Influenza Vaccine Effectiveness Bounces Back

Recent reports from the CDC have suggested that the flu vaccine is upwards of 47% effective this year, almost twice as much as last year. Despite elevated influenza activity, it appears that the vaccine is working better than the one created for the severe 2017-2018 flu season. The CDC’s surveillance team specializing in the Influenza virus has suggested that this year isolates from patients identify the most virulent strains in the United States consisted of A(H1N1)pdm09 and A(H3N2). The predominant A(H1N1)pdm09 was especially virulent in children, while the A(H3N2) strain was notably found in the southeastern continental United States. Overall, incidence of infection of many Influenza B viruses is less than 5%, with batches of tested samples positive for influenza ranging from 1.7% to almost 22% in any given week of the season. This variability can be attributed to the sigmoidal behavior of infection, consistent with past seasons, where infection is low in October and November, rises in late December, and peaks during February. This year infections were generally of lower severity, yet it was concluded that the proportion of individuals aged 5-24 years infected is on the rise. This proportion may stem from a few different potential causes: epidemiologically sensitive populations are getting infected less often, viral strains present in recent years are more infectious (as there are significantly more people aged 5-24 than 0-4 or 65+) across the entire population, or even that these younger populations are more likely to have access to healthcare and get tested for the flu.

This increase in effectiveness as compared to previous years is not only a good thing for those who are (and are not) vaccinated this year, but predicts hopeful trends for further prevention of influenza infection. This magnitude of increase is impressive, as the number of influenza vaccines is speculated to have decreased this year based on the perceived ineffectiveness of the vaccine last year (~25% effective). Despite this fact, it is estimated that the 2017-2018 vaccine prevented 7.1 million infections and over 8000 associated deaths.  The uphill battle against influenza infection is an ongoing issue and the CDC maintains strong surveillance of these infections in order to predict future infection patterns and prevent widespread disease when possible.

~Kyle Enriquez

Sources:

https://consumer.healthday.com/infectious-disease-information-21/flu-news-314/flu-shot-much-more-effective-this-year-cdc-says-742770.html

https://www.cdc.gov/mmwr/volumes/68/wr/mm6806a1.htm?s_cid=mm6806a1_w

https://www.cdc.gov/flu/weekly/