You didnt get my point @kabu. When I said that it depends on how fast the virus significantly changes, I meant exactly that the vaccine might no longer fit to the virus ( like in your flu example),thats true for every vaccine ever produced, its just that this case is not what your 9-10 months apply to. There’s a big difference if you assume the virus to change every 9 month or if vaccines effect is over. And regarding the latter, our bodys immune system naturally is consisting of more than just antibodies. Among that are memorizing t-cells that will stay in our blood for years. I’ve written about that in my last post and that thought is part of the publication I mentioned. These kind of t-cells are in principle no new knowledge, it just has not been the priority for the first wave of vaccines. And new vaccines planned will take more care of that. Your calculation isnt wrong, your assumtion about the validity of that timeframe in the long run will very likely be wrong. And in form of biontechs current vaccine it might even already be wrong.