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Anticipating a Severe Flu Season

Amesh A. Adalja, MD, FACP, FACEP, FIDSA, October 20, 2017

While the flu season in this hemisphere has yet to fully commence, there are important signals that it may be severe.

Southern Hemisphere Clues

Chief among these is the experience of the Southern Hemisphere. While not foolproof, the impact in the Southern Hemisphere can sometimes provide a rough indication of what the Northern Hemisphere can expect.

Of the 2 circulating influenza A strains, H1N1 and H3N2, it has been widely observed that seasons dominated by H3N2 are particularly deadly (especially to elderly people). This was the case this past season in Southern Hemisphere nations such as Australia, where confirmed flu cases were the highest they have been in 3 seasons.

Based on this experience, it is probable that the Northern Hemisphere will similarly be dominated by this deadlier strain of the virus.


Vaccine Changes

Southern and Northern Hemisphere influenza vaccines are developed at different times and sometimes are identical and sometimes different. For this season, the H3N2 portions of the vaccine were identical, and the Southern Hemisphere’s severe H3N2 season occurred in spite of the vaccine, which is another indication that a similar season might ensue in the north.

After the end of the Southern Hemisphere’s season, the selection process was undertaken for the 4 strains to include in the following season’s vaccine. The H3N2 component of the vaccine was updated.


Universal Flu Vaccine Need

The experience of the Southern Hemisphere should underscore the need for healthcare providers and facilities to be prepared for a more severe flu season and the medical care surge that will accompany it. Diagnostic testing algorithms, vaccination programs, antiviral medication treatment pathways, and infection control protocols should be reviewed, updated, and disseminated. That a severe season occurred in the Southern Hemisphere despite vaccinations, coupled with the fact that constant vigilance is required to constantly update vaccines, reinforces the need to develop a universal flu vaccine capable of providing robust protection season after season.



Branswell H. Flu experts see potential for a nasty flu season. STAT October 16, 2017. Accessed October 19, 2017.