The two main ones circulating this year are A(H1N1)pdm09 and B(H3N2)Victoria. A(H1N1)pdm09 is pretty similar to B(H1N1)Yamagata which was included in the shot last year and was mixed with the current updates, so it has tested well against the virus so far because of the similarities in their makeup. B(H3N2)Victoria on the other hand, is not testing well against the vaccine at all because only a small portion of the updates are similar to it. They're theorizing at the moment that the recent influx of Japanese tourists to the west coast in the last couple years caused the similarity between the current strain and the Yamagata strain, as the Japanese Yamagata flu probably at some point combined itself with an American flu from the extended close contact between tourists and locals in California/Oregon/Washington. The Victoria flu is from Australia, and is very different from pretty much any recent American flu, so our vaccines aren't really doing very well. Australia's vaccines also aren't really equipped to handle it because they put much more emphasis on the Brisbane flu instead of the Victoria flu this year. New and updated flu shots this year are supposed to be quadrivalent including these four strains: A/Brisbane/02/2018 (H1N1) A/Kansas/14/2017 (H3N2) B/Colorado/06/2017 (H1N1) B/Phuket/3073/2013 (H1N1) So basically one of them is covered and one of them not so much.