# 5230
Three days ago (see PLoS Medicine: Effectiveness Of The 2009 Pandemic Vaccine) we saw a study that strongly indicated that the 2009 pandemic H1N1 vaccine was highly effective in preventing infection by that virus.
Today, another study, this time conducted in the UK and appearing in the Eurosurveillance Journal, that comes up with nearly identical results; an adjusted vaccine effectiveness for adults under 65 of about 72%.
The short version of what this new study found was:
Out of 5,985 individuals whose samples were collected and PCR tested during the surveillance period, two samples were positive for influenza B and one sample was positive for influenza A(H3): these three cases were excluded from the study.
Of the remaining 5982 samples, 1,746 (29.2%) tested positive for pandemic A(H1N1) virus, while the remainder either tested positive for another respiratory virus, or their infections went unidentified.
Among those who had received the pandemic vaccine, only four of 85 (4.7%) were positive for the H1n1 virus 14 or more days after immunization, while 870 (28.4%) of 3,067 unvaccinated individuals had contracted the virus.
The authors list a number of potential limitations to their study, including a lack of data on the medical history of each case sampled, the fact that one manufacturer’s vaccine (GSK) dominated in this study, the use of convenience samples rather than random sampling from patients, and the low number of pediatric cases who had accepted the vaccine.
Still, the authors conclude:
. . . this study provides evidence that the pandemic influenza A(H1N1)2009 vaccine provided good protection against infection with pandemic influenza A(H1N1)2009 seven days or more after vaccination during the pandemic period.
Further work is required to ascertain the effectiveness of the pandemic vaccine in children, in specific clinical risk groups and by individual vaccine brand.
You can read the entire research in the latest edition of Eurosurveillance. I’ve reproduced the link and abstract below.
Hardelid P, Fleming DM, McMenamin J, Andrews N, Robertson C, SebastianPillai P, Ellis J, Carman W, Wreghitt T, Watson JM, Pebody RG.
Euro Surveill. 2011;16(2):pii=19763. Avail.online: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19763
Following the global spread of pandemic influenza A(H1N1)2009, several pandemic vaccines have been rapidly developed. The United Kingdom and many other countries in the northern hemisphere implemented seasonal and pandemic influenza vaccine programmes in October 2009. We present the results of a case–control study to estimate effectiveness of such vaccines in preventing confirmed pandemic influenza infection.
Some 5,982 individuals with influenza-like illness seen in general practices between November 2009 and January 2010 were enrolled. Those testing positive on PCR for pandemic influenza were assigned as cases and those testing negative as controls. Vaccine effectiveness was estimated as the relative reduction in odds of confirmed infection between vaccinated and unvaccinated individuals. Fourteen or more days after immunisation with the pandemic vaccine, adjusted vaccine effectiveness (VE) was 72% (95% confidence interval (CI): 21% to 90%).
If protection was assumed to start after seven or more days, the adjusted VE was 71% (95% CI: 37% to 87%). Pandemic influenza vaccine was highly effective in preventing confirmed infection with pandemic influenza A(H1N1)2009 from one week after vaccination. No evidence of effectiveness against pandemic influenza A(H1N1)2009 was found for the 2009/10 trivalent seasonal influenza vaccine (adjusted VE of -30% (95% CI: -89% to 11%)).
The perennial rap against flu vaccines by their critics is A) they don’t work and B) they are unsafe.
Study after study have shown that these two allegations are false.
Surveillance and reporting systems have not found any unusual pattern of deaths in the United States attributable to the pandemic vaccine, and the oft predicted spike in Guillain-Barré syndrome (GBS) never occurred (see CIDRAP VAERS study finds H1N1 vaccine safety similar to seasonal vaccines').
Flu vaccines in general, and the pandemic vaccine in particular, have a track record of being both very safe and effective.
Granted, NOT 100% safe, and NOT 100% effective.
Because nothing ever is.
But given the morbidity and mortality attached to the flu, I’ll take the shot over that any year.
