Are flu vaccines different around the world? In sense - are they made to work against the same strain of viruses?
Or, perhaps - each region (i.e. Europe, Asia) expects a different virus strain and someone vaccinated against flu in Asia will not have much protection from that vaccine after traveling to Europe?
I think flu vaccines differ by hemisphere with different strains circulating in the north and south hemispheres. The World Health Organization makes recommendations. I assume there could be some difference based on different manufacturers but that generally speaking we get the same vaccine depending on which hemisphere we live in. I could be wrong.
Lol. In thinking about it, I should put "I could be wrong" in my signature block for everything I write. It kind of goes without saying. I thought covid would ease up in the summer. Duh me.
Per the CDC "seasonal flu vaccine protects against the influenza viruses that research indicates will be most common during the upcoming season." and yes the southern and northern hemisphere versions generally differ for that reason. The flu virus coat for a given strain changes over time, which is why even healthy immune systems may not identify a new infection from a strain we have seen before, either from an actual flu infection, or a vaccination.
Trivalent vaccines provide protection against the three most common anticipated strains and quadrivalent vaccines against the four most common anticipated strains.
Neil
The WHO makes some general recommendations.
who.int/influenza/vaccines/...
In addition to the observation that there are northern and southern hemispherical differences, each country decides which vaccines to give.
Equatorial countries have unique problems and traditions in this regard. I suspect that such countries that get more tourism from one hemisphere or the other lean accordingly.
Influenza Vaccine in Tropics and Subtropics
who.int/influenza/vaccines/...
Which vaccine formulation to use – Northern or Southern Hemisphere?
who.int/influenza/vaccines/...
A nice map from 2016 shows how countries have chosen in the past:
who.int/influenza/vaccines/...
=seymour=
California friends did a tour in Thailand, after getting all recommended shots here before going, including flu. They both ended up with very bad cases of flu - a different strain from what is covered by the vaccine given in the US, but would have been included had they gotten the vaccine there.
I’ve been reading Bill Bryson’s book ‘The Body’. Here’s a summary of what he says about vaccines, but based on some of the other comments here I don’t know whether he’s totally correct …
“Every February the WHO & CDC get together and decide what to make the next flu vaccine from, usually based on what’s going on in Eastern Asia.
Based on all available information the WHO & CDC announce their (northern hemisphere) decision on 28 February and all the vaccine makers in the world begin working on the same strain
.
Says Kinch (from Yale) ‘From February to October they make the new vaccine in the hope that we will be ready for the next big flu season. But when a really devastating new flu emerges, there’s no guarantee that we will have actually targeted the right virus. In the event of a really catastrophic outbreak we wouldn’t be able to produce vaccine fast enough to inoculate everyone, even if the vaccine was effective’.”
But separately I read a CDC web page saying “WHO recommends specific vaccine viruses for inclusion in influenza vaccines, but then each country makes their own decision about which viruses should be included in influenza vaccines licensed in their country”.
cdc.gov/flu/prevent/vaccine....
Hope this helps,
BSMI
It gets cold in "tropical countries" - example Brazil : South of Rio-Sao Paulo it "gets cold" in the winter in the State of Santa Catarina similar to Florida (which gets a couple "cold" weeks), One community in the mountains, Sao Joaquim, get reliably snow every southern winter. Further south in Brazil, in Rio Grande do Sul state, people wear coats in the winter and communities in the "mountains" like Gramado get some snow and some fog, just enough to maintain a "Winter in the Alps" tourism, with hot cacao . Yes - people get flu inoculation in Jan.Feb. each year!
Flu shots
Flu and pneumonia vaccines
FLU VACCINE 
A Comparison of between Covid-19, a Cold, the Flu, Hay Fever and Asthma plus other Coronavirus updates
