Effect of Repeated Vaccination With the Same Vaccine Component Against 2009 Pandemic Influenza A(H1N1) Virus

<span class="paragraphSection"><div class="boxTitle">Abstract</div><div class="boxTitle">Background.</div>The 2009 pandemic influenza A(H1N1) (A[H1N1]pdm09) vaccine component has remained unchanged from 2009. We estimate the effectiveness of current and prior inactivated influenza A(H1N1)pdm09 vaccination from influenza seasons 2010–2011 to 2015–2016.<div class="boxTitle">Methods.</div>Patients attended with influenza-like illness were tested for influenza. Four periods with continued A(H1N1)pdm09 circulation were included in a test-negative design.<div class="boxTitle">Results.</div>We enrolled 1278 cases and 2343 controls. As compared to individuals never vaccinated against influenza A(H1N1)pdm09, the highest effectiveness (66%; 95% confidence interval, 49%–78%) was observed in those vaccinated in the current season who had received 1–2 prior doses. The effectiveness was not statistically lower in individuals vaccinated in the current season only (52%) or in those without current vaccination and >2 prior doses (47%). However, the protection was lower in individuals vaccinated in the current season after >2 prior doses (38%; <span style="font-style:italic;">P</span> = .009) or those currently unvaccinated with 1–2 prior doses (10%; <span style="font-style:italic;">P</span> < .001). Current-season vaccination improved the effect in individuals with 1–2 prior doses and did not modify significantly the risk of influenza in individuals with >2 prior doses.<div class="boxTitle">Conclusion.</div>Current vaccination or several prior doses were needed for high protection. Despite the decreasing effect of repeated vaccination, current-season vaccination was not inferior to no current-season vaccination.</span>

from #AlexandrosSfakianakis via Alexandros G.Sfakianakis on Inoreader http://ift.tt/2qS72ZB
via IFTTT