Military Study Shows Prevention of Novel A/H1N1 Virus Infection is Vaccine-Type and Age-Dependent
Both Live, Attenuated Influenza Vaccine (LAIV) and Trivalent Inactivated Vaccine (TIV) provide Protection against novel A/H1N1, especially against severe disease
WASHINGTON, Nov. 19 /PRNewswire/ -- Immunization with either
live attenuated influenza vaccine (LAIV, also known as
FluMist®), or trivalent inactivated influenza vaccine (TIV),
appears to offer a protection (~ 45%) against the novel A/H1N1
virus, the cause of the present influenza pandemic. However, the
benefit was largely attributed to the youngest age group. The
finding emerges from an evaluation of medical encounters and
seasonal influenza immunization of U.S. military service
members.
As reported today in a Late-Breaker presentation at the 58th
annual meeting of the American Society of Tropical Medicine and
Hygiene (ASTMH), seasonal influenza vaccination also appears to
offer higher protection against severe disease requiring
hospitalization (~ 62%, 95% confidence interval [CI], 14% to 84%)
than against milder infections that can be treated on an outpatient
basis (~ 42%, 95% CI, 29% to 53%).
"The increasing momentum of the H1N1 pandemic underscores the
need for vaccination, yet there is a wide variance in vaccine
effectiveness depending on the strain-match for a particular
season," comments Col. (Ret.) Jose L. Sanchez, MD, MPH, of the
Armed Forces Health Surveillance Center (AFHSC) in Silver Spring,
Maryland.
Dr. Sanchez and colleagues conducted a case control analysis of
influenza-related medical encounter data of U.S. military service
members, compared to a control group of personnel with acute,
non-respiratory illnesses. For the period of April-October 2009, a
total of 1,205 cases of pandemic H1N1 2009 infections were
reported, of which 966 (80%) were among males and more than
one-half (58%) were among those younger than 25 years. The overall
vaccine effectiveness (VE) for service members was found to be 45%
(95% confidence interval [CI], 33% to 55%). Immunization with prior
season's TIV (VE=37%; 95% CI, 23% to 49%) as well as LAIV (VE=22%;
95% CI, 1% to 38%), were found to be protective.
Interestingly, and unexpectedly, the investigators observed a
U-shaped relationship of VE with age stratification. VE was high in
the youngest (< 25 yo) and oldest (> 39 yo) service members
(50% and 55% respectively), while there was noVE for those 25 to 39
years of age.
"These data highlight the need for concise, timely assessments
of influenza vaccine effectiveness against the new A/H1N1 as well
as seasonal strains," notes Thomas Wellems, MD, PhD, president of
ASTMH. "Although the United States military constitutes a highly
immunized population that may not be generalizable to civilians, it
offers unique cohorts of at-risk individuals that can be studied in
randomized clinical trials. We look forward to further data from
this population."
"These findings suggest that while prior season's influenza
vaccine may not prevent infection or developing illness once
infected, it certainly appears to protect against more severe
outcomes. We may also be seeing a cross-protective effect resulting
from natural influenza infections and/or prior influenza
immunization in the military setting," says Dr. Sanchez. "This may
play a role in conferring a certain degree of 'immunological
priming."
"Continued timely assessment of influenza vaccine effectiveness
among military personnel is a top priority for us at the AFHSC. At
the very least, our results will assist health officials in the
military and Department of Defense in guiding future policy on
seasonal and novel A/H1N1 vaccine use among military service
members and dependents," Dr. Sanchez concludes.
About the ASTMH
The American Society of Tropical Medicine and Hygiene (ASTMH),
founded in 1903, is a worldwide organization of scientists,
clinicians and program professionals whose mission is to promote
global health through the prevention and control of infectious and
other diseases that disproportionately afflict the global
poor.
Source: The American Society of Tropical Medicine and Hygiene
CONTACT: Christina Witz, MWW Group, +1-646-509-9379, cwitz@mww.com
Posted: November 2009
