Xiao B, Xu Z, Viennois E, et al
It's best to get treated for B12 deficiency anemia and avoid any long-term problems
Other groups who may benefit include: Patients following gastric surgery (gastrectomy, bariatric procedures) where intrinsic factor production or absorption sites are compromised Individuals with malabsorption disorders such as Crohn's disease, coeliac disease, or chronic pancreatitis Strict vegans and vegetarians with dietary insufficiency, though oral supplementation is usually tried first Elderly patients with atrophic gastritis or reduced gastric acid production Patients on long-term metformin or proton pump inhibitors, which can impair B12 absorption [6] [8] Individuals with nitrous oxide exposure (recreational or medical), which can cause functional B12 deficiency Diagnosis typically involves serum B12 measurement, with levels below approximately 148 pmol/L (though thresholds vary between laboratories) generally indicating deficiency

Internal proteins such as the polymerase subunits (PA, PB1, PB2), matrix and nucleoprotein can have conservation in sequence of 7797% within influenza A but much reduced conservation with influenza B species
But some may notice mild effects, especially with injections
This interval catches declining levels before symptoms develop