influenza cases early in the season.
- It has been the experience that H3N2 strains tend to produce more serious cases of influenza, resulting in more hospital admissions, more cases of pneumonia and more deaths.
- Influenza has started early and virtually over the entire country nearly simultaneously.
Taken together, these early indicators presage a serious influenza season. That said, what can we do?
- Keep using the flu vaccine. Recall that the vaccine is multivalent (either trivalent or quadrivalent), thus providing protection against the other strains that are circulating. Some protection is better than none.
- Promote good hand hygiene to provide a measure of personal protection and reduce the likelihood of transmission to others.
- Consider antiviral treatment when your patients become ill. This is especially important for patients who have risk factors for the pneumonic complications of influenza: older patients and those of any age who have underlying illnesses such as heart or lung disease, immunocompromise, diabetes and the like.
- Perhaps not widely applicable, but you could recommend relocation to the Southern Hemisphere for a month or more where they are having summer. Australian beaches, skiing in Chile … . Well, never mind, go back to suggestions 1,2 and 3, and do your best to stay healthy yourself!
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