CDC. US: A report published in the January 16 Morbidity and Mortality Weekly Report
(MMWR) estimates that getting a flu vaccine this season reduced a
person’s risk of having to go to the doctor because of flu by 23 percent
among people of all ages.
Since CDC began conducting annual flu vaccine effectiveness (VE) studies in 2004-2005, overall estimates for each season have ranged from 10 percent to 60 percent effectiveness
in preventing medical visits associated with seasonal influenza
illness. The MMWR report says this season’s vaccine offers reduced
protection and this underscores the need for additional prevention and
treatment efforts this season, including the appropriate use of influenza antiviral medications for treatment.
“Physicians
should be aware that all hospitalized patients and all outpatients at
high risk for serious complications should be treated as soon as
possible with one of three available influenza antiviral medications if
influenza is suspected, regardless of a patient’s vaccination status and
without waiting for confirmatory testing,” says Joe Bresee, branch
chief in CDC’s Influenza Division. “Health care providers should advise
patients at high risk to call promptly if they get symptoms of
influenza.”
One factor that determines how well a flu vaccine
works is the similarity between the flu viruses used in vaccine
production and the flu viruses actually circulating. During seasons when
vaccine viruses and circulating influenza viruses are well matched, VE
between 50 and 60 percent has been observed. H3N2 viruses have been
predominant so far this season, but about 70 percent of them have been
different or have “drifted” from the H3N2 vaccine virus. This likely
accounts for the reduced VE.
Flu viruses change constantly and the
drifted H3N2 viruses did not appear until after the vaccine composition
for the Northern Hemisphere had been chosen.
Another factor that
influences how well the flu vaccine works is the age and health of the
person being vaccinated. In general, the flu vaccine works best in
young, healthy people and is less effective in people 65 and older. This
pattern is reflected in the current season early estimates for VE
against H3N2 viruses. VE against H3N2 viruses was highest -- 26 percent
-- for children age 6 months through 17 years. While not statistically
significant, VE estimates against H3N2 viruses for other age groups were
12 percent for ages 18 to 49 years and 14 percent for people age 50
years and older.
CDC recommends that people get a flu vaccine even
during season’s when drifted viruses are circulating because
vaccination can still prevent some infections and can reduce severe
disease that can lead to hospitalization and death. Also, the flu
vaccine is designed to protect against three or four influenza viruses
and some of these other viruses may circulate later in the season. Flu
activity so far this season has been similar to the 2012-2013 flu
season, a “moderately severe” flu season with H3N2 viruses
predominating.
Antiviral Supply Update
While
manufacturers of antiviral medications have stated that there is no
national shortage of antiviral medications at this time, and that there
is sufficient product available to meet high demand, there are anecdotal
reports of spot shortages of these drugs. CDC’s advice for patients and
doctors is that it may be necessary to contact more than one pharmacy
to fill a prescription for an antiviral medication. Pharmacies that are
having difficulty getting orders filled should contact their distributor
or the manufacturer directly.
For large institutional outbreaks
this season, CDC is taking new measures to help match demand with
supply, working with commercial partners to facilitate filling of large
orders of antivirals for long-term care facilities or institutions
having difficulty accessing antiviral supplies in outbreak settings.
More information is available at http://www.cdc.gov/flu/antivirals/supply.htm.