J Med Assoc Thai 2003; 86 (6):497

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Economic Evaluation of Influenza Vaccination in Thai Chronic Obstructive Pulmonary Disease Patients
Wongsurakiat P Mail, Lenakyamanee J , Maranetra KN , Jongriratanakul S , Sangkaew S

To determine the cost-effectiveness and cost-benefit of influenza vaccination in chronic
obstructive pulmonary disease (COPD) patients the authors conducted a stratified randomized, double-
blind, placebo-controlled trial from June 1997 to November 1998 at a university hospital in Thailand.
A total of 125 COPD patients were stratified based on their FEY1 as mild COPD (FEY1
70% pre-
dicted), moderate COPD (FEY 1 50-69% predicted) and severe COPD (FEY 1
50% predicted) and in
each severity stratum they were randomized to the vaccine group (received intramuscular injection with
purified trivalent split-virus vaccine containing A!fexas/36/91 (Hl N 1 ), A/Nanchang 1933/95 (H3N2)
and B/Harbin 107/94) or the placebo group (received intramuscular injection with vit B 1). Number of
episodes of acute respiratory illness (ARI) related to influenza (clinical ARI +a serum hemagglutina-
tion inhibition antibody titre of 38 or greater and a four fold titre increase in convalescent serum com-
pared to acute serum) as well as severity of each ARI (outpatient treatment, hospitalization or required
mechanical ventilation) and costs of treatment (direct medical costs comprised real drug costs from the
hospital dispensary in outpatient cases and real charges in hospitalization cases) were collected and
analyzed for the cost-effectiveness and cost-benefit of influenza vaccination.
The incidence of influenza-related ARI in the study year was 27 per cent in the placebo group
and 6.4 per cent in the vaccine group (relative risk [RR] 0.24, vaccine effectiveness 76%). The inci-
dence was 27.3 per cent, 23.5 per cent and 29.2 per cent in mild, moderate and severe COPD respec-
tively in the placebo group and 4.3 per cent, 12.5 per cent, and 4.3 per cent in the mild, moderate and
severe COPD respectively in the vaccine group (RR 0.16, 0.53 and 0.15; vaccine effectiveness 84%,
47%, and 85% respectively). The incremental cost-effectiveness ratios demonstrated that for every 100
patients with mild COPD whom the authors decided to vaccinate, the cost would be 24,840 baht more
and would prevent 18.2 outpatients, 4.8 hospitalizations and 0 patient from mechanical ventilation due
to ARI related to influenza. Likewise, the authors would have prevented 5.1 outpatients, 5.9 hospitali-
zations, 5.9 mechanical ventilation and 20.8 outpatients, 3.9 hospitalizations, 8.3 mechanical ventila-
tion for every 100 moderate COPD and every 100 severe COPD patients vaccinated respectively. More
than 90 per cent of the costs of treatment of influenza-related ARI were costs of hospitalization and
for patients with moderate and severe airflow obstruction, more than 90 per cent of these costs were
attributed to the costs of treating the patients who required mechanical ventilation. Predicted cost

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