Raúl Ortiz de Lejarazu y Leonardo
Professor of Microbiology, scientific advisor and director emeritus of the National Influenza Centre in Valladolid
It is a study of very high quality, well conceived for the proposed objectives and impeccably carried out. The signatories are people of proven experience in this field, with numerous publications. I know some of these scientists personally.
It is a continuation of previous work. It is known that current influenza vaccines only protect against that year's influenza strains, with antibody evanescence after six months. HA (haemagglutinin) is the key component of influenza vaccines (like glycoprotein S in SARS-CoV-2 vaccines) and has two regions: one that varies a lot (the head) and one that varies little (more conserved), which is the stem. There are 16 different types of HA (plus two in bats that are not relevant) that are associated with two types of stems, 1 and 2. In this work they have tested the protein of stem 1, which serves for cross-protection against H1, H2 and H5 (although within the phylogenetic group 1 of the stem there are also 9, 11, 12, 13 and 16).
It has been manufactured on a platform with nanoparticles that allow better vehicleisation of the antigen and the results are very encouraging.
There are always limitations. Theoretically there are more types that have not been tested, but they are very rare and only present in wild birds. The duration of the antibodies seems good, over a year, so it meets the 2017 WHO targets.
In influenza, antibody measurements have been an accepted correlate of protection for over 50 years. It's not perfect, but it's pretty close. On that side of the article, there is nothing to doubt.