While influenza vaccines are considered to be the best protection against catching the flu, we know that their effectiveness can vary widely from one year to the next, and by the age and immune response of individual recipients.
It has long been problematic that flu shots must be formulated 6 months before they can be rolled out, and during that time the flu viruses in circulation can change antigenically, making the vaccine a less exact match.
In truth, we really don’t know how well any particular flu vaccine will work until the flu season is over, and the data is analyzed.
Last year, in CIDRAP: A Comprehensive Flu Vaccine Effectiveness Meta-Analysis, we took an extended look at a study conducted by researchers at CIDRAP, along with colleagues from the Marshfield Clinic Research Foundation and Johns Hopkins University.
After an exhaustive examination of more than 5,700 published studies - going back to 1967 - fewer than 3 dozen studies met their (admittedly strict) criteria.
While large gaps in the data remain, they were able to determine:
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%.
While finding flu vaccines `moderately protective’, the study’s authors cautioned that their findings should be seen as a clarion call for the development of more effective influenza vaccines.
Today, another study, this time appearing in the journal Clinical Infectious Diseases, that attempts to put a VE (Vaccine Effectiveness) rating on the flu vaccine for the the 2010-11 flu season.
Based on a case–controlled study of nearly 4,800 patients, they compared vaccination histories and positive RT-PCR testing for influenza, and came up with an overall adjusted VE of 60% (95% [CI], 53%–66%).
Children aged 6-months to 8 years came in with a VE of 69% (95% CI, 56%–77%) while adults > 65 came in at a disappointing 38% (95% CI, −16% to 67%).
Effectiveness of Seasonal Influenza Vaccines in the United States During a Season With Circulation of All Three Vaccine Strains
John J. Treanor, H. Keipp Talbot, Suzanne E. Ohmit, Laura A. Coleman, Mark G. Thompson, Po-Yung Cheng, Joshua G. Petrie, Geraldine Lofthus1, Jennifer K. Meece, John V. Williams, LaShondra Berman, Caroline Breese Hall, Arnold S. Monto, Marie R. Griffin, Edward Belongia, David K. Shay
Conclusions. The US 2010–2011 influenza vaccines were moderately effective in preventing medically attended influenza during a season when all 3 vaccine strains were antigenically similar to circulating viruses. Continued monitoring of influenza vaccines in all age groups is important, particularly as new vaccines are introduced.
While a 38% effectiveness in those over 65 is disappointing, it is not unexpected. We’ve known for some time that as we get older, our immune response from the flu vaccine declines.
A couple of earlier blogs on this topic include:
Which is not to say that they have no value, only that those over 65 – who are normally at greatest risk from influenza – may get less protection than do younger adults from the shot.
Last year, NFID - the National Foundation for Infectious Diseases - convened a group of experts to address the issues of influenza and the elderly. From that panel a 5-page brief has emerged, called: Understanding the Challenges and Opportunities in Protecting Older Adults from Influenza.
While the elderly generally see less protection from the flu vaccine, they state that older individuals may still mount a robust immune response. In populations 65 and older, the brief points out that:
- Hospitalization rates for influenza and pneumonia are lower in community-dwelling adults who received the seasonal influenza vaccine.
- Immunization is associated with reduced hospitalization of older patients for cardiac, respiratory, and cerebrovascular diseases.
While the goal of vaccinating the younger population is to prevent infection, the authors point out that:
. . . the goal in older adults is to prevent severe illness, including exacerbation of underlying conditions, hospitalization, and mortality.
In other words, even if the vaccine doesn’t always prevent infection in the elderly, studies suggest that the vaccine may blunt the seriousness of the illness in those over 65.
The authors also point out that new vaccine technologies are being tested including the new high-dose influenza vaccine (see MMWR On High Dose Flu Vaccine For Seniors, Vaccines: Sometimes You Just Need A Bigger Hammer), Intradermally administered flu vaccines, and in Europe, the inclusion of adjuvants.
While everyone wishes the flu vaccine were 100% effective for 100% of the population, the bottom line remains:
Influenza is not a trivial illness, and causes much sickness and death every year.
While not 100% effective, the flu vaccine has an excellent safety record and can significantly reduce your odds of catching the flu.
So despite lackluster VE ratings, I’ll be rolling up my sleeve again this year. And so should you.