14 R&D Magazine APRIL 2019 www.rdmag.com
An imperfect vaccine
The seasonal flu vaccine has been key to preventing wide
spread flu infection since it was first approved in 1945.
However, despite its benefits, the vaccine is far from perfect.
“Current influenza vaccines, although they have
extraordinary value at avoiding morbidity and mortality, are
nonetheless, not consistently effective,” said Fauci, during the
AAAS scientific session. “This year, thus far we have about 47
percent efficacy, last year—one of the worst years that we’ve
had in many years—the overall efficacy was about 40 percent
and the efficacy against H3N2, the predominant strain, was
In the last 15 years, the highest flu vaccine efficacy reported
was 60 percent during the 2010-2011 season. Efficacy
dropped as low as 10 percent in 2004, according to the CDC.
During the presentation at the AAAS Annual Meeting,
Messonnier noted that while these numbers are discouraging,
it is important to remember that even low vaccine efficacy
makes a big difference.
“Even a small amount of vaccine effectiveness can save lots
of lives and prevent lots of hospitalizations,” she said.
A complex virus
Creating a flu vaccine is no easy task. The virus is extremely
complex and is constantly mutating to avoid host immunity.
There are 18 different subtypes of Influenza A and two subtypes
of Influenza B, and each subtype has many, many strains.
“There are literally thousands of strains that we know of,”
said Nabel, during the AAAS Annual Meeting scientific
session. “This is one of the reasons that it is such a challenge
to create a vaccine against a genetically diverse and biochem-
ically diverse set of targets.”
Selecting which strains
to target each year is one
of the CDC’s biggest
The CDC looks at
which strains of the flu
are circulating outside of
the U.S. and tests over one
million patient specimens
in clinical labs within the
This long timeline is sometimes the cause of lower vaccine
efficacy, said Fauci.
“You can have an antigenic mismatch, which is a well-known case of decreased influenza seasonal vaccines,” said
Fauci. “In other words, you make your choice in February or
March about what virus is going to be in the vaccine, but in
the six or seven month period that you are growing it, there
is a possibility that in nature, it will mutate and while you are
making a vaccine for A, the virus turns to B.”
More than 1 million patient specimens are tested
in clinical labs participating in CDC domestic
About 100,000 specimens are tested
in 93 state/local public health labs.
CDC conducts full genetic sequencing
on about 7,000 flu viruses each year.
CDC tests about 2,000 flu
viruses to determine their
CDC prepares as
many as 50 viruses
for possible use in
*2017-2018 influenza data as reported by CDC’s Influenza Division,
National Center for Immunization and Respiratory Diseases (NCIRD)