Over a period of 6 influenza virus seasons, the seasonal flu vaccine provided meaningful protection for asthma patients, according to the results of a study published in Clinical Infectious Diseases
Investigators from the University of Edinburgh examined patient data from 223 primary care practices in Scotland in order to estimate the effectiveness of the flu vaccine in adults and children with asthma. The patients, including children older than 6 months of age, were seen from the 2010-11 flu season to the 2015-16 season.
The study authors explained that having the flu is a trigger for asthma attacks, but uptick of flu vaccines in asthma patients often remains low. They thought concerns about vaccine effectiveness may be behind this low vaccination rate.
Throughout the study, the investigators collected 5910 swab samples from 5022 patients with asthma over the 6 flu seasons. Cases of the flu were confirmed using a polymerase chain reaction test and patients were subsequently categorized as cases (positive) or controls (negative). There were 781 positive swabs (13.2%) while the remaining swabs (86.8%) were negative for influenza.
Patients likely to test positive for the flu were aged between 45-64 years, lived in remote small towns, had no previous seasonal flu vaccine, and had a swab taken from a primary care facility, the study authors reported.
The study authors demonstrated the vaccine effectiveness in each season for asthma patients:
- 2010-11: 76.1% overall effectiveness
- Predominating subtypes: A/H1N1 (70.7% effective) and B (83.2%)
- 2011-12: 45.1% overall effectiveness
- Predominating subtype: A/H3N2
- 2012-13: 45.2% overall effectiveness
- Predominating subtypes: all influenza A subtypes, where H1N1 reached 77.5%, but lower effectiveness was observed in H3 and B strains.
- 2013-14: 52.3% overall effectiveness
- Predominating subtypes: A/H1N1
- 2014-15: 48.6% overall effectiveness
- Predominating subtypes: H3/N2 and B (which reached 77.0% effectiveness)
- 2015-16: 57.8% overall effectiveness
- Predominating subtypes: A/H1N1 and B (54.7% effectiveness)
The investigators determined that the influenza vaccination was linked to an overall 55% reduction in the risk of confirmed flu cases for patients with asthma, regardless of strain or subtype. Protection was better during seasons with good antigenic matches against the H1N1 and B influenza strains, which is why the investigators noted such a high rate of vaccine effectiveness in the 2010-11 season.
Vaccine effectiveness against influenza A was low in those aged 55 years and older, but vaccines were effective against influenza B. In patients under 18 years of age, influenza A vaccine effectiveness reached as high as 90.5, the study authors noted.
Because they tracked effectiveness across 6 flu seasons, the study authors wrote that they believe their findings can be generalized for the wider asthma population in Scotland. On the other hand, by only measuring prevention of influenza, and not the wider effects such as less severe asthma or subsequent lower risk of a more severe asthma attack, they cannot quantify total vaccination benefits from just this study on its own, they wrote.
“This study showed that vaccination can prevent influenza in individuals with asthma presented with influenza-like illness in Scottish primary and secondary care settings,” the study authors wrote. “While substantial variation in vaccine effectiveness was observed among circulating strains and age groups, protection was still observed in most subgroups… The findings of this study can guide research and policymakers for the provision of a more targeted and effective vaccination program improving the current protection of the asthma population.”
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