Immunization of man and animals against influenza by oral and intranasal routes.

The research paper demonstrates that human and equine influenza viruses can be weakened through serial passages on a specific system and then administered as live vaccines either through oral or intranasal methods. The study finds that these vaccines effectively trigger an immune response in both humans and horses, though there is a variance in response based on the number of virus passaging and the mode of vaccination.

Experimental Approach

• The researchers used live strains of the human and equine influenza virus, which were made weaker by a method called ‘serial passaging’, conducted on an ‘allantois-on-shell’ (AOS) system. This system is often used for cultivating and propagating viruses.
• These weakened viruses were then administered to human volunteers and horses either orally or intranasally.

Observations in Humans

• When the virus strains modified by five or fewer passages on the AOS system were administered to volunteers, a range of responses was observed. These included mainly mild clinical reactions, the replication of the virus in the nasal mucosa, transmission to those given a placebo, and a significant increase in local or circulating antibodies.
• When the virus strains had undergone up to ten passages on AOS, the reactions were milder, with no replication or viral transmission observed. The immunogenicity, or ability to provoke an immune response, was also lower.

Observations in Horses

• In horses and young horses (colts), the researchers observed similar response patterns as in humans. However, the A/Eq-2 strain of the virus was heavily shed following the challenge in placebo recipients.
• Colts that were vaccinated intranasally were completely protected, while about one third of colts vaccinated orally shed small quantities of the A/Eq-1 and A/Eq-2 viruses. Despite this, there was a swift and significant increase in local antibodies against both strains measured two days after the immunization challenge in all three groups (intranasally immunised, orally immunised, and Placebo).