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Partial Anthrax Vaccination Stimulates Significant Antibody Response

By Eric Toner, M.D., January 26, 2007

In an article to be published in the February 19, 2007 issue of the journal Vaccine and made available online in advance of publication, Lininger and colleagues report on their study of serum anti-protective antigen (PA) concentrations in marines who had been previously vaccinated with the FDA-licensed Anthrax Vaccine Absorbed (AVA). They found that those who had not completed a full vaccination series of 6 injections still had a significant antibody response and that 6 doses provided no significant advantage over 4 doses.

In early 2000 the military suspended its Anthrax Vaccine Immunization Program, providing an opportunity to assess the efficacy of partial anthrax vaccination. The investigators looked retrospectively at volunteers from the Third Marine Expeditionary Force stationed in Okinawa. Of 363 subjects, almost all of whom were healthy young men, 44 had received the full standard series of 6 AVA doses (0, 2, 4 weeks and then 6, 12, 18 months), 111 had received no vaccination, and the remaining 208 received an incomplete vaccination series varying between 1 and 5 doses. Blood was drawn on average 30 months after the last vaccination (range 3-57 months) and tested for the serum concentration of anti-PA specific IgG using a quantitative ELISA procedure. The CDC’s reactive threshold of 3µg/ml was used to define a positive antibody response to vaccination.

Results

The investigators report the following:

  1. Most of the subjects who received at least one vaccination had a positive antibody response.

  2. The percentage with a positive response increased from 55% to 90% as the number of doses received increased from 1 to 4.

  3. The serum concentration of anti-PA IgG increased linearly as the number of doses increased from 1 to 4.

  4. There was a marked increase in anti-PA IgG concentration as the number of doses received increased from 3 to 4.

  5. There was no significant difference in anti-PA IgG concentration in those who received 4, 5 or 6 doses.

Conclusions

Based upon the serum concentrations of anti-PA antibodies produced, this study suggests that the current regimen of 6 doses of AVA may be more than is required to achieve maximal humoral immunity to the PA of B. anthracis toxin. Further study will be needed to assess whether the immunity generated by an abbreviated course is durable as compared with standard AVA course.

Reference

Lininger LA, Cullum ME, Lyles MB and Bienek DR. The impact of incomplete vaccination schedules on the magnitude and duration of protective antigen-specific IgG responses in recipients of the U.S. licensed anthrax vaccine. Vaccine:25;1619-1625 Available online at  http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TD4-4MBCHN1-3&_user=88470&_rdoc=1&_fmt=&_ orig=search&_sort=d&view=c&_acct=C000006998&_   version=1&_urlVersion=0&_userid=88470&md5=   ec49e53cbb5c15c3f2c33632fd97a0ee. Accessed January 24, 2007.

Note to readers:
The Infectious Diseases Society of America (IDSA) yesterday published a policy document entitled “Pandemic and Seasonal Influenza Principles for U.S. Action” which is available online at http://www.idsociety.org/Content/NavigationMenu/ News_Room1/Pandemic_and_Seasonal_Influenza/ IDSA_ flufinalAPPROVED1.24.07.pdf