Sunday, October 29, 2017

More Evidence Flu Shots May Improve Outcomes In Critical Patients


Going into this 2017-18 flu season there are signs that the H3N2 component of this year's flu vaccine (which is carried over from last year) - may be - in the words of the ECDC - `Suboptimal'
This is not exactly a shock, since last winter its Vaccine Effectiveness (VE) was less than stellar, and the WHO recently recommended a strain change for next year's Southern Hemisphere flu shot (see WHO: Recommended Composition of The 2018 Southern Hemisphere Flu Vaccine).
As we've discussed often (see The Enigmatic, Problematic H3N2 Influenza Virus), coming up with a good vaccine match for seasonal H3N2 has become increasingly difficult in recent years due largely to increased viral diversity, and mutations that can crop up during the (primarily egg-based) manufacturing process.

Last winter's jab provided only modest level of protection (34%) against H3N2, according to the CDC's MMWR report of June 30th.  More recently evidence has surfaced suggesting the vaccine's effectiveness may have declined even further over our summer, including:
Eurosurveillance: Low H3N2 Vaccine Effectiveness In Australia's 2017 Flu Season
Eurosurveillance: Low 2016/17 Vaccine Effectiveness (VE) Among Elderly Hospitalized H3N2 Cases

Australian CMO Statement On Flu Vaccine Effectiveness

While none of this is welcome news, and may portend (as we've already seen in Hong Kong and Australia this year) a severe upcoming flu season - there are still good reasons to get the flu shot this year.

The first is the flu jab contains 3 (or 4 if you get the quadrivalent shot) different flu strains: H3N2, H1N1, and 1 or 2 B strains.  It's effectiveness against influenza B has been pretty good - nearly 60% - while its protection against H1N1 has run about 50% (cite).
Influenza B, in particular, can be a serious threat in the spring, and while expected to be a minor player this winter, some H1N1 may be around as well. 
But perhaps the biggest reason is - even if this year's H3N2 component doesn't keep you from getting sick - there is growing evidence it can 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.

The CDC described the study:
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 . . . )

We've another study, scheduled to be presented today at the CHEST annual meeting in Toronto and published in the journal CHEST, that - while small - also suggests that vaccinated patients fare better than unvaccinated ones when hospitalized with influenza.

Follow the link to read the full abstract:

H1N1 Influenza (2015-2016): Critical Illness Outcomes in Vaccinated vs Unvaccinated Patients
Twinkle Chandak, Casey Joseph, Mridula Jacob, Gabriela Ciofoaia, Steven Lau
Berkshire Medical Center, Lenox, MA

Full Text
SESSION TITLE: Acute Lung Injury & Respiratory Failure

SESSION TYPE: Original Investigation Slide

PRESENTED ON: Sunday, October 29, 2017 at 01:30 PM - 03:00 PM

PURPOSE: Since the 2010-2011 influenza season, the trivalent influenza vaccine has included antigen from the 2009 pandemic H1N1 influenza A virus. This has prevented 700,000-1,500,000 cases of influenza A(H1N1), upto 10,000 hospitalizations, and 500 deaths based on surveillance data (2013). Very few studies in post-pandemic period exist, comparing clinical outcomes in vaccinated versus unvaccinated patients. Intuitively, we could imagine that unvaccinated patients would have higher severity of illness with poorer outcomes. So we conducted a retrospective analysis of patients hospitalized with influenza A(H1N1) during the influenza season of 2015-2016 and compared critical care outcomes in the two groups.
CONCLUSIONS: Although the study is limited by a small N value, we conclude that patients hospitalized with influenza A(H1N1) with prior vaccination had a lower risk of developing AKI when compared to vaccinated patients. Their respiratory failure was more likely to be managed with non-invasive ventilation thereby reducing the need of invasive MV. There was tendency toward lower risk of ICU admission, ARDS and organ dysfunction in vaccinated individuals.

CLINICAL IMPLICATIONS: Vaccinated patients with influenza A(H1N1) requiring hospitalization tend to have better outcomes than unvaccinated patients. The fact that significant proportion of unvaccinated patients are younger, emphasizes the need for widespread influenza vaccination. Larger studies are warranted to validate this data.
While not the USP (unique selling point) for the flu shot that most public health officials would wish for this fall, given the morbidity and mortality of severe influenza, even a modest reduction in severity can yield substantial benefits.
For some patients it can literally mean the difference between life and death, or between managing the flu at home or ending up in the hospital.
There is no question we need a better flu vaccine, and while we've seen some progress with high dose, adjuvanted, and quadrivalent vaccines, many of the deficits outlined in 2012's CIDRAP: The Need For `Game Changing’ Flu Vaccines remain. 
Right now, despite early reports, the jury is still out on just how much protection the flu shot will provide this winter. Much will depend upon which clade of H3N2 dominates your region.  Some areas will likely fare better than others.
For me, flu shots are all about risk reduction. I accept they aren't perfect, and some years they are far less effective than we'd like.
Much like wearing a seat belt - which don't prevent accidents, but can increase your odds of survival if you are in one - flu shots may help reduce the severity or duration of your illness and improve your chances of a good outcome.

While the benefits remain difficult to quantify, and likely vary widely between individuals, I'll take whatever advantage I can get.

Admittedly, we're not facing an ideal scenario - but getting the flu shot - along with practicing good flu hygiene (covering your coughs, washing your hands, staying home when you are sick, etc.) still remain the best steps you can take to stay healthy during what may turn out to be a particularly difficult flu season ahead.

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