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Representative variants of H7N9 AIVs from Guangdong Province, China. (A) Alignment of the HA cleavage site from the five waves of H7N9 infection. Position numbers are shown according to the sequence of the highly pathogenic H7N9 variant A/Chicken/Heyuan/16876/2016. Wave numbers are marked wave I to wave V. (B) Frequency of isolation of H7N9 viruses from chickens and ducks recovered from 2013 to 2017 in Guangdong Province. The time ranges of the five waves are shown.
