1
There's one vaccine composition for the southern hemisphere and one for the northern hemisphere each year.
The WHO publishes the composition recommendations.
For example, the composition for the 2019/2020 northern hemisphere winter season was:
an A/Brisbane/02/2018 (H1N1)pdm09-like virus;
an A/Kansas/14/2017 (H3N2)-like virus;
a B/Colorado/06/2017-like ...
1
https://www.polleninfo.org/fileadmin/template/img/chartimages/currency/resized/POAC_06_1.gif
According to the little number on the lower left, this is from 2012. The situation is worse than I expected in Europe. Also, there is a map from the states:
http://www.allamericanallergy.com/images/Ragweed%20Pollen%20Map%2008-25-2014.jpg
It will be so cool to ...
Only top voted, non community-wiki answers of a minimum length are eligible