Studio dell'immunogenicità di due vaccini influenzali pre-pandemici "Vero-derived A/H5N1/Indonesia/05/2005" su una popolazione adulta.

The high risk for a possible future avian influenza pandemic is alarming the entire scientific world. There are two main reasons: first of all, in the last decades is emerged the great ability of avian influenza virus (AIV) to infect both domestic and wild birds, with the possibility to spread the infection around the world thanks their migratory flights; then, the growing number of AIV strains isolated in the last years, proving the genomic mutation skills of the virus, leading to the high risk to become capable to infect humans, generating a possible influenza pandemic. In the present work two different studies has been performed in parallel with the aim to evaluate the immunogenicity of a new Vero-cell derived A/H5N1/Indonesia/05/2005, pre-pandemic influenza vaccine, in a healthy adult population after intramuscolar (IM) and intradermal injection (ID). In both cases, the serum of every patient was evaluate at three time points: V1, before vaccination, V2, after 21 days (for intramuscolar vaccine) and 28 days (for intradermal vaccine) from the first vaccination and then, V3, after 43 days from the first immunization. After V2, the population received a second dose of vaccine.The intramuscolare vaccine has been evaluated through 5 different HA concentration per dose (5-10-15-30-60 µg/dose); the population composed by 180 healthy adults, has been divided into 5 different cohorts. In order to evaluate the immunogenicity of the intradermal vaccine, the population was composed by 60 healthy adults, vaccinated with 15 µg of HA/dose. While in the first study, for each cohort was evaluated the intensity of the immune response through three different serological assays (SRH, HI and MN), in the second one, the evaluation was performed through the SRH and HI assays; the only two methods recognised and recommed by EMA to evaluate the immunogenicity and efficacy of a new influenza vaccine The vaccines evaluated in the present study brings an important innovation derived by the use of Vero cells platform for the production of the virus, to replace the classical method based on embryonated hen eggs. Infact, in case of influenza pandemic, the use of eggs could have some disadavantages: the current method of viral production requires at least of 6-9 months and, in addition, the high patogenic avian influenza virus can’t be propagated efficiently in embryonated hen eggs, because they kill the embryones very quickly. For the IM vaccine, correlations between the three serological assays were performed in order to evaluate the difference in antibodies detection for each assay. This IM vaccine has been administered in 5 different HA/dose concentrations. From the results it is possible to state that only the vaccine with 60 µg HA/dose is able to fullfil all CHMP criteria for all the methods considered; infact, the vaccine with only 30 µg HA/dose is able to fullfil the three CHMP criteria only in HI assay. Another important aspect to consider is the number of doses to administer in order to elicit a proper immune response: infact from the results emerged that a second dose of vaccine is recommended to obtain a statistically significant antibody increase in all cohorts. The results obtained showed a good and positive level of correlation, confirming the hypotesis of this vaccine to be able to elicit a broader specrum of antibody. It is not very easy to correlate the results obtained with the three different assays because of they detect the presence of different Abs classes: SRH assay detects the IgG1 and IgG3 implicate in the complement fixation reaction and direct only against the HA1 subunit, the HI assay lets to detect all antibodies that bind the HA1, then the MN is able to relieve the functional antibodies involved in neutralization reaction and directed both against HA1 both HA2 domains. Is important to keep in mind that this vaccine does not contain any adjuvants, generally used in seasonal vaccine in order to increase the immune response in elderly and immunocompromised people. In this study the majority of population resulted completely naïve against the A/H5N1/Indonesia/05/2005. This could explain why the concentrations of HA/dose generally used in intramuscolar vaccines (10-15 µg HA/dose) are not able to elicit a good antibody response in the majority of subjects in the present study. So, it would be interesting to evaluate the efficacy of this IM with the addition of an adjuvant in the formulation in order to reduce the HA concentration per dose; this introduction could be useful for the process of vaccines production (less HA concentration for dose would let to have more doses of vaccine available). Then, analyzing the same vaccine but administered through the intradermal route, and containing 15 µg HA/dose, it emerged that this vaccine does not fullfil none of the CHMP criteria neither in SRH nor in HI. Even though the results do not exceed the cut-off, is possible to see a statistically significant increase in antibody titers in the serum of the patients between pre and post vaccination. A first advantage is called “Dose-Sparing Concept”, that is using the same HA concentration for dose (15 µg), the intradermal vaccine let to use the half volume to injection respect a intramuscolar dose; in this way, in case of pandemic, it will be available a number of intradermal doses equal to twice the number of intramuscolar doses. This concept was re-evaluated in 2009 during the A/H1N1 “swine” outbreak. Another important advantage of intradermal vaccine is the easier way of administration. Infact, nowadays, special devices with micro-needles are present on the market and they let a quick, easy, painless and without side effects (e.g. no fever) administration. In case of trained personnel (such as: physicians, nurses etc.) the intradermal injection can be made in self-administration. Considering all these advantages it is clear how the choice of a new intradermal vaccine, it could be the winning choice for an efficient vaccine production and administration in case of influenza pandemic.