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Why the Flu Vaccine Barely Worked This Year

Mutating strains stay one step ahead of vacccine-makers

The Centers for Disease Control and Prevention (CDC) estimates that this year’s influenza vaccine was only 18% effective against the dominant H3N2 strain of the flu in circulation, according to a report on the BioSpace website. This is down from previous estimates that the vaccine was 23% effective.

The injected vaccine for children between 2 and 8 years of age was even worse, with an effectiveness rate of only 15%, and the nasal-spray version may not protect young children at all, according to the CDC.

The flu vaccine market showed signs of growth at the onset of this year’s flu season, when companies expected to ship about 160 million doses of the vaccine for the U.S. market, compared with nearly 135 million doses produced last season, according to the CDC. Sanofi Pasteur, the largest distributor of the flu vaccine in the U.S. and the maker of Fluzone, announced plans to supply at least 65 million doses this season. Novartis planned to ship 30 million doses of two flu vaccines: Flucelvax and Fluvirin. GlaxoSmithKline planned to ship about 28 million doses. Other makers, such as MedImmune, maker of FluMist, planned to ship between 14 million and 15 million doses, while Protein Sciences, maker of the recombinant egg-free vaccine Flublok, planned to supply around 500,000 doses.

Despite the growing supply, flu vaccines fell short when it came to protecting against this year’s dominant strain. The vaccines’ 18% effectiveness rate was the lowest the CDC has seen since it began tracking effectiveness in 2004–2005, when the rate was at 10%. Since then, effectiveness rates have fluctuated between 20% and 60%, with the strongest year (60%) occurring in 2010–2011. Last year, the vaccine was 51% effective.

“These numbers, which are lower than we normally see, are because the flu viruses that are circulating have mutated to look very different than the vaccine strains,” said Dr. Joseph Bresee, of the CDC’s National Center for Immunization and Respiratory Diseases.

The H3N2 flu strain wasn’t factored into this season’s vaccine, which takes approximately 4 months to make. The strain was seen for the first time in March 2014, while the World Health Organization’s (WHO) procedures and decisions regarding which strains to include in the vaccine were made a month earlier in February. The decision is finalized before the beginning of the next year’s flu season to account for production and distribution time.

In fact, an FDA advisory committee recently endorsed the WHO’s choice of flu strains for the 2015–2016 seasonal flu vaccine. The WHO recommended changing two of the three strains in trivalent flu vaccines for the next Northern Hemisphere flu season: H3N2 and influenza B. The FDA’s Vaccines and Related Biological Products Advisory Committee unanimously approved the WHO’s H3N2 selection, which was widely expected since most of the circulating H3N2 viruses in the U.S. and in several other countries did not match well with the vaccine this year.

The flu strain selection process gets more complicated when one considers that each year new strains can emerge and mutate and are therefore unpredictable. Unlike the measles vaccine, which is relatively straightforward since there is only one antigenic type of measles virus, there are hundreds of different strains of influenza to mull over when trying to create a vaccine.

“Once vaccine production commences, it is not possible to change the chosen vaccine strains if a drift is detected,” Polina Miklush, a spokesperson for Novartis, told BioSpace.

Meanwhile, the public is questioning the necessity of the flu vaccine more than ever before. In this year’s early flu season (November 2014), 42% of children and nearly 40% of adults were vaccinated. In comparison, 51% of children and 40.5% of adults were vaccinated in 2010.

The CDC recommends that everyone aged 6 months and older get vaccinated. In addition, the agency suggests taking precautions, such as early treatment with antiviral drugs such as Tamiflu and Relenza, along with washing hands frequently and covering the mouth when coughing or sneezing.

Meanwhile, scientists are trying to devise a strategy for a more-effective vaccine. They are looking for antigens that correspond to the parts of the virus that stay the same, even when the rest of the virus has changed. A flu vaccine developed by scientists at Okairos, a company based in Rome, Italy, that is pioneering the development of T-cell–based vaccines for infectious diseases, for example, was tested at the FDA and showed potential as a “universal” vaccine to protect against a broad range of flu viruses.

Source: BioSpace; April 1, 2015.

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