Saturday, May 27, 2017

CID Journal: Flu Vaccine Reduces Severe Outcomes in Hospitalized Patients


Although far from perfect, most years the seasonal flu vaccine provides a moderate level of protection against currently circulating influenza viruses. Much depends, however, on how close of a match the vaccine is to those viruses, and on the individual immune response of the recipient. 
Flu vaccines have provided reasonably good protection against H1N1 and Influenza B viruses in recent years  - often reaching  VE (Vaccine Effectiveness) Ratings 50%-60%.
The H3N2 vaccine component over the past few years has been problematic (see Eurosurveillance: Interim Estimates Of Flu Vaccine Effectiveness Against A(H3N2) - Canada, January 2017 and Branswell: H3N2 Remains the `Weak Link’ In The Flu Vaccine),  often providing only half that level of protection.

Although the elderly (> 65) are considered to be at greatest risk from influenza infection, they - by virtue of having a less robust immune system and more comorbidities - are also the group most apt to see reduced protection from the seasonal flu vaccine (see PLoS One: Limited Effectiveness Of Flu Vaccines In The Elderly & Flu Shots And The Elderly).
Which is not to say they don't derive benefits, just not as much as we'd like, considering their overall risks from influenza infection.

In 2011,  NFID - the National Foundation for Infectious Diseases - convened a group of experts to address the issues of influenza and the elderly. From that panel a 5-page brief  emerged, called: Understanding the Challenges and Opportunities in Protecting Older Adults from Influenza.

This report pointed out that although the elderly generally see less protection from the flu vaccine, older individuals may still mount a robust immune response. In populations 65 and older, the brief points out that:
  • Hospitalization rates for influenza and pneumonia are lower in community-dwelling adults who received the seasonal influenza vaccine.
  • Immunization is associated with reduced hospitalization of older patients for cardiac, respiratory, and cerebrovascular diseases.
While the goal of vaccinating the younger population is to prevent infection, the authors point out that:
  • . . . the goal in older adults is to prevent severe illness, including exacerbation of underlying conditions, hospitalization, and mortality. 
Since then, we've seen a good deal of research suggesting that even a little protection can mean a lot, particularly for those with elevated risk factors, like the elderly. In 2014, a study from the CDC: Flu Shots Reduce Hospitalizations In The Elderly, appeared to support those goals.

This past week, a new study in the journal Clinical Infectious Diseases suggests that even among those hospitalized with influenza, having been vaccinated is associated with less severe illness, lower mortality, and shorter hospitalization stays.

Influenza vaccination modifies disease severity among community-dwelling adults hospitalized with influenza
Carmen Sofia Arriola, DVM, PhD, Shikha Garg, MD , Evan J Anderson, MD , Patricia A Ryan, MS , Andrea George, MPH , Shelley M Zansky, PhD , Nancy Bennett, MD, MS , Arthur Reingold, MD , Marisa Bargsten, MPH , Lisa Miller, MD, MSPH

Clin Infect Dis cix468.
Published: 19 May 2017


We investigated the effect of influenza vaccination on disease severity in adults hospitalized with laboratory-confirmed influenza during 2013−14, a season in which vaccine viruses were antigenically similar to those circulating.

We analyzed data from the 2013−14 influenza season, and used propensity score matching to account for the probability of vaccination within age strata (18−49, 50−64 and ≥65 years). Death, intensive care unit (ICU) admission, and hospital and ICU lengths of stay (LOS) were outcome measures for severity. Multivariable logistic regression and competing risk models were used to compare disease severity between vaccinated and unvaccinated patients, adjusting for timing of antiviral treatment and time from illness onset to hospitalization.

Influenza vaccination was associated with a reduction in the odds of in-hospital death among patients aged 18−49 years (adjusted odds ratios [aOR] =0.21; 95% confidence interval [CI], 0.05 to 0.97), 50–64 years (aOR=0.48; 95% CI, 0.24 to 0.97), and ≥65 years (aOR=0.39; 95% CI, 0.17 to 0.66). Vaccination also reduced ICU admission among patients aged 18−49 years (aOR=0.63; 95% CI, 0.42 to 0.93) and ≥65 years (aOR=0.63; 95% CI, 0.48 to 0.81), and shortened ICU LOS among those 50−64 years (adjusted relative hazards [aRH]=1.36; 95% CI, 1.06 to 1.74) and ≥65 years (aRH=1.34; 95% CI, 1.06 to 1.73), and hospital LOS among 50−64 years (aRH=1.13; 95% CI, 1.02 to 1.26) and ≥65 years (aRH=1.24; 95% CI, 1.13 to 1.37).

Influenza vaccination during 2013−14 influenza season attenuated adverse outcome among adults that were hospitalized with laboratory-confirmed influenza.
  The CDC published a summary of these results yesterday:

 New CDC Study Shows Flu Vaccine Reduces Severe Outcomes in Hospitalized Patients

 May 25, 2017 – A new study in the journal Clinical Infectious Diseases (CID) showed that flu vaccination reduced deaths, intensive care unit (ICU) admissions, ICU length of stay, and overall duration of hospitalization among hospitalized flu patients. This study is an important first step in better understanding whether flu vaccines can reduce severe flu outcomes even if they fail to protect against infection.

The study looked at hospitalized flu patients during 2013-2014 and compared patients who had been vaccinated to those who had not. The observed benefits were greatest among people 65 years of age and older, which is notable because people in this age group are at increased risk of serious flu complications and have the highest hospitalization rate among all age groups.

The study found that vaccinated adults were 52-79% less likely to die than unvaccinated flu-hospitalized patients. In other words, an unvaccinated hospitalized flu patient was 2 to 5 times more likely to die than someone who had been vaccinated.
(Continue . . . )

While influenza is hardly a trivial illness, for those of us over a certain (ahem) age, influenza increasingly becomes a threat to life. Just 10 days ago, in Int. Med. J.: Triggering Of Acute M.I. By Respiratory Infection, we saw additional evidence that a variety of respiratory infections - including influenza - can trigger heart attacks in the elderly.

While it doesn't protect against all respiratory infections - two years ago, in UNSW: Flu Vaccine Provides Significant Protection Against Heart Attacks, we saw a study that found that if you are over 50 - getting the flu vaccine can cut your risk of a heart attack by up to 45%
Which is one of the big reasons why I elect to get the vaccine every year (see  #NatlPrep: Giving Preparedness A Shot In The Arm).

While no drug or vaccine can claim to be 100% safe or benign, flu vaccines are among the safest drugs available - and given the mounting evidence influenza's toll - the rewards for me far exceed the risks.

Hopefully - after considering the pros and cons - they will for you, too.

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