Darin Seehafer
Darin Seehafer
Clinical Scientist, PRA Vaccine Solutions

It’s October, and that typically means the beginning of the “flu season” in the U.S. While we can’t predict the timing, severity, or length of the season, we know for certain that flu spreads every year. Early reports coming out of the Southern Hemisphere indicate that this year’s influenza season is one of the worst in many years, which has the Northern Hemisphere on high alert for a potentially difficult season as well.

In Australia, reports have shown upwards of two and half times the normal number of infections seen over the previous year, with children between 5 and 9 years of age and adults over the age of 80 being the hardest hit. While it is not unusual to see spikes in influenza from year to year, the data is concerning.

According to Dr. Anthony Fauci, head of the National Institute of Allergy and Infectious Diseases (NIAID), "All the flu-ologists, myself included, say the only thing that you can predict about influenza is that it's going to be unpredictable." But, he adds, given what we are seeing the Australia, “An intelligent guess is that the north will probably have a bad flu season.”

In Australia, from the sentinel laboratories where influenza subtyping was undertaken (Tasmania, VIDRL and PathWest), influenza A (H3N2) was detected more frequently than influenza A (H1N1).

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Proportion of sentinel laboratory tests positive for influenza and total number of specimens tested, 1 January to 1 September 2017, by subtype and month and week.

How to Protect Yourself Against the Flu

An annual flu vaccine is the best way to protect yourself and your family from the flu. For the 2017-2018 season, the Centers for Disease Control (CDC) recommends use of the flu shot (inactivated influenza vaccine or IIV) or the recombinant influenza vaccine (RIV). The nasal spray flu vaccine, also known as the live attenuated influenza vaccine (LAIV), should not be used again during 2017-2018. The 2017-2018 influenza vaccination recommendations are available.

The CDC reports both good and bad news regarding last year’s vaccine (2016-2017); it appears circulating viruses were a close match to those contained in the vaccine; however, the vaccine’s effectiveness was only around 34% against type A (H3N2) and 56% against influenza type B viruses. This is in line with what has been seen over the past several seasons where vaccine effectiveness has been lower against type A (H3N2). However, routine universal immunizations still prevent significant morbidity and mortality. It is also important to understand how the predominant types shift throughout an influenza season, which can be seen in the table below from Blanton et.al.

Number and percentage of respiratory specimens testing positive for influenza reported by clinical laboratories, by influenza virus type and surveillance week — United States, October 2, 2016–May 20, 2017

When one considers the flu season just experienced in the Southern Hemisphere and the fact that Influenza A (H3N2) was the dominant type, along with the decrease in overall vaccine efficacy seen in Influenza A (H3N2) in both hemispheres, it is not hard to imagine that we may be in for a difficult influenza season as well in the north. The data also suggests that we can expect to see Influenza A (H3N2) as the dominant type early in the season.

The CDC recommends getting a flu vaccine early in the fall, before flu season begins, preferably by the end of October, if possible. Remember that it takes about two weeks after vaccination for antibodies to develop in the body to protect against flu. However, getting vaccinated later can still be beneficial. While flu activity often begins as early as October and November, the peak of the season in the U.S. is usually between December and February, but can continue as late as May.

Picture2 1

Number and percentage of respiratory specimens testing positive for influenza reported by clinical laboratories, by influenza virus type and surveillance week — United States, October 2, 2016–May 20, 2017

When one considers the flu season just experienced in the Southern Hemisphere and the fact that Influenza A (H3N2) was the dominant type, along with the decrease in overall vaccine efficacy seen in Influenza A (H3N2) in both hemispheres, it is not hard to imagine that we may be in for a difficult influenza season as well in the north. The data also suggests that we can expect to see Influenza A (H3N2) as the dominant type early in the season.

The CDC recommends getting a flu vaccine early in the fall, before flu season begins, preferably by the end of October, if possible. Remember that it takes about two weeks after vaccination for antibodies to develop in the body to protect against flu. However, getting vaccinated later can still be beneficial. While flu activity often begins as early as October and November, the peak of the season in the U.S. is usually between December and February, but can continue as late as May.

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