1 Swine Flu Shot Enough?
Single Swine Flu Shot Gives Immunity in Early Tests
Sept. 10, 2009 - Adults are immune to swine flu after just one shot
of vaccine, early test results suggest.
It's a surprise finding. Most experts expected that two shots of the vaccine
-- given three weeks apart -- would be needed.
Now vaccine supplies may go twice as far, and may start working twice as
fast as expected, suggests University of Washington researcher Kathleen M.
Neuzil, MD, MPH, chairwoman of the flu vaccine working group of
the Advisory Committee on Immunization Practices (ACIP), the independent panel
that recommends vaccine policy to the CDC.
"On the basis of these data, it would be appropriate to begin vaccination
with the use of one dose," Neuzil writes in an editorial accompanying a report
of the study rushed into online publication by The New England Journal of
Neuzil, a pediatrician, notes that children may still need two doses of the
vaccine. But she says vaccine supplies "should not be held in reserve to be
used for a second dose."
The finding comes from a clinical trial of the CSL H1N1 swine flu vaccine in Australia. Some
40% of the 195 million doses of swine flu vaccine purchased by the U.S. will be
made by CSL, although other makers' swine flu vaccine is expected to be equally
In the Australian study, Michael E. Greenberg, MD, MPH, and colleagues gave
the vaccine to two groups of adults, one group age 18 to 50 and the other age
50 to 64. Half of the subjects in each group got a 15-microgram doses of the
vaccine -- the same dosage being prepared for U.S. vaccines. The other half got
a double 30-microgram dose.
Of the 120 volunteers who got the lower dose, 116 -- 96.7% -- developed at
least the minimum level of anti-flu antibodies considered to be protective.
"The robust immune response to the H1N1 vaccine after a single dose was
unanticipated," Greenberg and colleagues note. "Much of the current global
pandemic planning is predicated on previous experience that two doses of
vaccine are required to elicit a protective immune response in populations that
are immunologically naive to a new influenza strain."
U.S. trials of swine flu vaccine are underway. It remains to be seen whether
these studies will support the Australian findings. Even then, larger studies
will be needed to know exactly how different people, at different ages and with
different health status, will react to the vaccine.
But Neuzil says that in the face of an ongoing pandemic, it's urgent to
deploy the vaccine as soon as possible.
"The desire to see all the available data must be balanced with the needed
to deploy vaccine quickly to reduce morbidity associated with the pandemic,"