Efficacy of Avian influenza vaccines, H5 subtype

Summary of data

Introduction

Since 2002, Hong Kong has vaccinated successfully against H5N1 outbreaks with an inactivated H5N2 vaccine (Nobilis Influenza H5, Intervet). After the start of new outbreaks of Avian Influenza, sub-type H5N1, in Asia in 2003, it was questioned whether the present H5N2 vaccines offered protection against the 2003 H5N1 field isolate.

In this study 2 H5N2 vaccines (Nobilis Influenza H5, origin Mexico and Nobilis H5N2, origin Spain, both vaccines are from Intervet) were tested in a challenge experiment.

The study was carried out by Dr. David E. Swayne, DVM, PhD, Laboratory Director Southeast Poultry Research Laboratory, USDA/ARS, Athens, Georgia.

This summary is made by Intervet and based on the experimental data, received from Southeast Poultry Research Laboratory. The results of this study will be submitted for publication in a peer-reviewed scientific journal later in 2004.

Materials

Vaccines

Inactivated vaccines, adjuvant water in oil emulsion.

Nobilis Influenza H5N2, origin Mexico, produced by Intervet.
Nobilis Influenza H5N2, origin Spain, produced by Intervet.

Test animals

SPF White Leghorn chickens, age at vaccination 3 weeks of age.

Challenge

Intranasal challenge with 10^6.0EID₅₀ at 3 weeks post vaccination (H5N1 isolate from the AI outbreak in Asia in 2003).

Groups

Group 1: No vaccination against AI, vaccination against ND.
Group 2: Nobilis Influenza H5, batch MM 03424, expiry 12/2005 (500ml, 1000 dose), 0.5 ml per dose, administration subcutaneous.
Group 3: Nobilis Influenza H5N2, batch IP 0305036, expiry 12/2004 (100ml, 200 dose), 0.5 ml per dose, administration subcutaneous.

Results

Morbidity:
- In the control group (Group 1) all chickens showed clinical signs of high pathogenic Avian Influenza virus infection.
- In vaccinate Group 2, none of the chickens showed clinical signs.
- In vaccinate Group 3, only 1 chicken showed clinical disease. This chicken did not have a pre-challenge antibody titre, which might indicate that it was a non-responder or possibly was missed during vaccination.
Mortality:
- In the control group (Group 1) all chickens died of Avian Influenza.
- In vaccinate Group 2 none of the chickens died.
- In vaccinate Group 3 only 1 chicken died. This chicken did not have a pre-challenge antibody titre, which might indicate that it was a non-responder or possibly was missed during vaccination.
Serology:
- None of the chickens in the control group (non-vaccinated against AI, Group 1) had pre-challenge antibody titres in the AGP and HI test.
- In vaccinate Group 2 all chickens had pre-challenge titres in the AGP and in the HI test (average 1:128).
- In vaccinate Group 3, 9 out of 10 chickens had pre-challenge titres in the AGP and in the HI test (average 1:120).
Re-isolation of challenge virus on day 2 post-challenge:
- In the control group (Group 1) all chickens (10 of 10)excreted the challenge virus The average virus titre was 10^6.16EID₅₀ /ml in oropharyngeal swab media and 10^5.82EID₅₀ /ml in cloacal swab media.
- In vaccinate Group 2, 5 out of 10 chickens excreted virus from the oropharynx with an average titre of 10^1.23EID₅₀ /ml of oropharyngeal swab media and 3 of 10 chickens excreted virus from cloaca with an average titer of 10^1.0EID₅₀ /ml of cloacal swab media.
- In vaccinate Group 3, 6 out of 10 chickens excreted virus from the oropharynx with an average titre of 10^1.78EID₅₀ /ml of oropharyngeal swab media and 3 of 10 chickens excreted virus from cloaca with an average titre of 10^1.53EID₅₀ /ml of cloacal swab media.

Summary of re-isolation rates.

Virus isolation (2 DPC) log₁₀EID₅₀ titre per ml
	oral		cloacal
	Animals excreting	Average in excreting birds	Animals excreting	Average in excreting birds
Group 1, controls	10/10	6.16	10/10	5.82
Group 2, vaccinated	5/10	1.23	3/10	1.00
Group 3, vaccinated	6/10	1.78	3/10	1.53

Conclusions

The experiment showed that both vaccines induced complete protection against clinical disease and mortality with the exception of 1 bird in Group 3, which did not have pre-challenge antibody titres.

The experiment showed that after challenge of non-vaccinated birds all birds excreted virus at 2 days after challenge at very high virus titres.

After challenge of vaccinated birds virus excretion was prevented in the majority of birds. In the birds, which excreted virus, the average virus titres were between 10.000 and 100.000 times less than in the non-vaccinated birds.

In an outbreak of Avian Influenza, reduction of virus circulation is a very important factor in preventing spread of Avian Influenza to other birds and to people. Reduction of virus excretion significantly reduces the chance that an infected farm will infect another farm.

This experiment shows that vaccination with the tested vaccines can have an important contribution to the control of Avian Influenza outbreaks.

Efficacy of Avian Influenza vaccines, H5 subtype (print version) (39Kb)
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