Flu in early life determines our susceptibility to future infections
New findings suggest early exposure to the flu affects how likely we are
to acquire future infections and may also impact vaccine effectiveness

Date:
July 7, 2020
Source:
eLife
Summary:
Early infections of influenza A can help predict how the virus
will affect people across different ages in the future and could
impact the effectiveness of flu vaccines, says a new study.



FULL STORY ========================================================================== Early infections of influenza A can help predict how the virus will
affect people across different ages in the future and could impact the effectiveness of flu vaccines, says a new study published today in eLife.


==========================================================================
The findings may help improve estimates of both the age-specific risk
of acquiring seasonal influenza infections and vaccine effectiveness in similarly vaccinated populations.

Seasonal influenza is an acute respiratory infection caused by
influenza viruses that occur across the world. It causes approximately 100,000-600,000 hospitalisations and 5,000-27,000 deaths per year in
the US alone. There are three types of seasonal influenza viruses in
humans: A, B and C, although C is much less common. Influenza A viruses
are further classified into subtypes, with the A(H1N1) and A(H3N2)
subtypes currently circulating in humans. A(H1N1) is also written as A(H1N1)pdm09 as it caused the 2009 pandemic and replaced the A(H1N1)
virus which had circulated before that year.

The rapid evolution of seasonal influenza that allows it to escape
preexisting immunity adds to the relatively high incidence of infections, including in previously infected older children and adults. But how susceptibility arises and changes over time in human populations has
been difficult to quantify.

"Since the risk of influenza infection in a given age group changes over
time, factors other than age may affect our susceptibility to infection,"
says first author Philip Arevalo, a postdoctoral researcher in senior
author Sarah Cobey's lab, Department of Ecology and Evolution, University
of Chicago, US. "We wanted to see whether these differences can be
explained in part by the protection gained from childhood flu infection,
which has lasting impacts on the immune response to future infections
and the protection against new influenza A subtypes." To measure the
effect of early exposures to seasonal influenza on risk and vaccine effectiveness, Arevalo and his team applied statistical models to flu
cases identified through seasonal studies of vaccine effectiveness from
the 2007-2008 to 2017-2018 seasons in the Marshfield Epidemiologic Study
Area (MESA) in Marshfield, Wisconsin, US. Each flu season, individuals in
a defined community group were recruited and tested for flu when seeking outpatient care for acute respiratory infection. Those eligible for the
study were individuals older than six months of age living in MESA and
who received routine care from the Marshfield Clinic.

Despite the extensive evolution in influenza A subtypes H1N1 and H3N2 over
the study period, the team's model showed that early infection reduces
the risk of people needing to seek medical attention for infections with
the same subtype later in life. This effect is stronger for H1N1 compared
to H3N2. The model also revealed that the effectiveness of flu vaccines
varies with both age and birth year, suggesting that this effectiveness
also depends on early exposure.

"We hope the findings from our study will improve our understanding of influenza epidemiology and the low and variable effectiveness of the
seasonal flu vaccine," concludes senior author Sarah Cobey, Principal Investigator at the Department of Ecology and Evolution, University of
Chicago. "This would lead to better forecasting and vaccination strategies
to help combat future flu seasons."

========================================================================== Story Source: Materials provided by eLife. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Philip Arevalo, Huong Q McLean, Edward A Belongia, Sarah
Cobey. Earliest
infections predict the age distribution of seasonal influenza
A cases.

eLife, 2020; 9 DOI: 10.7554/eLife.50060 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200707113304.htm

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