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Two influenza strains not protected with the influenza vaccine
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Recent data from the influenza division of the CDC indicated that protection from both the influenza A H3N2 and B virus strain in the community may not be optimal.
“Ninety-three percent of the B strains we are seeing are in a different lineage than the vaccine strain and approximately 35% are type A (H3N2). It is important to remember that although a less-than-ideal virus match between the viruses in the vaccine and those in the circulating viruses can reduce vaccine effectiveness, we know from past influenza studies that the vaccine can still protect enough to make illness milder or prevent influenza-related complications,” Joe Bresee, MD, chief of the epidemiology and prevention branch at the CDC’s influenza division, said during a recent CDC news conference.
According to Bresee, although seasonal influenza activity had a slow start this year, it has increased in recent weeks.
At press time, influenza was widespread in 31 states, 17 states reported regional influenza and local influenza was reported in two remaining states and in the District of Columbia.
The CDC’s influenza lab also recently reported that 4.5% of overall viruses reported in the United States are resistant to oseltamivir (Roche, Tamiflu).
“All the resistant viruses are among the subtype A (H1N1). We have not seen any resistance yet among the A (H3N2) viruses or among the B viruses that we tested this year and no resistance has been found to zanamivir (GlaxoSmithKline, Relenza),” Bresee said.
“Remember that although vaccination is the best way to prevent influenza and is our primary tool, the CDC recommends that people practice other protective measures like hand hygiene and cough etiquette as well as the appropriate use of antiviral drugs,” he said.
The CDC has tracked the pediatric deaths from influenza-related complications starting from the 2003-2004 influenza season and since then, the annual number of confirmed child influenza deaths have ranged from 44 to 153. As of this February, six child deaths from influenza have been reported to the CDC.
“If you compare this with the previous four years for which we have done active or passive pediatric death surveillance, this is a relatively low number. But again, we are just on the upswing of the influenza season and this certainly may change,” he said.
In reality, if one looks back carefully in this decade, almost every other year the experts have mismatched the influenza strain target for one of three strains in the vaccine. Sadly, no one bestowed upon them soothsayer powers for this daunting decision. Thus, the bad news: once again the injectable vaccine will provide marginal protection for about half the patients this year and they will still get the flu. But the good news: the severity and duration will be blunted for most. More good news: a documented way to circumvent this antigenic drift problem, at least in pediatric patients without a history of significant wheezing, is to use the cold-adapted nasal influenza vaccine. Three different studies have confirmed that it has excellent coverage (~87%) when influenza strains show antigenic drift. And in children, half as many post vaccine influenza failures occur with the nasal vaccine as opposed to the shot. And one nasal dose is 90% effective for vaccine-naive children — and with two nasal doses, efficacy lasts more than a year or two. Alas the bad news, we could not get the nasal vaccine during the early fall months this year because the federal government gobbled up the entire initial few months of supply and the FDA didn not approve it for children aged 12-24 months because of the slight increase in wheezing episodes in the clinical trials, despite high efficacy.
– Stan Block, MD
IDC Editorial Advisory Board Member