US flu markers are still climbing steadily, with the virus linked to nine more deaths in children, the US Centers for Disease Control and Prevention (CDC) said on Friday in its weekly update.
The percentage of clinic visits for flulike illness has now been above the national baseline for 9 consecutive weeks. Last week the level rose to 5.2%, up from 4.8% reported the week before.
In Mammoth Lakes, the numbers of children being seen at the Sierra Park Pediatrics Clinic are still elevated above epidemic levels, although less than the peak which occurred in early January.
California is reporting decreasing influenza activity; however, flu activity is still widespread throughout the state.
Respiratory specimens testing positive are still mostly influenza A; however, the percentage of influenza B viruses found in samples rose from 12.3% to 16.7% last week. A shift toward more influenza B viruses is common for the latter part of the flu season. H3N2 is still the dominant strain, accounting for 93.6% of subtyped influenza A samples.
The CDC's maps show that flu is geographically widespread now in 46 states and Puerto Rico, an increase of 3 states from the previous week. High-intensity flu activity, another measure of clinic visits for flu, was reported for 28 states and New York City, reflecting an increase of 5 states compared with the week before.
Hospitalizations, deaths rise
Hospitalizations for flu are also increasing steadily, with the overall rate now at 29.4 per 100,000 population, the CDC said. The highest level is still in seniors, a group known to be hit hard by the H3N2 subtype. Compared with the previous week, the rate in that group rose from 113.5 to 136.6 per 100,000 population.
Thus far, there have been 50 deaths in persons <65 years of age in California. Deaths in persons >65 years of age are not tabulated.
Nationally, there were 9 new pediatric flu deaths last week, lifting the season's total to 29. The CDC started tracking pediatric flu deaths in the 2004-05 season, and totals have ranged from a low of 37 to a high of 171.
With the influenza season still in full swing, the CDC said that interim influenza vaccine effectiveness estimates suggest this year's vaccine protects roughly half (48%) of recipients. Although not ideal, getting vaccinated is still the single most important thing one can do to prevent infection. This year’s flu is mostly the H3N2 type, which is generally more severe, especially for the elderly and very young. Vaccine effectiveness for this type of flu is usually in the 30-50% range. Vaccine effectiveness was 43% against the predominant influenza A (H3N2) virus and 73% against illness caused by influenza B virus. Influenza A caused 88% of the cases studied, which mirrors the national trend.
Need for better vaccines
"These numbers are the new normal, and unfortunately I don't believe this is an acceptable normal," said Michael Osterholm, PhD, MPH, director of the Center for Infectious Disease Research and Policy at the University of Minnesota. "When we see these trends year after year, it should scream that we need a massive effort to replace the flu vaccine with something more effective."
While Dr. Belongia (author of the vaccine effectiveness study) said that there was a "glass half-full or half-empty" way to look at the numbers, he repeated the CDC's guidelines, which suggest anyone over 6 months still get vaccinated. As of Feb 3, the CDC said that approximately 145 million doses of influenza vaccine had been distributed.
"It's far better than having no protection at all," said Belongia. "And any reduction is having a big public health impact."
Belongia said the flu research community is aware that better vaccines need to be developed, but right now, "nothing is waiting in the wings to replace the current vaccine product."
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