Severity of influenza A and B infections similar in hospitalized children

Influenza A and B infections show comparable clinical severity in children, a study has shown.

“For optimal protection against severe influenza illnesses, the use of quadrivalent vaccines containing both lineages of B viruses seems warranted in children,” the researchers said.

An analysis was performed on the outcomes, management and clinical presentation of all children aged <16 years admitted to Turku University Hospital in Finland, with virologically confirmed influenza A or B infection during the 14-year period of 1 July 2004 to 30 June 2018.

The researchers carried out all comparisons between influenza A and B both within predefined age groups (0–2, 3–9 and 10–15 years) and in all age groups combined.

A total of 391 children were admitted to the hospital, of which 279 (71.4 percent) were diagnosed with influenza A and 112 (28.6 percent) with influenza B. Whether analysed by age group or among all children, no significant between-group differences were observed in any clinical features or outcomes, management, treatment at intensive care unit, or length of stay. [Pediatr Infect Dis J 2020;39:489-493]

Clinical suspicion of sepsis prompted the collection of blood cultures from 101 (36.2 percent) children with influenza A and 39 (34.8 percent) with influenza B (p=0.80). Blood cultures in three children with influenza A yielded a bacterial pathogen (one each of Streptococcus pneumoniae, S. pyogenes and Staphylococcus aureus).

Additionally, lumbar puncture was conducted in 16 (5.7 percent) children with influenza A and 11 (9.8 percent) with influenza B (p=0.15) to obtain cerebrospinal fluid specimens for suspected meningitis. None of the specimens screened positive for any bacteria.

“Our findings provide strong evidence against the conventional concept that influenza A viruses cause more severe illnesses than B viruses in children,” the researchers said.

Data from the National Infectious Diseases Register in Finland showed an average annual proportion of 72.3 percent for influenza A viruses and 27.7 percent for influenza B viruses among all influenza viruses detected in children aged <15 years in the catchment area during the 14-year period of this study. [https://thl.fi/en/web/infectious-diseases/surveillance]

“These frequencies are similar to our observed percentages of children hospitalized with A and B infections (71.4 percent and 28.6 percent), and the proportions of children hospitalized with A and B viruses during each individual season were very well in agreement with the proportions of A and B viruses detected in the child population,” the researchers said.

These findings also support the development of influenza immunization programmes for children, according to the researchers, noting that although the ultimate goal of vaccination is to prevent all influenza illnesses, prevention of the severe forms of the disease takes highest priority. [Lancet Child Adolesc Health 2018;2:338-349; N Engl J Med 2013;369:2481-2491; Eur J Clin Microbiol Infect Dis 2016;35:1107-1113]

“As influenza B accounts for a substantial proportion of all influenza illnesses and because the clinical severity of B infections is similar to influenza A, the use of quadrivalent influenza vaccines that contain both circulating lineages of B viruses seems warranted in children,” the researchers said.

Several studies from different countries that examined the cost-effectiveness of switching from trivalent to quadrivalent influenza vaccines support the above conclusion. [BMC Infect Dis 2015;15:465; Pharmacoeconomics 2016;34:939-951; Pharmacoeconomics 2016;34:1299-1308]