Shield Against Avian Influenza Pandemic?

TOPLINE:

In this prospective observational study, immune protection against H5N1 and H7N9 avian influenza virus (AIV) was almost absent prior to vaccination. However, seasonal influenza vaccines induced a seroprotective response against the H5N1 subtype in nearly 15% of younger individuals.

METHODOLOGY:

• Researchers conducted a prospective study to evaluate baseline levels of protection and the presence of neutralizing antibodies against the AIV subtypes H5N1 and H7N9 in different adult age groups.
• They included a total of 135 adults who were vaccinated with inactivated influenza vaccine (IIV) during the 2021-2022 influenza season and categorized them into those born between:
  • 1925-1967 (group 1 [G1]; n = 41; mean age, 79.4 years); likely primed by A(H1N1) and A(H2N2) clade 1 viruses.
  • 1968-1977 (group 2 [G2]; n = 49; mean age, 48.4 years); likely primed by A(H3N2) subtype clade 2 virus.
  • 1978-1997 (group 3 [G3]; n = 40; mean age, 35.1 years), likely primed by A(H3N2) and A(H1N1) reemergent viruses.
• A serum sample was obtained at three timepoints from each vaccinated individual: Before vaccination with seasonal IIV, 1 month after vaccination, and 6 months after vaccination.
• Immunological assays such as hemagglutination inhibition and viral neutralization were performed to evaluate immune responses in different age groups at various timepoints of vaccination.
• Cross-protection triggered by IIV was studied using engineered recombinant viruses expressing hemagglutinin and neuraminidase antigenic proteins of the H5N1 and H7N9 strains tagged with reporter genes.

TAKEAWAY:

• Only 2.4% of individuals in G1 had protective antibodies against H5N1 before vaccination, while antibodies against H7N9 were absent across all vaccinated groups.
• One month after seasonal vaccination, H5N1 antibody response was greatest in G3 (15%), followed by G2 (12.2%), though responses to H7N9 were minimal. After 6 months, seroprotection against AIV remained 2% or lower in all cases.
• One month after seasonal vaccination, individuals in G2 and G3 exhibited increased levels of cross-protective neutralizing antibodies against H5N1 (31.4% and 39.5%, respectively) and H7N9 (35.3% and 51.2%, respectively).

IN PRACTICE:

“The results of our study indicate that probably the best vaccination strategy during the early stages of an AIV [avian influenza virus] pandemic will likely involve immunization first with seasonal IIV [inactivated influenza vaccine], followed, when it becomes available, with an AlV-specific vaccine or with specific newly designed H5N1 vaccines. This would lead to a more robust seroprotection compared with the single administration of the monovalent H5N1 vaccine,” the authors wrote.

SOURCE:

The study was led by Iván Sanz-Muñoz, National Influenza Centre, Hospital Clinico Universitario de Valladolid, Valladolid, Spain. It was published online on December 31, 2024, in mBio.

LIMITATIONS:

The study used traditional measures of protection to evaluate neutralization and failed to observe the seasonal vaccine effect in children.

DISCLOSURES:

The study was supported by the National Institute of Allergy and Infectious Diseases, National Institutes of Health, Department of Health and Human Services, and others. The authors declared no conflicts of interest.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.