Surveillance épidémiologique de la grippe A(H1N1) 2009 dans les armées françaises : adaptation des systèmes de surveillance au contexte pandémique

Increase in reported adverse events following seasonal influenza vaccination among the French armed forces, 2008-2009: possible role of stimulated reporting and background cases of influenza-like infection

OBJECTIVES

In September 2009, an increase in seasonal influenza vaccine adverse events (VAE), compared with reports for previous years, was detected among the French armed forces in the setting of an extended immunization campaign. This work presents the results of this investigation.

STUDY DESIGN

VAE were surveyed among all French military personnel from 2008 to 2009 by Epidemiological Departments of the French Military Health Service. For each case, a notification form was completed, providing patient and clinical information.

METHODS

Case definitions were derived from the French drug vigilance guidelines. Three types of VAE were considered: non-serious, serious and unexpected. Incidence rates were calculated by relating VAE to the number of vaccine doses injected.

RESULTS

Forty-seven seasonal influenza VAE were reported in continental France: 18 in 2008 and 29 in 2009. The annual reporting rate was higher in 2009 (31.6 vs 16.6 VAE per 100,000 injections, respectively). The highest monthly incidence was observed in September 2009 (60.8 events per 100,000 injections). Two other peaks were observed in February 2008 and March 2009. The incidence in September 2009 was not significantly different from the incidences in February 2008 and March 2009. It was observed that incidence peaks occurred during influenza epidemic periods. One serious neurological VAE was observed.

CONCLUSIONS

The increase in seasonal influenza VAE in late 2009 mainly involved non-serious events, and could reflect stimulated reporting in the context of the A(H1N1)pdm09 pandemic. VAE reporting rates were highest during influenza epidemic periods, which could be explained by VAE being wrongly attributed to the vaccine when symptoms could reflect coincident background cases of viral infection.

Novel influenza A(H1N1) outbreak among French armed forces in 2009: results of Military Influenza Surveillance System

OBJECTIVES

An outbreak of novel A(H1N1) virus influenza, detected in Mexico in April 2009, spread worldwide in 9 weeks. The aim of this paper is to present the monitoring results of this influenza outbreak among French armed forces.

STUDY DESIGN

The period of monitoring by the Military Influenza Surveillance System (MISS) was 9 months, from May 2009 to April 2010.

METHODS

The main monitored events were acute respiratory infection (ARI), defined by oral temperature ≥38.5 °C and cough, and laboratory-confirmed influenza. Weekly incidence rates were calculated by relating cases to the number of servicepersons monitored.

RESULTS

In continental France, the incidence of ARI increased from September 2009, with a weekly maxima of 401 cases per 100,000 in early December 2009 according to MISS. Estimations of the incidence of consultations which could be related to novel A(H1N1) influenza ranged from 48 to 57 cases per 100,000.

CONCLUSIONS

The trends observed by MISS are compatible with French national estimations. The incidence of consultations which could be related to A(H1N1) influenza at the peak of the epidemic (194 cases per 100,000) was much lower than the national estimate (1321 cases per 100,000). This may be due to servicepersons who consulted in civilian facilities and were not monitored. Other explanations are the healthy worker effect and the younger age of the military population.

Adverse events following pandemic influenza vaccine Pandemrix® reported in the French military forces--2009-2010

BACKGROUND

In the face of the A(H1N1) 2009 influenza pandemic, in October 2009 the French military health service (SSA) initiated a large vaccination campaign with Pandemrix(®) vaccine in the military forces. The aim of this study was to describe vaccine adverse events (VAE) reported during this campaign.

METHODS

VAE and the number of people vaccinated were surveyed by the SSA Epidemiological network across all military forces during the campaign, from October 2009 to April 2010. For each case, a notification form was completed, providing patient and clinical information. Three types of VAE were considered: non-serious, serious and unexpected.

RESULTS

There were 315.4 reported VAE per 100,000 vaccinations. Vaccination and VAE incidence rate peaks coincided with influenza epidemic peak in early December. The number of injected doses was 49,138, corresponding to a 14.5% vaccination coverage among military personnel, and 155 VAE were reported, including 5 serious VAE (1 Guillain-Barre syndrome, 2 malaises and 1 convulsive episode). Most VAE were non-serious (97.1%). Among these, 6 cases of local, rapidly regressive paresthesia were observed.

DISCUSSION

The military VAE surveillance system constitutes the only observatory on benign VAE in France. The reporting rate was much higher after the pandemic vaccine than after the seasonal vaccine, which may be a reflection of stimulated reporting. This report provides a useful description of VAE among military personnel during a mass emergency vaccination program, showing that the tolerance of the pandemic vaccine appeared acceptable.