During week 1 (Dec 30-Jan 5), influenza activity remained elevated in the U.S., but may be decreasing in some areas – CDC FluView
# 6848
Based on recent media reports and online chatter, the two big topics of interest regarding this year’s flu season have centered around just how much flu is really out there, and whether this year’s flu vaccine has been a good match.
Today, with the release of the latest CDC FluView report and a special MMWR Early Release on this year’s Vaccine Effectiveness (VE) rating, we have some mid-season answers.
First from the MMWR, we get an unusually early evaluation of this year’s flu vaccine (made possible by the early onset of the flu season) which has calculated the vaccine effectiveness at 62%.
This number is basically in line with what the 2011 study, A Comprehensive Flu Vaccine Effectiveness Meta-Analysis by Michael T. Osterholm and his team at CIDRAP, found:
TIV showed efficacy in preventing influenza during 8 of 12 flu seasons (67%) with a combined efficacy of 59% among healthy adults (aged 18–65 years).
And among children aged 2-7, the LAIV proved even more protective, showing efficacy in 9 out of 12 flu seasons (75%) with a pooled efficacy of 83%.
The entire MMWR report is available at:
Early Estimates of Seasonal Influenza Vaccine Effectiveness — United States, January 2013
The results are summarized in:
What is already known on this topic?
In the United States, annual vaccination against seasonal influenza is recommended for all persons aged ≥6 months. An overall moderate effectiveness for influenza vaccines of approximately 60% has been estimated from a summary of randomized clinical trials. Influenza vaccination, even withmoderate effectiveness, can reduce illness, antibiotic use, doctor visits, time lost from work, hospitalizations, and deaths.
What is added by this report?Based on data from 1,155 children and adults with acute respiratory illness enrolled during December 3, 2012–January 2, 2013, at five study sites with outpatient medical facilities in the United States, the overall estimated effectiveness of the 2012–13 seasonal influenza vaccine for preventing medically attended, laboratory-confirmed influenza virus infection was 62%.
What are the implications for public health practice?
Interim VE estimates indicate the 2012–13 influenza vaccine has moderate effectiveness against circulating influenza viruses, similar to a summary estimate from randomized clinical trials.
Vaccination efforts should continue as long as influenza viruses are circulating. Any persons aged ≥6 months who have not received vaccination this season should be vaccinated. However, some vaccinated persons will become infected with influenza. Therefore, antiviral medication should be used as recommended for treatment in patients regardless of their vaccination status.
As far as the severity and extent of this years flu season, today’s FluView Report shows some signs that influenza may have peaked in a few states, while other states are still on the ascendant. Some of these trends may be influenced by reduced reporting over the holidays.
Just under 1/3rd of samples tested last week proved positive for influenza (A or B), with influenza A/H3N2 far in the lead, followed by Influenza B, and A/H1N1pdm09 scarcely registering.
2012-2013 Influenza Season
Week 1 ending January 5, 2013
As a result of the end of year holidays and elevated influenza activity, some sites may be experiencing longer than normal reporting delays and data in previous weeks are likely to change as additional reports are received.
Synopsis: During week 1 (December 30-January 5), influenza activity remained elevated in the
U.S., but may be decreasing in some areas.
- Viral Surveillance: Of 12,876 specimens tested and reported by U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories, 4,222 (32.8%) were positive for influenza.
- Pneumonia and Influenza Mortality: The proportion of deaths attributed to pneumonia and influenza (P&I) was slightly above the epidemic threshold.
- Influenza-Associated Pediatric Deaths: Two influenza-associated pediatric deaths were reported. One was associated with an influenza A (H3) virus and one was associated with an influenza A virus for which the subtype was not determined.
- Outpatient Illness Surveillance: The proportion of outpatient visits for influenza-like illness (ILI) was 4.3%; above the national baseline of 2.2%. Nine of 10 regions reported ILI above egion-specific baseline levels. Twenty-four states and New York City experienced high ILI ctivity; 16 states experienced moderate ILI activity; 5 states experienced low ILI activity; 5 states experienced minimal ILI activity, and the District of Columbia had insufficient data.
- Geographic Spread of Influenza: Forty-seven states reported widespread geographic
influenza activity; 2 states reported regional activity; the District of Columbia reported local activity; 1 state reported sporadic activity; Guam reported no influenza activity, and Puerto Rico and the U.S. Virgin Islands did not report.
Despite a good deal of speculation in the media that a new strain of flu may have crept into the mix, this week’s report indicates that only 2 (out of 327 H3N2 viruses tested) showed reduced titers with antiserum produced against the A/Victoria/361/2011 vaccine strain.
Among those hospitalized with laboratory confirmed influenza, those over 65 (as is normally expected) constitute the majority of cases, followed next by children under the age of 4 (again the normal seasonal pattern).
So, based on these numbers, so far we are seeing a moderately severe – but hardly unprecedented – flu season. And this year’s vaccine appears to be about average in its effectiveness against the strains in circulation.
But the flu season isn’t over until the flu seasons is over.
While there is a pressing need for better flu vaccines (see CIDRAP: The Need For `Game Changing’ Flu Vaccines) the vaccines we have today do provide a moderate level of protection.
Which, while not as good as we’d like, is far better than nothing. Beyond the vaccine, the CDC recommends:
Take everyday preventive actions to stop the spread of germs.
- Cover your nose and mouth with a tissue when you cough or sneeze. Throw the tissue in the trash after you use it.
- Wash your hands often with soap and water. If soap and water are not available, use an alcohol-based hand rub.*
- Avoid touching your eyes, nose and mouth. Germs spread this way.
- Try to avoid close contact with sick people.
- If you are sick with flu–like illness, CDC recommends that you stay home for at least 24 hours after your fever is gone except to get medical care or for other necessities. (Your fever should be gone without the use of a fever-reducing medicine.)
- While sick, limit contact with others as much as possible to keep from infecting them.
