TORONTO – Patients who received an influenza vaccination but still required hospitalization for H1N1 influenza had better outcomes, compared with unvaccinated patients, according to findings from a retrospective study.
In the hospital, vaccinated patients had significantly lower rates of acute kidney injury (6% vs. 35%; P = .038) and were more likely to be satisfactorily managed with noninvasive mechanical ventilation (41% vs. 6%; P = .004).
Dr. Chandak and her colleagues studied 72 cases of seasonal influenza requiring hospitalization from September 2015 to April 2016 at Berkshire Medical Center, a 300-bed teaching hospital in western Massachusetts. Based on rapid polymerase chain reaction testing, 51 of these patients were positive for H1N1, of which 38 had received a seasonal flu vaccine.
H1N1 patients who had received vaccination were significantly older (70.4 years vs. 59.6 years; P = .016) and were more often smokers (76% vs. 38%; P = .017), compared with patients who were unvaccinated.
The finding that the unvaccinated patients were younger and still had poorer outcomes, “emphasizes the need for widespread vaccination,” Dr. Chandak said.
There were several parameters that trended in favor of vaccination, but did not reach statistical significance due to the relatively small sample size, Dr. Chandak said. These included a trend towards more ICU admission in the unvaccinated, compared with vaccinated patients (21% and 12%, respectively; P = .699), a longer ICU stay (1.7 days and 0.2 days; P = .144), more multiorgan dysfunction syndrome (12% and 6%; P = .654), and more acute respiratory distress syndrome (6% and 0%; P = .547). Vasopressors were needed in a similar proportion of patients (12% of both groups).
During the 2009-2010 flu season, H1N1 was the cause of about 61 million cases of influenza in the United States, 274,000 hospitalizations, and 12,470 deaths, Dr. Chandak reported.
Since the 2010-2011 influenza season, the trivalent influenza vaccine has included antigen from the 2009 pandemic H1N1 influenza A virus. This has prevented between 700,000 and 1.5 million cases of H1N1, up to 10,000 hospitalizations, and as many as 500 deaths, according to surveillance data ().
The viral subtype made a strong reappearance in the 2015-2016 flu season when it was again the predominant viral subtype of the season, according to the CDC. Most studies have looked at the effectiveness of the vaccine, but have not studied critical care outcomes in vaccinated versus unvaccinated patients, Dr. Chandak noted.
Dr. Chandak reported having no financial disclosures.