It is no secret that for the elderly influenza can mean far more than just a few miserable days on the couch. Which is why, as I hurtle relentlessly towards that demographic, I get my flu shot every year, and encourage others to do the same.
But I do so with the knowledge that the effectiveness of the flu shot drops off significantly as the recipient grows older.
While there have been several new flu vaccine formulations released in recent years (see FLUAD & Fluzone) designed to boost the immune response in older patients, there is also the need to understand why regular flu vaccines fall short.
Seven years ago, in A Few Inflammatory Remarks, we looked at several studies that suggested that taking antipyretic medications – like acetaminophen, Aspirin, or other NSAIDs – could reduce the effectiveness of some vaccinations or blunt the level of acquired immunity from actual infection.
Last year's Study Suggests Low Dose Aspirin Doesn’t Reduce Flu Vaccine Immune Response, seems to exonerate LD aspirin – often taken daily to prevent heart attacks and strokes – but we cannot automatically assumed this to apply to other NSAIDs or antipyretics, or larger doses of aspirin.
Statins are another widely prescribed (40% of those > 65) class of prescription drug with proven anti-inflammatory and immunomodulatory effects, both of which could plausibly impact vaccine effectiveness.
Previously, and for the very same reasons, we’ve seen statins suggested as a possible treatment for pneumonia, pandemic influenza, and even MERS. While still the subject of study and debate, so far results from very limited real-world studies have been mixed.
Last fall, in JID: Statins & Flu Vaccine Effectiveness, we looked at two preliminary studies and a commentary on the possible effect of statins on flu vaccine effectiveness.
This past week the JID published a new study on the effect of statins on vaccine effectiveness (VE), which while subject to a number of limitations, produced some surprising results.
Primarily that the VE for influenza A/H1N1 and influenza B did not appear to be adversely affected by statin intake, but the VE for A/H3N2 was.
As H3N2 often produces more severe flu illness in the elderly, and more severe flu seasons in general, this is a potentially significant finding.
But exactly why the effect was only observed with H3N2 is a mystery.
The full (open access) study is available as a PDF, at the link below. When you return, I'll have a postscript:
J Infect Dis. 2016 Jul 28. pii: jiw335.
The Effect of Statin Use on Influenza Vaccine Effectiveness.
McLean HQ1, Chow BD1, VanWormer JJ1, King JP1, Belongia EA1.
Recent studies suggest that statin use may reduce influenza vaccine effectiveness (VE), but laboratory-confirmed influenza was not assessed.
Patients ≥45 years old presenting with acute respiratory illness were prospectively enrolled during the 2004-2005 through 2014-2015 influenza seasons. Vaccination and statin use were extracted from electronic records. Respiratory samples were tested for influenza.
The analysis included 3285 adults: 1217 (37%) statin nonusers, 903 (27%) unvaccinated statin nonusers, 847 (26%) vaccinated statin users, and 318 (10%) unvaccinated statin users. Statin use modified VE and influenza risk for A(H3N2) infection (p=0.002), but not for A(H1N1)pdm09 or B (p=0.2 and 0.4, respectively). VE against A(H3N2) was 45% (95% confidence interval [CI]: 27, 59) among statin nonusers and -21 (CI: -84, 20) among statin users. Vaccinated statin users had significant protection against A(H1N1)pdm09 (VE=68%, CI: 19, 87) and type B (VE=48%, CI: 1, 73). Statin use did not significantly modify VE when stratified by prior season vaccination. In validation analyses, the use of other cardiovascular medications did not modify influenza VE.
Statin use was associated with reduced VE against A(H3N2), but not A(H1N1)pdm09 or type B. Further research is needed to assess biologic plausibility and confirm these results.
© The Author 2016. Published by Oxford University Press for the Infectious Diseases Society of America.
Curiously, those taking statins but not vaccinated did see a noticeable protective effect (vs. unvaccinated and not taking statins) against influenza infection. The authors wrote:
Statin use alone (without vaccination) was associated with significantly reduced odds of A(H3N2) influenza when compared to unvaccinated nonusers. A similar effect of statin use alone was observed for A(H1N1)pdm09 and type B, but these were not statistically significant.
These results suggest that two potential statin effects should be evaluated in future studies: the potential interference of statins with vaccine-induced protection, and an independent protective effect from statin use that may reduce the risk of influenza in the unvaccinated population.
These findings may help pump new life into the idea - long promoted by Dr. David Fedson (retired Professor of Medicine at the University of Virginia School of Medicine and formerly Director of Medical Affairs, Aventis Pasteur MSD) - that statins might have a role in the treatment of pandemic influenza, particularly in resource limited regions of the world.
For more on this intriguing, but unproven theory, you may wish to revisit: