ATLANTA – Individuals who neglect to get their annual influenza vaccinations will likely experience more-severe symptoms and a longer duration of the illness if they contract the disease, specifically the A/H3N2 strain.
In a study of 155 influenza patients between 2009 and 2014, 138 (89%) were positive for influenza A virus, 111 (72%) of whom were vaccinated against influenza.
“We know that flu vaccines are about 60% effective, but of that remaining 40%, do they still get severe flu? The data from our study say no,” explained Dr. Eugene V. Millar of the Uniformed Services University of the Health Sciences in Bethesda, Md.
Sixty-six (48%) individuals contracted the A/H3N2 strain of the influenza virus; of these patients, those who did not get vaccinated reported higher average severity scores for upper respiratory symptoms (7 vs. 3), lower respiratory symptoms (7 vs. 3), systemic symptoms (9.5 vs. 6), and total symptoms (22 vs. 12) than did subjects who did get vaccinated (P less than .01).
“People ask me all the time why I bother getting a flu vaccine if it never works,” Dr. Millar said. “I tell them that if you’re walking around and talking to people, then it did work, even if you feel a little lousy; if you didn’t get that vaccination, you’d be on your back.”
Such disparity in the severity and duration of symptoms was not noted in 69 (50%) of the 155 influenza patients who contracted the A/H1N1 strain of the virus, nor in the 3 (2%) subjects who had an “untyped” form of influenza A. However, Dr. Millar cautioned that results regarding H1N1 may have been confounded by a couple of factors.
“As we’ve seen with the [H1N1] pandemic, it was just a pandemic of the sniffles, so it’s very hard to assess symptom severity when the differences are moderate to none,” Dr. Millar explained, adding that the variant strain of H3N2 which became prevalent during the 2014-2015 respiratory season proved to be the far more severe disease. Furthermore, patients found with A/H1N1 were more likely to be put on antivirals, making it impossible to look at vaccine effect.
In total, 884 patients with influenza-like illness were screened for inclusion in the study, from which the sample of 155 subjects was eventually derived. Median age of the 155 subjects was 30.6 (P = .61), mean body mass index was 27.6 kg/m2 (P = .07), males outnumbered females 88 to 67, and 106 subjects were active-duty military at the time they had influenza.
“These are healthy people presenting to outpatient [clinics], it’s very interesting to see if the same thing would hold true for the elderly or people with underlying medical conditions, since those are the people we’re really trying to protect not only from influenza, but its complications, as well, such as secondary bacterial pneumonia.”
Nine subjects (6%) had influenza during the 2009-2010 season, 56 (36%) during the 2010-2011 season, 16 (10%) during the 2011-2012 season, 38 (25%) during the 2012-2013 season, and 36 (23%) during the 2013-2014 season.
This study was supported by the Infectious Disease Clinical Research Program (IDCRP), a Department of Defense program carried out via the Uniformed Services University of the Health Sciences, and the National Institute of Allergy and Infectious Diseases, a division of the National Institutes of Health. Dr. Millar did not report any relevant financial disclosures.