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The recommendation by the CDC for young children receiving the (unadjuvanted) flu vaccine is that:
Children less than nine years of age being vaccinated for the first time should receive two doses of influenza vaccine, spaced at least 4 weeks apart in the initial year.
The assumption has also been that during a pandemic, even previously immunized children would require 2-doses of vaccine against any emerging novel virus.
A 1-dose vaccination schedule would be highly desirable, provide savings in both time-to-immunity and resources.
We’ve a study that appeared yesterday in the journal Pediatrics that looks at the effectiveness of a single adjuvanted flu shot given to children during the fall of 2009 for the H1N1 pandemic (my thanks to loyal reader Anne who forwarded this link to me).
What they found was that a single dose of the AS03-adjuvanted vaccine conferred significant protection against influenza-related hospitalization in children aged 6 months to 9 years of age.
Effectiveness of Pandemic H1N1 Vaccine Against Influenza-Related Hospitalization in Children
Rodica Gilca, MD, PhDGeneviève Deceuninck, MD, MSc, Gaston De Serres, MD, PhD, Nicole Boulianne, MSc, Chantal Sauvageau, MD, MSc, FRCPC, Caroline Quach, MD, MSc, FRCPC, François D. Boucher, MD, FRCPC, Danuta M. Skowronski, MD, MHSc
Abstract
<SNIP>
Results: The overall effectiveness of a single pediatric dose of vaccine administered ≥14 days before illness onset was 85% (95% confidence interval [CI]: 61% to 94%), varying according to age category but with wide and overlapping CIs: 92% (95% CI: 51% to 99%) in 6–23 month-old children, 89% (95% CI: 34% to 98%) in 2–4 year-olds, and 79% (95% CI: −31% to 96%) in 5–9 year-olds. Overall vaccine effectiveness for immunization ≥10 days before illness onset was slightly lower at 80% (95% CI: 60% to 90%), with similar variation according to age.
Conclusion: In children aged 6 months to 9 years, a single pediatric dose of the AS03-adjuvanted pH1N1 vaccine was highly protective against hospitalization beginning at 10 and 14 days after vaccination.
Adjuvants such as AS03 are additives that are used to increase the immune response to a vaccine. While they have been used in Europe and in Canada, adjuvanted flu vaccines have not been licensed for use in the United States.
With tens of millions of adjuvanted flu vaccines deployed since the pandemic of 2009, we are getting more data on their impact.
In February of this year, in BMJ: Effectiveness of AS03 adjuvanted pandemic H1N1 vaccine researchers found the vaccine to be 93% effective, at least in recipients under the age of 50.
In December of 2010, in Lancet: Immunogenicity and safety Of Adjuvanted Flu Vaccines, researchers compared the safety and immunogenicity of GSK’s adjuvanted (AS03A) H1N1 pandemic vaccine and Baxter’s non-adjuvanted 2-Dose pandemic vaccine.
They found the adjuvanted split-virus vaccine achieved a stronger and faster immune response than the whole-virus non-adjuvanted vaccine.
They also found that a single antigen-dose sparing adjuvanted vaccination mounted a sufficient immune response in adults and adolescents, although the elderly might require a second shot.
Safety of the two vaccines was comparable, although recipients of the adjuvanted vaccine were more likely to report injection site soreness, and general complaints (malaise, fever, headaches) than did those who received the non-adjuvanted vaccine.
And in May of 2010 we saw a comparison study (see BMJ: Immunogenicity Of Adjuvanted vs. Unadjuvanted H1N1 Vaccines) between GSK’s Pandemrix, containing the adjuvant AS03, verses Baxter’s unadjuvanted Celvapan in British children.
Although the adjuvanted Pandemrix vaccine was associated with a higher rate of (usually mild) side effects (fever, injection site soreness), it produced a superior immune response.
One unresolved question regarding the safety of adjuvants stems from the increase in narcolepsy seen among recipients of the 2009 Pandemrix vaccine in Finland (see Finland: Task Force Report On Pandemrix-Narcolepsy Link).
This report found:
In approximately one quarter of those who developed narcolepsy following Pandemrix vaccination, the THL Immunology laboratory found antibodies binding to the AS03 adjuvant component of the vaccine.
Adjuvants containing squalene have not previously been reported to induce the production of antibodies. The significance of this preliminary observation will be the subject of further research.
Whether these antibodies are in any way connected to these rare cases of narcolepsy – or in any way affects the health of the vaccine recipients – has yet to be determined.
Complicating matters, more than a dozen countries reported an increase in narcolepsy during the 2009 pandemic, even those where the adjuvanted vaccine was not used.
You can find details on one such study in Stanford Study Finds Influenza – Narcolepsy Connection that linked narcolepsy not to the vaccine . . . but to the influenza virus itself.
Even if the adjuvant is eventually linked to these cases (and the jury on that is still out), Finland’s Narcolepsy taskforce found that the use of the vaccine probably saved lives and that `overall benefit-risk balance remains positive.’
Despite a few nagging questions over the safety of adjuvants in some quarters, studies over the past couple of years continue to reassure in terms of both safety and efficacy.
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