CDC and Vaccine candidates As of Fri 10 May 2013, sporadic human cases of infection with avian
influenza A (H7N9) continue to be reported in China, but the increase
in case counts has fallen off from the month of April 2013, when
multiple cases were being reported each day.
The drop-off in newly reported H7N9 cases in China may be the result
of containment measures reportedly taken by Chinese authorities,
including closing live bird markets, a venue where the risk of
exposure to bird flu viruses can be high. However, it may also be a
result of changing seasons or a combination of both. Studies indicate
that avian influenza viruses have a seasonal pattern to them, much
like human seasonal influenza viruses.- increase in the winter and decline in the summer.
It's possible that the same will be true with H7N9 and that as H7N9
activity in poultry or other birds declines, so will the chances for
human exposures and resulting human infections. If this is the case,
H7N9 infections -- in birds and people -- may pick up again when the
weather turns cooler.
While the number of human infections being reported has dropped, the
epidemiology of the current outbreak has not changed significantly.
Evidence continues to point to infected poultry or contaminated
environments as the source of most infections. There is still no
evidence of sustained (ongoing) human-to-human transmission with this
virus, and no cases have been reported outside of China.
While the risk to people in the United States from H7N9 continues to
be low, because of the pandemic potential posed by this virus, CDC is
following this situation closely and coordinating with domestic and
international partners, including the Chinese Center for Disease
Control (China CDC) and the World Health Organization (WHO). CDC also
is taking proactive steps to be ready for the possibility that this
virus may become fully transmissible between people.
Shipping of the CDC-developed H7N9 diagnostic test kits began on 25
Apr 2013. By 10 May 2013, 122 test kits had been shipped, 95 of these
domestically and 27 of them internationally. At this time, test kits
have been shipped to 47 U.S. states and the District of Columbia. Each
kit is able to test about 1000 specimens for H7N9. Public health
laboratories are being asked to rule out seasonal influenza before
they use the H7N9 test kits. CDC's seasonal flu diagnostic tests will
produce an influenza A "unsubtypable" result on an H7N9 sample. The
new kits will allow H7N9 to be detected much more rapidly than if all
"unsubtypable" samples had to be sent to CDC for testing, thus
enhancing the country's ability to quickly detect this virus in the
U.S.
While no cases of H7N9 have been detected at this time in the U.S., 54
people with flu-like symptoms after travel to China have been tested.
All 54 have tested negative for H7N9, while 6 tested positive for
seasonal influenza A, and 3 tested positive for seasonal influenza B.
Should a case be detected in the United States, this would not signal
an increase in the potential risk to the public's health unless the
transmission pattern of the virus was to change. If a person in the
United States has H7N9 flu, they will be isolated (separated from
other people who are well) and cared for. In addition, a contact
investigation will be done with people who may have been exposed to
the sick person.
Contact investigations are one of the ways CDC works with partners in
the United States and other countries to protect the health of people
exposed to an illness. This process involves finding, interviewing,
and in some cases, testing or treating the people who came into
contact with the sick person. All of this can help confirm that the
virus is not spreading further in the United States.
At this time, a decision to produce H7N9 vaccine for a U.S. national
vaccination response has not been made. However, given the severity of
human illnesses from H7N9 in China, HHS and its partners are taking
preparedness steps to develop H7N9 candidate vaccine viruses and are
planning for H7N9 vaccine clinical trials. CDC is working on
developing candidate vaccine viruses (CVVs) from 2 different H7N9
isolates (Shanghai/2 and Anhui/1). A CVV is a flu virus that CDC (or
one of the other WHO Collaborating Centers) selects and prepares for
use by vaccine manufacturers to make a flu vaccine. These CVVs could
be used to manufacture vaccine if one is needed. Candidate vaccine
viruses are typically chosen based on their similarity to flu viruses
spreading and causing illness in people as well as their ability to
grow easily in chicken eggs, which is the primary method of
manufacturing influenza vaccine. Without a high-yield candidate
vaccine virus, it can be very difficult to manufacture vaccine to
protect against a new influenza virus. Once a vaccine manufacturer
receives a candidate vaccine virus, manufacturers then create what is
known as a "seed strain." The seed strain is adapted by each
manufacturer to make the virus grow better using their technology and
production systems. Once the seed strain is prepared, the vaccine
manufacturer uses it to grow large quantities of virus for producing
flu vaccine.
On 1 May 2013, CDC offered to begin shipping potential candidate
vaccine viruses to qualified laboratories with biosafety-level 3
facilities that wanted to begin working on creating their own seed
virus early. These are candidate vaccine viruses that still require
some in vitro and in vivo studies to be completed to meet full
regulatory and biosafety requirements. Other WHO partners have
potential candidate vaccine viruses as well. Neither the World Health
Organization or the U.S. Food and Drug Administration have made any
recommendation about which H7N9 potential candidate vaccine virus is
recommended for use in the manufacture of H7N9 vaccine.
It's important to note that influenza vaccine production is complex
and can be unpredictable and has many critical and time-sensitive
steps; delay at any point during these steps can result in delays in
the availability of influenza vaccine. However, it usually takes about
6 months to produce large quantities of influenza vaccine.