Vaccine manufacturing countries
According to the WHO, as of 2019, countries where influenza vaccine is produced include:

In addition, Kazakhstan, Serbia and Thailand had facilities in final stages of establishing production. Cost-effectiveness
The cost-effectiveness of seasonal influenza vaccination has been widely evaluated for different groups and in different settings. In the elderly (over 65), the majority of published studies have found that vaccination is cost saving, with the cost savings associated with influenza vaccination (e.g. prevented health care visits) outweighing the cost of vaccination. In older adults (aged 50–64 years), several published studies have found that influenza vaccination is likely to be cost-effective, however the results of these studies were often found to be dependent on key assumptions used in the economic evaluations. The uncertainty in influenza cost-effectiveness models can partially be explained by the complexities involved in estimating the disease burden, as well as the seasonal variability in the circulating strains and the match of the vaccine. In healthy working adults (aged 18–49 years), a 2012 review found that vaccination was generally not cost-saving, with the suitability for funding being dependent on the willingness to pay to obtain the associated health benefits. In children, the majority of studies have found that influenza vaccination was cost-effective, however many of the studies included (indirect) productivity gains, which may not be given the same weight in all settings.
As of November 2007, both the conventional injection and the nasal spray are manufactured using chicken eggs. The European Union also approved Optaflu, a vaccine produced by Novartis using vats of animal cells. This technique is expected to be more scalable and avoid problems with eggs, such as allergic reactions and incompatibility with strains that affect avians like chickens.Influenza vaccines are produced in pathogen-free eggs that are eleven or twelve days old. The top of the egg is disinfected by wiping it with alcohol and then the egg is candled to identify a non-veinous area in the allantoic cavity where a small hole is poked to serve as a pressure release. A second hole is made at the top of the egg, where the influenza virus is injected in the allantoic cavity, past the chorioallantoic membrane. The two holes are then sealed with melted paraffin and the inoculated eggs are incubated for 48 hours at 37 degrees Celsius. During incubation time, the virus replicates and newly replicated viruses are released into the allantoic fluidAfter the 48-hour incubation period, the top of the egg is cracked and the ten milliliters of allantoic fluid is removed, from which about fifteen micrograms of the flu vaccine can be obtained. At this point, the viruses have been weakened or killed and the viral antigen is purified and placed inside vials, syringes, or nasal sprayers. Done on a large-scale, this method is used to produce the flu vaccine for the human population.