Monday, August 05, 2019

Study Suggests Flu Vaccine May Lower Stroke Risk in Elderly ICU Patients
From NFID Report


We've seen some pretty good evidence over the past several years that influenza (and other serious respiratory infections) can cause far more than just respiratory illness; they can sometimes lead to heart attacks and strokes in the weeks that follow.

A few examples include:
Eur. Resp.J.: Influenza & Pneumonia Infections Increase Risk Of Heart Attack and Stroke
NEJM: Acute Myocardial Infarction After Laboratory-Confirmed Influenza Infection
Int. Med. J.: Triggering Of Acute M.I. By Respiratory Infection

It stands to reason, that if you can reduce the incidence (or at least the severity) of influenza infection in the general population using the flu vaccine, you ought to be able to reduce the number of deaths among high risk individuals.
But the rub has been that the flu vaccine tends to work best in healthy, younger adults. 
Among those over 65, the flu vaccine is only moderately effective in preventing infection during a `good' year - and some years, and particularly against H3N2 -  vaccine effectiveness can be practically nil (see MMWR Interim Estimates of 2017–18 Seasonal Influenza Vaccine Effectiveness — United States, February 2018).

Despite these shortcomings, there's evidence to suggest that even when the vaccine doesn't prevent infection, it can reduce the severity of one's illness and thereby reduce morbidity and mortality.
To this growing list, we can add a new, population based study out of Denmark that suggests that receipt of the flu vaccine may reduce the risk of early death or stroke among elderly intensive care patients.

The study, published in Intensive Care Medicine (see link and abstract below), is, alas, behind a paywall. But we've an informative press release describing the study from Aarhus University.

Intensive Care Medicine

July 2019, Volume 45, Issue 7, pp 957–967 | Cite as

Influenza vaccination and 1-year risk of myocardial infarction, stroke, heart failure, pneumonia, and mortality among intensive care unit survivors aged 65 years or older: a nationwide population-based cohort study



We examined whether influenza vaccination affects 1-year risk of myocardial infarction, stroke, heart failure, pneumonia, and death among intensive care unit (ICU) survivors aged ≥ 65 years.

Compared with the unvaccinated ICU survivors, the influenza vaccinated ICU survivors had a lower 1-year risk of stroke and a lower 1-year risk of death, whereas no substantial association was observed for the risk of hospitalization for myocardial infarction, heart failure, or pneumonia. Our findings support influenza vaccination of individuals aged ≥ 65 years.
        (Continue . . . )

You'll find some extended excerpts from the press release from Aarhus University below, after which I'll return with a postscript.
Elderly intensive care patients who have been vaccinated against influenza have a reduced risk of dying and suffering strokes

Elderly critically ill patients who have been vaccinated against influenza have a reduced risk of dying and of suffering a blood clot or bleeding in the brain. This is shown by a study from Aarhus University and Aarhus University Hospital. The results support the WHO’s recommendation of influenza vaccinations for elderly people.

2019.07.29 | Mette Louise Ohana

It appears that an influenza vaccine does not just work when it comes to influenza. A new study shows that elderly people who have been admitted to an intensive care units have less risk of dying and of suffering a blood clot or bleeding in the brain if they have been vaccinated. And this is despite the fact that they are typically older, have more chronic diseases and take more medicine then those who have not been vaccinated.
Less than forty per cent of the elderly are vaccinated

The study covers almost 90,000 surviving intensive care patients above the age of 65 during an eleven year period in Denmark. Only a few of them were admitted directly due to influenza. However, regardless of the cause of the admission, for those who were vaccinated the risk of suffering a stroke – which is the collective name for bleeding and blood clots in the brain – was 16 per cent lower. This group also has an eight per cent lower risk of dying during the first year following their hospitalisation.


"We can't say with one hundred per cent certainty that the risk of a stroke and dying is lower solely because of the vaccine. But we can see that the elderly people who have been vaccinated do better in the event of critical illness. This suggests that it would be good if more elderly people received the vaccine. Not least because the vaccine is both safe and inexpensive,” says Christian Fynbo Christiansen.
The risk of pneumonia is not reduced

This is the first time that researchers have looked into the effect of the vaccine specifically on elderly critically ill patients. Other researchers have previously shown that the influenza vaccine lessens the risk of bacterial infections and heart attacks. However, the study shows that this is not the case for the elderly intensive care patients.

"Surprisingly, the vaccine didn’t reduce the number of pneumonia cases in our study. We had otherwise expect that it would, as some previous studies have shown that the vaccine has this effect on younger and healthy individuals.

Neither was there any clear difference in the number of blood clots in the heart. This raises new research questions about what effect of the vaccine on the immune system and whether there were other differences between the patients," says Christian Fynbo Christiansen.
The research results – more information
  • The study is a register-based cohort study that covers 89,818 patients who have survived hospitalisation in intensive care departments in Denmark during the period 2005-2015. Patients have been identified in the Danish Intensive Database along with associated information from other health registers.
  • The study was carried out with support from the Independent Research Fund Denmark and PROCRIN (the Program for Clinical Research Infrastructure) which has been established by the Lundbeck Foundation and the Novo Nordisk Foundation.

Clinical Associate Professor, PhD, Consultant Christian Fynbo Christiansen

Aarhus University Hospital and Aarhus University, Department of Clinical Medicine, Department of Clinical Epidemiology

Direct tel.: (+45) 8716 8218

Mobile: (+45) 2020 8398

Despite the encouraging findings, this study isn't exactly a slam dunk.  
Researchers haven't figured out a plausible mechanism by which the flu vaccine reduces strokes and/or early death in these patients, and there may be some confounders not taken into account. 
Still, when taken along with the other studies we've seen that also suggest some extended protection from the flu vaccine, it makes the seasonal flu vaccine - at least in my mind - worth getting every year. 
Even in those years when it only provides a moderate level of immunity against circulating flu strains.
Getting a yearly flu shot is like wearing a seat belt in an automobile.  It doesn't guarantee a good outcome in a wreck, but it does increase your odds of walking away. And despite the anti-vaccine rhetoric on the internet, flu vaccines have an excellent (albeit, not perfect) safety record.
Which is why I'll be rolling up my sleeve for the 15th year in a row. 
While no shortage in vaccines is currently expected, they will probably be a little late this year (see More Signs Of Delayed Delivery Of 2019-20 Flu Vaccine). Since it takes at least 2 weeks for you to build antibodies after getting the shot, my plan is to get mine as soon as they become available.

Hopefully you'll weigh the advantages, and elect to do the same.