A new, surface-antigen-adsorbed influenza virus vaccine. I. Studies on immunogenicity in hamsters

Animal Models Utilized for the Development of Influenza Virus Vaccines

Animal models have been an important tool for the development of influenza virus vaccines since the 1940s. Over the past 80 years, influenza virus vaccines have evolved into more complex formulations, including trivalent and quadrivalent inactivated vaccines, live-attenuated vaccines, and subunit vaccines. However, annual effectiveness data shows that current vaccines have varying levels of protection that range between 40–60% and must be reformulated every few years to combat antigenic drift. To address these issues, novel influenza virus vaccines are currently in development. These vaccines rely heavily on animal models to determine efficacy and immunogenicity. In this review, we describe seasonal and novel influenza virus vaccines and highlight important animal models used to develop them.

Free haemagglutinin in inactivated whole virus influenza vaccines

While studying the haemagglutinin content of whole virus inactivated influenza vaccines by the single radial diffusion test and quantitative electron microscopy, it was found that not all haemagglutinin measured by single radial diffusion was bound to virions, a part of it being in a free state. The influence of unbound haemagglutinin on the immunogenicity of whole virus inactivated influenza vaccine is discussed. In addition, the use of single radial diffusion for the assessment of unbound haemagglutinin is suggested.

Production of passive immunity in neonatal ferrets following maternal vaccination with killed influenza A virus vaccines

Neonatal ferrets may be passively immunized following maternal vaccination with formalin-inactivated influenza A virus vaccine, but the level of protection from partial to complete depends upon the number of doses used to vaccinate the mother, the presence or absence of aluminum hydroxide adjuvant, whether or not the mothers were 'primed' by prior infection with a serologically heterologous type A virus, and the age of the neonate at challenge. Neonates were completely protected up to 2 weeks of age, but susceptibility returned to nasal epithelium at 5 weeks and to lung at 7 weeks. Mothers immunized up to 9 months previously also partially or completely protected their offspring, this correlating with the maternal serum haemagglutination-inhibition (HI) antibody titre at the time of neonatal challenge, not the duration of immunity.

Responses of volunteers to inactivated influenza virus vaccines

Three different types of bivalent influenza virus vaccine, a whole virus, an aqueous-surface-antigen vaccine and an adsorbed-surface-antigen vaccine were tested at three dosage levels in volunteers primed with respect to only one of the haemagglutinin antigens present in the vaccines. The local and systemic reactions to all three vaccine types were mild in nature and, following first immunization, the aqueous-surface-antigen vaccine was the least reactogenic. The serum haemagglutination-inhibiting antibody response to the A/Victoria/75 component of the vaccines to which the volunteer population was primed, was greatest following immunization with the aqueous-surface-antigen vaccine; the greatest antibody response to the A/New Jersey/76 component of the vaccines was observed following immunization with whole virus vaccine.

A surface antigen influenza vaccine. 1. Purification of haemagglutinin and neuraminidase proteins

Influenza virus was centrifuged in a KII rotor through a sucrose gradient containing Triton N101, a non-ionic surfactant. The micelles of surfactant formed a band in the gradient. As virus particles passed through the surfactant, the haemagglutinin and neuraminidase proteins were stripped from the surface and remained near the surfactant micelles. The residual virus particles sedimented into a denser region of the gradient and were thus separated from the haemagglutinin and neuraminidase antigens. Fractions containing the surface antigens were pooled and Triton was removed by phase-separation at the cloud point.

A surface antigen influenza vaccine. 2. Pyrogenicity and antigenicity

Conventional influenza vaccine containing whole virus particles purified on a zonal centrifuge is pyrogenic and can cause systemic and local adverse side effects. An improved vaccine was therefore prepared which contained only the surface antigens of the virus adsorbed to aluminium hydroxide. The antigenicity of this vaccine was compared with conventional vaccine in chickens. Both vaccines induced similar titres of serum haemagglutination-inhibition and neuraminidase inhibition antibody. The dose response curves, however, were different. The surface antigens at vaccine strength without aluminium hydroxide were of negligible pyrogenicity in rabbits.

A new surface-antigen-adsorbed influenza virus vaccine. II. Studies in a volunteer group

A group of 23 volunteers were each inoculated with 600 CCA of a new form of influenza virus A/England/42/72 vaccine; this vaccine consisted of purified haemagglutinin and neuraminidase antigens adsorbed to alhydrogel. No significant reactions to the vaccine were reported. Twenty-two volunteers produced increased titres of serum HI antibody, and all showed increased titres of NI antibody after immunization. Thus, for volunteers with no pre-immunization serum HI antibody, the geometric mean titre of serum antibody increased from 1/5 to 1/196 after immunization. Ten volunteers developed local neutralizing antibody after immunization; this antibody response was detected most frequently in volunteers who showed the greater serum antibody response to immunization, and in nasal washings with the higher concentrations of protein and IgA. Ten weeks after immunization, the vaccinees and a group of matched controls were inoculated intranasally with attenuated A/England/42/72 virus. Evidence of infection with the challenge virus was found in 14 of the control subjects and in one of the vaccinees. The results indicate that the surface-antigen-adsorbed vaccine induced high titres of serum antibody, and gave significant protection against challenge infection.