Researchers from the British Columbia Centre for Disease
Control observed suboptimal vaccine effectiveness against the influenza A/H3N2
virus during the 2010-2011 winter season and also detected genetic variants to
the virus using a sentinel surveillance platform.
During this time frame, there were many outbreaks
related to influenza A/H3N2 at long-term care facilities in Canada. The
outbreaks also affected vaccinated staff. Interim data from the sentinel
surveillance system, which incorporated genotypic, phenotypic and epidemiologic
indicators, identified genetic variants and suboptimal vaccine effectiveness.
“Unlike other vaccines, the influenza vaccine must
be reformulated and re-administered each year to keep pace with ongoing changes
in circulating virus strains,” Danuta Skowronski, MD, epidemiology
lead of Influenza & Emerging Respiratory Pathogens at BC Centre for Disease
Control, told Infectious Disease News. “For this reason, real-time
monitoring of circulating strains, their relatedness to chosen vaccine
components and their impact on vaccine protection are important. To do this
requires the efficient harnessing of molecular, individual and population-level
The researchers analyzed nasal/nasopharyngeal swabs and
epidemiologic data from 1,718 participants who presented with influenza-like
illness. Among these participants, 93 tested positive with A(H1N1)pdm09, 408
had A/H3N2 and 199 had influenza B. Patients who tested negative for influenza
were considered controls. Among the cases, 16% received the influenza vaccine
and among the controls, 24% received the vaccine.
The vaccine efficacy for adults aged 20 to 49 years was
65% for A(H1N1)pdm09 and 66% for influenza B. For A/H3N2, however, the vaccine
efficacy was only 39%.
Two hundred thirty-three specimens were isolated for
hemagglutination inhibition characterization. This process showed that all of
the A(H1N1)pdm09 isolates were A/California/7/2009-like and all of the A/H3N2
isolates were A/Perth/16/2009-like, demonstrating that all of the isolates were
well matched to the vaccine. However, on phylogenetic analysis, only two of the
A/H3N2 isolates belonged to the A/Perth/16/2009 vaccine clade. Most belonged to
the A/HongKong/2121/2010 variant, and the remainder belonged to the
A/Victoria/208/2009 variant, both of which were not matched to the vaccine.
“Understanding influenza virus evolution and its
impact on vaccine effectiveness real time can help inform adjunct prevention
and treatment measures when suboptimal vaccine protection is identified,”
Skowronski said. “Having a systematic platform to collect influenza
viruses and accurately assess their impact on vaccine effectiveness is
important in selecting new strains to be included in revised formulations each
Skowronski DM. Clin Infect Dis. 2012;55:332-342.
The researchers report financial
relationships with Becton Dickinson, Gen-Probe, GlaxoSmithKline,
Hoffmann-LaRoche, Merck, Pfizer, Roche, Sanofi-Pasteur and Siemens.