# 7807
The standard advice for getting the seasonal flu vaccine is to get it as soon as it becomes available in the fall, as explained in the following excerpt from the CDC’s Misconceptions about Seasonal Flu and Flu Vaccines (updated May 2013).
Should I wait to get vaccinated so that my immunity lasts through the end of the season?
No. CDC recommends that influenza vaccination begin as soon as flu vaccine becomes available and continues throughout the flu season. The flu season is unpredictable, and since it takes about two weeks after vaccination for antibodies to develop in the body that protect against influenza virus infection, it is best that people get vaccinated early so they are protected before influenza begins spreading in their community. While immunity can vary by person, previously published studies suggest that immunity lasts through a full flu season. Although adults 65 and older typically have a reduced immune response to flu vaccination compared with young healthy adults, their immune protection still extends through one flu season. In addition, a review of published studies concluded that no clear evidence exists that immunity declines more rapidly in the elderly. Note: The high-dose vaccine for people aged 65 and older is intended to create a stronger immune response in this age group.
Challenging this conventional wisdom is a new study that appears in BMC Infectious Diseases that finds – at least among those over the age of 65 – the protective effects of a flu shot begins to diminish rapidly after four months. This study, which was conducted in Spain, involved a relatively small group of subjects, and so its results must be interpreted with caution.
First a link to the open access study, followed by a link to a CIDRAP NEWS article which nicely summarizes the results, after which I’ll return with more.
Effectiveness of influenza vaccine against laboratory-confirmed influenza, in the late 2011--2012 season in Spain, among population targeted for vaccination
Silvia Jiménez-Jorge, Salvador de Mateo, Concha Delgado-Sanz, Francisco Pozo, Inmaculada Casas, Manuel Garcia-Cenoz, Jesús Castilla, Esteban Pérez, Virtudes Gallardo, Carolina Rodriguez, Tomás Vega, Carmen Quiñones, Eva Martínez, Juana María Vanrell, Jaume Giménez, Daniel Castrillejo, María del Serrano, Julián Mauro Ramos and Amparo Larrauri
Abstract (provisional)
Background
In Spain, the influenza vaccine effectiveness (VE) was estimated in the last four seasons using the observational study cycEVA conducted in the frame of the existing Spanish Influenza Sentinel Surveillance System. To estimate influenza vaccine effectiveness (VE) against medically attended, laboratory-confirmed influenza-like illness (ILI) among the target groups for vaccination in Spain in the 2011--2012 season. We also studied influenza VE in the early (weeks 52/2011-7/2012) and late (weeks 8-14/2012) phases of the epidemic and according to time since vaccination.
Methods
Medically attended patients with ILI were systematically swabbed to collect information on exposure, laboratory outcome and confounding factors. Patients belonging to target groups for vaccination and who were swabbed <8 days after symptom onset were included. Cases tested positive for influenza and controls tested negative for any influenza virus. To examine the effect of a late season, analyses were performed according to the phase of the season and according to the time between vaccination and symptoms onset.
Results
The overall adjusted influenza VE against A(H3N2) was 45% (95% CI, 0--69). The estimated influenza VE was 52% (95% CI, -3 to 78), 40% (95% CI, -40 to 74) and 22% (95% CI, -135 to 74) at 3.5 months, 3.5-4 months, and >4 months, respectively, since vaccination. A decrease in VE with time since vaccination was only observed in individuals aged >= 65 years. Regarding the phase of the season, decreasing point estimates were only observed in the early phase, whereas very low or null estimates were obtained in the late phase for the shortest time interval.
Conclusions
The 2011--2012 influenza vaccine showed a low-to-moderate protective effect against medically attended, laboratory-confirmed influenza in the target groups for vaccination, in a late season and with a limited match between the vaccine and circulating strains. The suggested decrease in influenza VE with time since vaccination was mostly observed in the elderly population. The decreasing protective effect of the vaccine in the late part of the season could be related to waning vaccine protection because no viral changes were identified throughout the season.
From CIDRAP NEWS.
Study: Flu vaccine effectiveness may drop within a few months
The effectiveness of the influenza vaccine dropped from 52% at 3.5 months after vaccination to 22% more than 4 months after vaccination during the 2011-12 season, according to a study out of Spain today in BMC Infectious Diseases whose power was limited by a small sample size.
Researchers analyzed data from 342 primary care patients across the country who had influenza-like illness and for whom vaccination status and timing were known. Of these, 226 had lab-confirmed flu and 116 served as test-negative controls.
<SNIP>
The waning immunity appeared to be entirely tied to immune response in elderly patients. The researchers found the adjusted VE dropped from 85% (95% CI, 18 to 97) for patients older than 65 who were vaccinated 3 months before symptom onset to a null estimate for those in that age-group who were vaccinated more than 4 months before symptom onset. The trend, however, was not statistically significant.
The team did not find decreased VE with time in patients younger than 65 years.
In the interest of full disclosure, I get the flu vaccine every year and I’ve already had mine earlier this month (see NPM13: Giving Preparedness A Shot In The Arm), yet I’m fully aware that flu vaccines are not a panacea against influenza.
As we’ve discussed often, flu vaccines – while considered very safe – most years only offer a moderate level of protection against influenza, and that their VE (vaccine effectiveness) can vary widely between flu shot recipients, and is often substantially reduced among those older than 65 or with immune problems.
As an example, in October of 2011, in CIDRAP: A Comprehensive Flu Vaccine Effectiveness Meta-Analysis, we saw a major review indicating the TIV (Trivalent Influenza Vaccine) - during 8 of 12 flu seasons (67%) – produced a combined efficacy of only 59% among healthy adults (aged 18–65 years).
They found the protective effects of the flu vaccine could vary considerably from one season to the next, as well as among different age groups (see Study: Flu Vaccines And The Elderly).
Still, given their safety record, and relative low cost, I consider them to be good insurance against what can sometimes be a serious illness – particularly as I’m getting older. As an added incentive, we recently saw a study - that while far from conclusive - suggesting that the Flu Vaccine May Reduce Heart Attack Risk.
There is no doubt there is a pressing need for better flu vaccines (see CIDRAP: The Need For `Game Changing’ Flu Vaccines) - but until they can be developed - the flu shots we have – when coupled with good `flu hygiene’ (washing hands, covering coughs, staying home when ill) remain the best preventative actions you can take against the flu.
