Influenza has reached epidemic proportions in the US, the Centers for Disease Control and Prevention (CDC) reported this week, as 2014 ended with 15 children reported killed by the virus.
Since 28 September, experts at the federal agency have confirmed 28,218 cases of influenza around the US. Thirty-six states reported widespread virus activity, 22 of them experiencing high infection rates and nine reporting deaths.
The south and midwest have had a particularly tough season, with three deaths in Texas and hospitals issuing warnings to parents in Michigan and Kansas.
Only halfway through the flu season, the CDC predicts influenza strains will infect every state and US territory by the end of spring. It cautioned, however, that the 2014-15 flu season should not yet be compared with previous years.
Dr Michael Jhung, one of the CDC’s experts on influenza, told the Guardian there was no reason yet to believe that the 2014-15 flu season is unusual. “We are in an epidemic of flu, but we have epidemics of flu every year,” he said.
The flu crosses the threshold of epidemic levels almost every year in the US, as strains mutate and the CDC rolls out new vaccines to meet the changed viruses. As of the CDC’s last assessment, the current flu season is at the threshold of an epidemic.
“There’s a suggestion that it may be a more severe season,” Jhung said, since “the most common virus of this season, the H3N2 virus, has been associated with more severe seasons in the past.”
Jhung characterized those H3N2 years as “moderately severe”, and said this season was shaping up to look like those years. But he cautioned that the flu season could change dramatically before the end of May.
“The common line of ‘If you’ve seen one flu season then you’ve seen one flu season’ really applies,” he said. “Things could change in the next week or the next month, and we could end up with a mild season, or with a different dominant virus.”
In December, the CDC warned that this year’s flu vaccine would be less effective than usual due to a strain’s mutation during the production of the shot. Agency director Dr Tom Frieden advised hospitals that the season could be more severe, since the vaccine, which covers several variants, is a mismatch with the virus circulating most widely.
Flu seasons tend to be unpredictable: in the past decade as few as 37 people have died one season and as many as 171 the next. In only one year in recent memory has influenza reached pandemic proportions, when the strain of H1N1 “swine flu” swept through the US in 2009. That year, as in 2014, variant strains “drifted” genetically and antigenically – meaning they mutated to evade a host’s defenses – at just the right time to slip past researchers developing a vaccine.
The CDC helped decide what would be in this year’s flu vaccine in February, and production takes about four months; the H3N2 strain mutated just enough in March to reduce the vaccine’s effect.
“The vaccine’s different, but similar enough so there’s protection afforded,” Jhung said, “and it will still provide very good protection for the other flu viruses still out there.”
The CDC will not know until April or May whether the 2014-15 season is worse than others, because deaths and hospitalizations are only two means of gauging a season and are reported slowly, and because the CDC does not require hospitals report adult deaths. For that reason, the CDC says it may simply be an unusually early season, rather than a more severe one.
This year’s dominant strain of H3N2, however, does “tend to have more hospitalizations and more deaths”, Frieden warned in December.
With months left before infections wane and a few strains well protected by the vaccine, Jhung recommended that people at risk – children under two, adults over 65 and people with medical conditions – quickly get antiviral medications from a doctor should they fall ill with the flu.
Such medications “work to prevent the virus from replicating in the body”, he said, meaning that the flu can be kept in check before it has a chance to overwhelm an already vulnerable immune system.
Most children who die from influenza-related causes were not vaccinated, the CDC has found.
Frieden advised in December that preventative measures as simple as staying home would help reduce infection rates and be better for sick people.
.jpg?w=600)
