Monday, January 08, 2018

CMAJ Research: Repeated Flu Vaccinations Reduce Severity of Illness In Elderly


With all of the talk about the poor performance of this year's H3N2 component of the Northern Hemisphere's flu vaccine (see ECDC: H3N2 Flu Vaccine Component Likely `Suboptimal'), I'm happy to have a little good news to report this morning.
A new study, published today in the CMAJ, finds that repeated yearly flu vaccinations reduce the severity of illness in the elderly - usually the hardest hit segment of the population - even when it fails to prevent infection. 
While the primary gauge of any vaccine's success is how well it prevents disease, with the flu vaccine - even in a good year - we only expect about a 60% -70% success rate. And that number drops significantly as recipients grow older (see Flu Shots And The Elderly).

While a more protective flu vaccine is sorely needed, in recent years we've seen growing evidence suggesting that even when the flu vaccine doesn't prevent infection - it may help reduce the severity of your illness.
This is an idea that has long been discussed (see 2011's NFID: The Challenges Of Influenza In Older Adults), but only recently have we begun seen some studies to back it up.  
In 2015, the ASM published Influenza vaccine, while not 100% effective, may reduce the severity of flu symptoms, which suggested: 
. . . that annual receipt of influenza vaccine, while not 100% effective in preventing disease, may be of some benefit by lessening the severity of symptoms among those who do get influenza. This study was conducted among young, otherwise healthy active duty military personnel and beneficiaries, and it is not known whether these findings would be consistent among individuals who are known to be at high-risk for complications due to influenza infection (e.g. pregnant women, elderly persons, and persons with underlying medical conditions).
More on point, last May in CID Journal: Flu Vaccine Reduces Severe Outcomes in Hospitalized Patients, we saw a study that suggested that among those hospitalized with influenza, having been vaccinated is associated with less severe illness, lower mortality, and shorter hospitalization stays.
Admittedly not ideal, but for thousands of flu victims every year this can mean the difference between life and death, or between managing the flu at home or ending up in the hospital.
The following study, conducted by Spanish researchers, looks at the effect of repeated flu vaccinations (current year, and up to past 3 seasons) on reducing severe flu illness among elderly patients who were admitted to 20 Spanish hospitals during the 2013-14 and 2015-16 flu seasons.

While vaccination in the current year did not show any statistically significant reduction in the severity of illness, repeated vaccinations over two or more years cut that rate in half.

Some excerpts from a much longer study follow:
Repeated influenza vaccination for preventing severe and fatal influenza infection in older adults: a multicentre case–control study 
Itziar Casado, Ángela Domínguez, Diana Toledo, Judith Chamorro, Jenaro Astray, Mikel Egurrola, María Amelia Fernández-Sierra, Vicente Martín, María Morales-Suárez-Varela, Pere Godoy and Jesús Castilla; for the Project PI12/02079 Working Group 

CMAJ January 08, 2018 190 (1) E3-E12; DOI:
BACKGROUND: The effectiveness of repeated vaccination for influenza to prevent severe cases remains unclear. We evaluated the effectiveness of influenza vaccination on preventing admissions to hospital for influenza and reducing disease severity.

METHODS: We conducted a case–control study in 20 hospitals in Spain during the 2013/14 and 2014/15 influenza seasons. Community-dwelling adults aged 65 years or older who were admitted to hospital for laboratory-confirmed influenza were matched with inpatient controls by sex, age, hospital and admission date.
The effectiveness of vaccination in the current and 3 previous seasons in preventing influenza was estimated for inpatients with nonsevere influenza and for those with severe influenza who were admitted to intensive care units (ICUs) or who died.
RESULTS: We enrolled 130 inpatients with severe and 598 with nonsevere influenza who were matched to 333 and 1493 controls, respectively. Compared with patients who were unvaccinated in the current and 3 previous seasons, adjusted effectiveness of influenza vaccination in the current and any previous season was 31% (95% confidence interval [CI] 13%–46%) in preventing admission to hospital for nonsevere influenza, 74% (95% CI 42%–88%) in preventing admissions to ICU and 70% (95% CI 34%–87%) in preventing death.
Vaccination in the current season only had no significant effect on cases of severe influenza. Among inpatients with influenza, vaccination in the current and any previous season reduced the risk of severe outcomes (adjusted odds ratio 0.45, 95% CI 0.26–0.76).
INTERPRETATION: Among older adults, repeated vaccination for influenza was twice as effective in preventing severe influenza compared with nonsevere influenza in patients who were admitted to hospital, which is attributable to the combination of the number of admissions to hospital for influenza that were prevented and reduced disease severity. These results reinforce recommendations for annual vaccination for influenza in older adults.

Effectiveness of vaccination for influenza on reducing severity

In patients admitted to hospital for influenza, vaccination in the current and any of the 3 previous seasons was associated with 55% lower odds of severity of disease (adjusted OR 0.45, 95% CI 0.26 to 0.76), 65% of admission to the ICU (adjusted OR 0.35, 95% CI 0.17 to 0.70) and 56% of death (adjusted OR 0.44, 95% CI 0.23 to 0.86).
However, vaccination in the current season only showed no reduced odds of severe disease and increased odds of death (adjusted OR 3.35, 95% CI 1.06 to 10.58) (Table 2), which is consistent with a preventive effect against nonsevere influenza but not against severe influenza.
(Continue . . . . )

Having received the flu vaccine every year now since 2004, I've been a bit concerned over recent reports (see CIDRAP's Studies shed light on effects of serial flu shots, current vaccine's benefits) suggesting serial receipt of the flu vaccine may sometimes reduce its effectiveness. 
These reports have not been persuasive enough to convince me to alter my flu shot regimen - but as I hurl headlong ever closer to my 65th birthday - this study offers a bit of reassurance that I'm following a prudent course.
While this is a multi-center case-control study conducted over two flu seasons, it is not without its limitations, and so additional studies will be needed to validate their results.

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