Influenza Vaccine May Benefit Elderly Patients With Asthma

Despite a lack of significant protection against the flu in elderly patients with asthma, influenza vaccination may still confer benefits by reducing negative outcomes and mortality associated with contracting influenza, according to results of a case-controlled study from Spain reported in the Journal of Asthma.¹

Vaccinated patients with asthma who entered the hospital with a diagnosis of influenza were more likely to have had a longer duration of clinically milder symptoms and no short-term mortality associated with the flu.

Asthma is a frequent condition in both the elderly and hospitalized adults², and may be triggered or exacerbated by influenza infection. However, previous studies have been inconclusive about the benefits of the influenza vaccine in this population.³

In the current study, rates of influenza were not significantly reduced by vaccination, but there was a trend toward fewer symptoms and improved outcomes in patients who had been vaccinated compared with patients who had not. The severity of flu symptoms was milder in vaccinated patients compared with unvaccinated patients, who had a lower risk of being admitted to the intensive care unit (2.2% vs 15.2%, respectively), as well as a lesser need for invasive mechanical ventilation (4.3% vs 28.3%, respectively).

Mortality rates were also improved; no deaths were reported in vaccinated patients 30 days after discharge from the hospital, while 4.3% of unvaccinated patients died in the hospital and another 6.5% died within 30 days of discharge.

The case-matched study cohort of 2152 patients aged 65 years and older included 582 hospitalized patients with influenza (15.8% with asthma) and 1570 hospitalized patients without influenza (7.9% with asthma) recruited from 20 hospitals across 7 regions in Spain from November 2013 to May 2015.

As expected, vaccination significantly protected against influenza in patients without asthma (adjusted odds ratio (aOR), 0.63; 95% CI, 0.45-0.88), but also indicated a small protective effect in patients with asthma (aOR, 0.79; 95% CI, 0.34-1.81).

In univariate analysis, the same patterns were also observed: a significant protective effect on control patients without asthma (OR, 0.73; 95% CI, 0.59-0.91), with a small protective effect seen in patients with asthma who were vaccinated (OR, 2.02; 95% CI, 1.28-3.18) compared with patients with asthma who not vaccinated (OR, 2.06; 95% CI, 1.30-3.25).

The researchers noted an average vaccination rate of 50% of influenza patients in the study with asthma and 49% without asthma — the same global rate of vaccination in the elderly in the 2014 to 2015 influenza season. They reported a trend toward protection against influenza conferred by the vaccination in elderly patients with asthma, and in the absence of better evidence, recommended that, “the emphasis on vaccination of this group should continue.”

Study limitations included a potential influence on vaccination rates by excluding patients hospitalized with a respiratory infection, and challenges to antigen matching of the seasonal vaccine to the circulating virus, which was overcome by studying 2 seasons. The investigators also noted “a major problem defining asthma,” and suggested that the study may have been underpowered for detection of an effect of medium size.

References

1. Suárez-Varela MM, Llopis A, Fernandez-Fabrellas E, et al. Asthma and influenza vaccination in elderly hospitalized patients: Matched case-control study in Spain [published online June 21, 2017]. J Asthma. doi:10.1080/02770903.2017.1332204 
2. Fiore AE, Shay DK, Broder K, et al. Prevention and control of influenza: recommendations of the Advisory Committee on Immunization Practices (ACIP). Mortal Wkly Rep 2008;57;1-60.  www.cdc.gov/mmwr/preview/mmwrhtml/rr57e717a1.htm. Accessed August 2, 2017.
3. Cates CJ, Rowe BH. Vaccines for preventing influenza in people with asthma. Cochr Datab Syst Rev 2013;(2):CD000364. doi:10.1002/14651858.CD000364.pub4