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Influenza B associated with similar illness severity, ICU admission rate as influenza A

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February 11, 2019

Patients with influenza B had similar rates of associated disease severity and ICU admission compared with patients with influenza A(H1N1) during two recent influenza seasons in Jerusalem, researchers reported.

“The role of influenza B virus as a cause of severe disease and ICU admissions has been overcast for years by the magnitude of disease associated with influenza A viruses,” Maya Korem, MD, senior physician in the department of clinical microbiology and infectious diseases at Hadassah Hebrew University Medical Center, and colleagues wrote. “In recent years, influenza B has been increasingly recognized as a cause of hospitalization and mortality, especially among children, yet the number of comparative reports of the clinical severity of influenza A and B in adults is still limited.”

For their study, Korem and colleagues included all adult and pediatric patients with laboratory-confirmed influenza admitted to three major medical centers from November 2015 to April 2016, and from November 2017 to April 2018.

During the two seasons, 964 patients were diagnosed with influenza, and the majority of cases were influenza A(H1N1)pdm09 and influenza B. According to the study, 6.5% of all patients hospitalized with influenza were admitted to the ICU. Of those, 6.1% of patients hospitalized with influenza B were admitted to the ICU compared with 6.9% of patients hospitalized with H1N1.

The researchers reported observing higher rates of chronic lung disease exacerbation in patients with influenza B, whereas patients with H1N1 had higher rates of viral pneumonia and acute respiratory distress syndrome and lower white blood cell counts. Between the groups, however, no significant differences were observed for any of the measured parameters of illness severity, according to Korem and colleagues. They found that patients with influenza B had shorter stays in the ICU, although this was statistically significant only for the 2017-2018 season.

When the researchers reviewed vaccine type, they found that all patients had received the trivalent vaccine. During both influenza seasons, the vaccine was matched for influenza A strains and mismatched for the circulating influenza B lineages. According to the study, 63% of patients with influenza B were vaccinated compared with 25% patients with H1N1 (P = .01). Among ICU patients who were vaccinated, 73.9% had influenza B, and among nonvaccinated patients, 64.3% had H1N1.

Quadrivalent vaccines include one more influenza B virus than trivalent vaccines, providing broader immunity to influenza B, but are not currently “preferentially recommended” for adults, Korem and colleagues noted. According to the CDC, “No preference is expressed for any influenza vaccine over another.”

“Our findings highlight the potential ICU burden associated with influenza B, and call into question the equivalence of trivalent and quadrivalent vaccines in preventing severe influenza B,” Korem and colleagues wrote. – by Marley Ghizzone

Disclosures: The authors report no relevant financial disclosures.

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