Post-pandemic influenza-associated mortality in Mexico.

Influenza is a leading cause of respiratory tract infections worldwide and there is limited information on the impact of the influenza A(H1N1)pdm virus on mortality after the 2009 pandemic. Using national mortality register data through 1998-2015 in Mexico, influenza-associated mortality was estimated for respiratory, cardiovascular, and all-cause events. The proportion of influenza-associated respiratory and cardiovascular deaths among different age groups were compared. There were 8,853,986 death registries included for the 1998-2015 winter seasons, average influenza-associated respiratory, cardiovascular, and all-cause mortality rates were 5.2, 6.3, and 19.6 deaths/100,000 population, respectively. The largest number of respiratory influenza-associated deaths occurred in adults 60 years of age and older, followed by children <5 years of age; during the 2009 pandemic, 2011-2012, and 2013-2014 winter seasons there was a larger number of deaths in the 20-59 years old group. Influenza-associated mortality rates showed a continuous reduction in children <5 years of age. After the 2009 pandemic, influenza A(H1N1)pdm09 virus-associated mortality in Mexico showed a persistent change in the demographic pattern of the most severely affected population, particularly during the 2013-2014 season. Influenza associated-mortality has decreased in children <5 years of age and continue to be elevated in adults >60 years of age.

Impact of vaccination on influenza mortality in children <5years old in Mexico.

BACKGROUND: Influenza is a leading cause of respiratory tract infections among children. In Mexico, influenza vaccination was included in the National Immunization Program since 2004. However, the population health effects of the vaccine on children have not been fully described. Thus, we estimated the impact of influenza immunization in terms of mortality associated with this virus among children younger than 5years of age in Mexico. METHODS: Mortality rates and years of life lost associated with influenza were estimated using national mortality register data for the period 1998-2012. Age-stratified and cause-specific mortality rates were estimated for all-cause, respiratory and cardiovascular events. Influenza-associated mortality was compared between the period prior to introduction of the influenza vaccine as part of the National Immunization Program (1998-2004) and the period thereafter (2004-2012). RESULTS: During the 1998-2012 winter seasons, the average number of all-cause, respiratory and cardiovascular deaths attributable to influenza were 1186, 794 and 21, respectively. Influenza-associated mortality was higher prior to the vaccination period than after influenza was included in the immunization program for all-cause (mean 1660 vs. 780) and respiratory (mean 1063 vs. 563) mortality, but no reduction was seen for cardiovascular mortality. The proportion of all-cause and respiratory deaths attributable to influenza was significantly lower in the post-vaccine period compared with the pre-vaccine period (P<0.001), but no reduction was seen in the proportion of cardiovascular deaths. There was an average annual reduction of 66,558years of life lost in the post-vaccine compared with the pre-vaccine period. CONCLUSION: The introduction of influenza vaccination within the Mexican Immunization Program was associated with a reduction in mortality rates attributable to this virus among children younger than 5years of age.