Abstract
Influenza outbreaks have been of relatively limited historical interest in Mexico. The 2009 influenza pandemic not only changed Mexico's health priorities but also brought to the forefront some of the strengths and weaknesses of Mexico's epidemiological surveillance and public health system. A year later, Mexico's data show an epidemic pattern characterized by three "waves''. The reasons this three-wave patterns are theoretically investigated via models that incorporate Mexico's general trends of land transportation, public health measures, and the regular opening and closing of schools during 2009. The role of vaccination is also studied taking into account delays in access and limitations in the total and daily numbers of vaccines available. The research in this article supports the view that the three epidemic "waves" are the result of the synergistic interactions of three factors: regional movement patterns of Mexicans, the impact and effectiveness of dramatic social distancing measures imposed during the first outbreak, and the summer release of school children followed by their subsequent return to classes in the fall. The three "waves" cannot be explained by the transportation patterns alone but only through the combination of transport patterns and changes in contact rates due to the use of explicit or scheduled social distancing measures. The research identifies possible vaccination schemes that account for the school calendar and whose effectiveness are enhanced by social distancing measures. The limited impact of the late arrival of the vaccine is also analyzed.
Highlights
We live in a highly interconnected world where individuals move between cities, states, countries, and continents in a matter of hours
The simulated total of infective and the data for the first wave were normalized by their peaks so that both had a maximum of 1. It is worth remark at this point that the data examined does not let us test whether or not some populations in Mexico were more susceptible to the novel AH1N1pdm virus
The mechanism of suppression and recovery of the infection rates described in the last paragraphs was used again, in this case with sharp slopes representing the sudden changes in transmission that may occur during closure and reopening of schools. These results suggest that the implementation of measures that decrease the contact rates in combination with the school calendar, as it was the case in Mexico, can have a significant mitigating effect on the spread of the influenza
Summary
We live in a highly interconnected world where individuals move between cities, states, countries, and continents in a matter of hours. To test if land transport could be responsible for the delay observed in the epidemic outbreaks reported in the different Mexican States, simulations with the system (1)-(14) were conducted assuming different contributions of the strongly and weakly connected States (q and 1 − q, respectively) to the total daily flow from and to Mexico City (Fig. 6).
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