In a large retrospective study from Australia, influenza vaccination during pregnancy lowered women's risk of acute respiratory infections (ARIs) requiring emergency room treatment or hospitalization by more than 60%, according to a report published May 20 in Vaccine.
And in other flu vaccine news, a study presented at a European meeting today suggests that the vaccine reduces the risk of hospitalization in patients who have heart failure.
Low vaccination rate in pregnant women
In the pregnancy study, the authors say previous research indicates that maternal flu vaccination can prevent hospitalization in young infants, but there is limited evidence for a protective effect of vaccination in pregnant women, who are at risk for severe illness if they contract flu.
The researchers examined the records of 34,701 women in Western Australia who gave birth from Apr 1, 2012, to Dec 31, 2013, to determine vaccination status and identify ARIs during the 2012 and 2013 flu seasons. They found that only 3,007 (8.7%) of the women received a seasonal flu shot during pregnancy.
The incidence of emergency department (ED) visits for ARIs in vaccinated women during the flu seasons was 9.7 visits per 10,000 person-days, versus 35.5 per 10,000 person-days for unvaccinated women. The authors calculated an adjusted hazard ratio of 0.19 (95% confidence interval [CI], 0.05 to 0.68) for the vaccinees, indicating an 81% lower risk.
The team found that the vaccinated women also had a lower rate of ARI-related hospitalizations: 16.2 versus 34.0 per 10,000 person-days. The adjusted hazard ratio was 0.35 (95% CI, 0.13 to 0.97), signaling a 65% lower risk.
The authors found that lab-confirmed flu hospitalizations were less common in the vaccinated women than the unvaccinated ones, but because of small numbers, the difference was not significant (hazard ratio, 0.16; 95% CI, 0.01 to 1.76).
The researchers say theirs appears to be the first population-based cohort study to show that seasonal flu vaccines help prevent hospital-attended respiratory illness in pregnant women.
Protection for heart failure patients
The study on heart failure patients was reported today at Heart Failure 2016 and the 3rd World Congress on Acute Heart Failure in Florence, Italy, according to a press release from the European Society of Cardiology (ESC).
To assess the impact of flu vaccination on hospitalization, researchers combed UK Department of Health medical records for 4.9 million patients over the period from 1990 to 2013. They compared the risk of hospitalization in a year when a patient was vaccinated and an "adjacent" year when he or she was not.
Analyzing data on 59,202 heart failure patients, the researchers found that vaccination was associated with a 30% lower risk of hospitalization for cardiovascular diseases, a 16% lower risk of hospitalization for respiratory infections, and a 4% lower risk of all-cause hospitalization in the period 31 to 300 days after vaccination, compared with the corresponding period in an adjacent vaccination-free year.
The risk reduction was greatest in the period 31 to 120 days after vaccination and in younger patients, meaning those under age 66, according to the release. There was no difference in risk reduction between men and women.
"The researchers validated the findings by looking at the association between vaccination and hospitalization due to cancer, an uncorrelated outcome," the release states. "As anticipated, there was no association, which supported the validity of the analysis."
See also:
May 20 Vaccine abstract
May 23 ESC press release
