#17,082
While I get the flu vaccine every year, I am aware that there are some studies suggesting that with repeated flu vaccinations, comes the risk of mounting a diminished immune response.
In 2015, this idea made news around the globe (see Helen Branswell's report Getting a flu shot every year? More may not be better), following a preliminary report from Wisconsin’s Marshfield Clinic Research Foundation on the effectiveness of repeated flu vaccination in kids.A similar report appeared earlier in the CMAJ (see Repeated flu shots may blunt effectiveness).
But in 2018, the Marshfield Clinic released a followup report (below) which supports the receipt of the flu vaccine every year.
Friday, October 26, 2018
A Marshfield Clinic Research Institute study recently found that getting a flu vaccination one year did not reduce vaccine effectiveness the next year in children, findings that support current recommendations for children to be vaccinated annually against influenza.
The study was conducted by Huong McLean, Ph.D., and Edward Belongia, M.D., of the Center for Clinical Epidemiology and Population Health at Marshfield Clinic Research Institute, and was published in JAMA Network Open.
Also in 2018, in CMAJ Research: Repeated Flu Vaccinations Reduce Severity of Illness In Elderly, we looked at a study that found that repeated vaccinations over two or more years cut the rate of severe influenza illness in half.
Additionally, in 2019, a systematic review of the literature lent additional support to the idea of getting the flu vaccine every year, despite some decline in VE among people receiving back-to-back yearly flu vaccinations.
The impact of repeated vaccination on influenza vaccine effectiveness: a systematic review and meta-analysis
BMC Medicine volume 17, Article number: 9 (2019) Cite this article
Abstract
Background
Conflicting results regarding the impact of repeated vaccination on influenza vaccine effectiveness (VE) may cause confusion regarding the benefits of receiving the current season’s vaccine.
Conclusions
Our results support current season vaccination regardless of prior season vaccination because VE for vaccination in the current season only is higher compared to no vaccination in either season for all types/subtypes, and for H1N1 and influenza B, vaccination in both seasons provides better VE than vaccination in the prior season only. Although VE was lower against H3N2 and B for individuals vaccinated in both seasons compared to those vaccinated in the current season only, it should be noted that past vaccination history cannot be altered and this comparison disregards susceptibility to influenza during the prior season among those vaccinated in the current season only. In addition, our results for H3N2 were particularly influenced by the 2014–2015 influenza season and the impact of repeated vaccination for all types/subtypes may vary from season to season. It is important that future VE studies include vaccination history over multiple seasons to evaluate repeated vaccination in more detail.
The data is admittedly complex, and subject to interpretation, but my lack of flu-like illness (other than a single bout of COVID) over the past decade has made me a believer.
Repeated influenza vaccination induces similar immune protection as first-time vaccination but with differing immune responses
Beiwei Ye,Liumei Shu,Yuanyuan Pang,Yaxin Guo,Yuanyuan Guo,Kexin Zong,Cong Chen,Xianzhi Zheng,Jie Zhang,Maoshun Liu,Xiaoju Yuan,Yingze Zhao,Danni Zhang … See all authors
First published: 21 October 2022
Beiwei Ye, Liumei Shu, Yuanyuan Pang, and Yaxin Guo contributed equally to this work.
Abstract
Background
Recent seasonal epidemics of influenza have been caused by human influenza A viruses of the H1N1 and H3N2 subtypes and influenza B viruses. Annual vaccination is recommended to prevent infection; however, how annual influenza vaccination influences vaccine effectiveness is largely unknown.
Methods
To investigate the impact of repeated vaccination on immune and protective effect, we performed a prospective seroepidemiologic study. Participants with or without prior vaccination (2018–2019) were enrolled during the 2019–2020 influenza season. Inactivated quadrivalent influenza vaccine (IIV4) was administered through the intramuscular route, and venous blood samples were collected regularly to test hemagglutination inhibition (HAI) titers.
Results
The geometric mean titers and proportion with titers ≥40 against the influenza vaccine components peaked at 30 days post-vaccination. At Day 30, the geometric mean titer and proportion with titers ≥40 in participants who had been previously vaccinated were higher for H3N2 but similar for both B lineages (Victoria and Yamagata) as compared with participants vaccinated for the first time. As for H1N1, the geometric mean titer was lower in repeated vaccinated participants, but the proportion with titers ≥40 was consistent in both groups.
Conclusions
Repeated vaccination provides similar or enhanced protection as compared with single vaccination in first-time vaccinees.
(SNIP)
Overall, our study suggests that vaccination provides immune protection regardless of prior vaccination history. Consecutive influenza vaccinations can be effective in replenishing antibody levels and may be beneficial for the effectiveness of vaccination for the next season.
This result provides evidence to support decision-making for receiving the influenza vaccine annually. Based on the persistence of poor influenza vaccination rates in China,25 community health institutions should strengthen vaccine advocacy to increase immunization coverage. For vulnerable populations, community health care centers can establish health records and proactively remind individuals each year to receive their influenza vaccination ahead of the flu season.
While there is no doubt we need better seasonal flu vaccines, and that most years the flu shot only provides moderate levels of protection, even a little protection can make the difference between a few miserable days in bed and admission to the ICU.
