Markers of prognosis specific to influenza infection: are we there yet?

Influenza vaccine effectiveness among high-risk groups: A systematic literature review and meta-analysis of case-control and cohort studies

Vaccination represents the most effective intervention to prevent infection, hospitalization and mortality due to influenza. This meta-analysis quantifies data reporting influenza vaccine effectiveness (VE) on influenza visits and hospitalizations of case-control and cohort studies among high-risk groups.

A systematic literature review including original articles published between 2007 and 2016, using a protocol registered on Prospero with No. 42017054854, and a meta-analysis were conducted.

For 3 high-risk groups (subjects with underlying health conditions, pregnant women and health care workers) only a qualitative evaluation was performed. The VE quantitative analysis demonstrated a clear significant overall effect of 39% (95%CI: 32–46%) for visits and 57% (95%CI: 30–74%) for hospitalization among children. Considering the elderly influenza VE had a clear effect of 25% (95%CI: 6–40%) for visits and 14% (95%CI: 7–21%; p<0.001) for hospitalization.

This study showed the high VE of influenza vaccination among high-risk groups, representing a tool for public health decision-makers to develop evidence-based preventive interventions to avoid influenza outcomes.

Seasonal Influenza A H1N1pdm09 Virus and Severe Outcomes: A Reason for Broader Vaccination in Non-Elderly, At-Risk People

Background

Recent pandemics of influenza A H1N1pdm09 virus have caused severe illness, especially in young people. Very few studies on influenza A H1N1pdm09 in post-pandemic periods exist, and there is no information on the severity of both seasonal influenza A(H1N1) and A(H3N2) from the same season, adjusting for potential confounders, including vaccine.

Methods and Results

We performed a retrospective observational study of adults hospitalized during the 2014 season with influenza A(H1N1) or A(H3N2). All patients underwent the same diagnostic and therapeutic protocol in a single hospital, including early Oseltamivir therapy. We included 234 patients: 146 (62.4%) influenza A(H1N1) and 88 (37.6%) A(H3N2). A(H1N1) patients were younger (p<0.01), developed more pneumonia (p<0.01), respiratory complications (p = 0.015), ARDS (p = 0.047), and septic shock (p = 0.049), were more frequently admitted to the ICU (p = 0.022), required IMV (p = 0.049), and were less frequently vaccinated (p = 0.008). After adjusting for age, comorbidities, time from onset of illness, and vaccine status, influenza A(H1N1) (OR, 2.525), coinfection (OR, 2.821), and no vaccination (OR, 3.086) were independent risk factors for severe disease.

Conclusions

Hospitalized patients with influenza A(H1N1) were more than twice as likely to have severe influenza. They were younger and most had not received the vaccine. Our findings suggest that seasonal influenza A(H1N1) maintains some features of pandemic viruses, and recommend wider use of vaccination in younger adult high-risk patients.

Serum and mucosal antibodies fail as prognostic markers during critical influenza A infection

BACKGROUND

Previous studies have indicated that the absence of serum antibodies to influenza A H1N1 virus on day 4 after onset of symptoms predicted a fatal outcome in patients critically ill with influenza. The underlying mechanism was suggested to be the trapping of anti-influenza antibodies in pulmonary immune complexes.

OBJECTIVES

To study serum and mucosal antibodies as prognostic markers in patients with severe influenza A H1N1 infection.

STUDY DESIGN

Blood and respiratory samples (n=324) from 12 patients with severe influenza were analysed for anti-H1N1 antibodies with and without immune complex dissociation from symptom onset until convalescence or death (follow up 14-169 days). Eleven healthy subjects were analysed for comparison.

RESULTS

One of the 12 patients died from influenza pneumonia and had no detectable anti-H1N1 serum antibodies. However, also 2 of the 11 surviving patients remained negative for anti-H1N1 serum antibodies during follow-up (20 and 41 days, respectively). In six of the 11 survivors serum antibodies on day 4 were negative, but turned positive between day 7 and 23. In the remaining 3 patients antibodies were detected in the first 4 days of illness. Mucosal IgG or IgA was detected in all of the patients regardless of their clinical outcome and in 4 of 11 healthy subjects. No mucosal immune complexes were found in the patient who died but were detected in 3 of the 11 survivors.

CONCLUSIONS

This study suggests that no prognostic conclusions can be drawn from anti-H1N1 serum and mucosal antibodies in patients with severe influenza.