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Michael Delgado
Mohamed Jama
BIOL-1615-010
10/29/2014
Climate change and influenza: the likelihood of early and severe influenza seasons following
warmer than average winters
Surveillance efforts have been made for years in the following of a sickness known as
influenza which is a viral infection of the respiratory passage that usually causes fevers and
severe headaches while typically occurring in epidemics. In 2011-12 the influenza season was
remarkably mild and late, which also set a new record as a season with the lowest and latest peak
of influenza-like illness (ILI). Several studies have been done and observed which have shown
that influenza dramatically decreases in warmer temperatures and high humidity. In contrast the
2012-13 season had an unusually early and quick start, even though the national climates were
pretty close to the seasonal average. The studies also find that the influenza virus is much more
severe and more likely to start earlier following a mild winter. Their works states there is usually
a pretty severe season of influenza following a mild influenza seasons during warm winters. This
information that was provided can help improve prevention efforts and create more advanced
vaccination programs to achieve a high rate vaccination coverage in advance of the following
influenza season.
For this study a lot of information was obtained from “The CDC website to obtain
weekly time series of laboratory – of confirmed influenza incidence recorded across ten US
geographic regions”. Information from the “CDC 122 Cities Mortality Reporting system” was
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used each season to record the mortality of influenza-related deaths. They calculated the
population weighted average climate across the US regions by obtaining information from the
US Census Bureau. Additional daily climate information was provided by the National Climate
Data Center (NCDC) of the National Oceanic and Atmosphere Administration (NOAA). These
studies helped show that during winter (January-March) and autumn (September-December) of
1997 to 2012 the average temperatures were all about the seasonal averages, but early winter of
2012 the temperature was significantly warmer whereas autumn of 2012 was back to its seasonal
average. This analysis of influenza examined the interaction between the initial growth rate and
weather temperatures, while also assessing the temperatures and growth rate the season before.
The study stated that the initial growth rates estimated for influenza A epidemics are on
average 15% higher compared to the estimates for influenza B, which these results provided are
in accordance to several previous studies. Mild winters were found to be associated with early
and severe epidemics the next season. After mild winters, on average 72% of the time the next
epidemic was more severe than average at an estimated growth rate 40% higher than average.
The peaking times of influenza occurred 11 days earlier and the likelihood of the peaking time
occurring before January 1st was higher than 80%. Their observations show that fewer people
will be infected due to warmer weathers therefore causing severe seasons of influenza following
warmer winters. They stated that these severe seasons can be prevented or helped by ensuring a
program that helps people receive vaccinations. The researcher’s results and studies find that
climate patterns can have a big impact on our society and influenza, which leave us with reason
of concern which is in need of more research and studies.