Influenza vaccination still advised despite drifts

This article was originally published in the Le Mars Daily Sentinel. Printed with permission.

An influenza virus strain has emerged in the United States that differs from the one health officials predicted would appear during the flu season. Both strains are subtypes of the A(H3N2) virus, but the newer one is not fully covered by this year's influenza vaccination.

Clinical lab analysts Kris Eveland (foreground) and Erik Twait prepare specimens for influenza testing at the State Hygienic Laboratory at the University of Iowa, in Coralville. The laboratory receives specimens from hospitals and clinics throughout the state. Lab analysis helps reveal prevalent strains of flu circulating in Iowa.

About half of A(H3N2) cases reported to the Centers for Disease Control and Prevention, or CDC, are associated with the new strain.

The virus has changed, or "drifted," from the A(H3N2) strain CDC officials predicted would be most prevalent.

Cases have not been confirmed in Iowa, according to the Iowa Department of Public Health.

Although the drifted strain is not included in this year's flu vaccine, CDC officials advise health providers to encourage unvaccinated patients to receive the vaccine.

There is a good reason why individuals are advised to receive a flu vaccination every year, said Dr. Wade Aldous.

Aldous is the director of the Disease Control Division at the State Hygienic Laboratory at the University of Iowa in Coralville.

Influenza viruses are constantly changing each time they replicate, he said. Those small genetic changes add up and can alter the virus' properties.

"If you think about when you were younger and had to play the 'telephone' game -- you had to whisper a message to somebody next to you," Aldous said.

During the game, each person whispers the message he hears to an adjacent person. Each time a message is repeated, small changes can occur if the receiver does not hear it clearly.

"About 30 people later, that message came out a little bit garbled," Aldous said. "That's similar to what happens each time a flu virus replicates," he said. After a person is infected with a flu virus, his immune system will produce antibodies that recognize the virus and help neutralize it, preventing further infection.

But as a flu virus changes, antibodies eventually will cease to recognize it. That means a person can be reinfected with the flu from the drifted virus.

There is another way the flu virus can change. It is called a viral "shift." A shift is when actual pieces of the virus' structure change, creating a very different flu virus. Most people do not have immunity to the new virus.

"A shift is something you do not want to have," Aldous said. He noted a recent example of a viral shift concerned avian influenza, often called "bird flu." That flu virus, an A(H5N1) virus, was only found in birds before it jumped species and infected a small number of people. That particular virus did not spread among the general population, but flu viruses that shift are still cause for concern, said Aldous.

"We could be very much in trouble by being exposed to these things because we've never seen them before. Our bodies are naive," he said. What happened to this year's flu virus was a drift, not a shift, said Aldous.

"It stays the A(H3N2), but it has a little bit of a mutation along the way," he explained. To be effective, vaccines have to protect against viruses that have drifted and shifted. Determining which flu strain a vaccine should protect against is an annual process, said Aldous.

Magnified under an electron microscope and digitally colored, H1N1 influenza virus particles are visible. This year's flu vaccination protects individuals against a particular strain of H1N1, but may have limited effectiveness against an H3N2 flu virus that is circulating throughout the country. (Photo contributed)

To detect and develop vaccines to prevent the flu, the CDC monitors reported influenza cases nationwide. In Iowa, analysts at the State Hygienic Laboratory study specimens submitted from hospitals and clinics. Testing at the lab determines what strain of influenza virus a specimen contains.

"We send that (information) off to the Centers for Disease Control, and they collect that data and data submitted by other state public health laboratories," said Aldous. In conjunction with the World Health Organization, the CDC identifies the prevailing strains of influenza observed at the height of the flu season.

"It helps them to determine what are the best choices to use for the following year's vaccine," Aldous said.

In the United States, the peak of flu season is typically in January and February. It takes about six to nine months to prepare vaccines, which are usually available by the middle of October.

"It's not something you can just do overnight," he noted. "That's why they have to determine around the middle of February what vaccines they must include in the next year's formulation." Scientists select the most prevalent flu strains at the peak of flu season for the vaccine because they are the most likely strains to appear during the following flu season, Aldous said.

Sometimes viruses will have drifted by the time a vaccine is available for use. Mutations in this year's A(H3N2) virus were not detected until after the peak of flu season and the 2014-2015 flu vaccine's formulation was already selected, Aldous said. This year's flu vaccine will have limited protection against the drifted strain, he said.

"It is very good and it does offer protection, especially for those people that are immunosuppressed," Aldous noted.

Health officials also recommend elderly individuals, healthcare personnel and people who have close contact with children younger than 6 months receive the flu vaccine. Doing so might reduce the likelihood of severe outcomes of infection, including hospitalization and death, according to the CDC.

Although A(H3N2) has drifted, this year's vaccine offers protection against influenza A(H1N1) and two influenza B virus strains. Additionally, those who are infected with any strain of the flu this season, including A(H3N2), have the option of antiviral medication. Clinical studies have shown that antiviral treatment can reduce complications from influenza and shorten the duration of symptoms.