For investigating the effectiveness of travel restrictions on COVID-19 transmission in China , we compared the population flow among 43 major cities ( including Wuhan ) during the same observation period in 2019 ( 12 January 2019 - 8 March 2019 ) and 2020 ( 1 January 2020 - 23 February 2020 ) . This data was extracted from Baidu Inc. ( Baidu Migration Map - Big data on Spring Migration ) . Fig . 3 showed the daily population inflow and outflow indexes of Wuhan and other top ten cities ( 4 first - tier cities , three transport hubs , and three developed coastal cities in southern and eastern China ) with highest average daily population inflow and outflow indexes . In Fig . 3 , the grey dotted line represented the day of Chinese Lunar New Year ( 6 February 2019 , 25 January 2020 ) . Because the spring migration was set according to the lunar calendar , we identified the observation periods in 2019 and 2020 according to the same lunar dates . Before the Chinese Lunar New Year , that was historically the peak period for spring migration with the increasing daily population outflow indexes of Wuhan and other top ten cities in 2019 and 2020 ( Fig . 3c ) . However , in 2020 , the average daily population outflow indexes of these cities were more than 1.1 times that in 2019 , especially in Wuhan ( 1.2 times ) . After the Chinese Lunar New Year , that was also historically the peak period for traveling and returning to work , with the increasing daily population inflow indexes of Wuhan and other top ten cities just in 2019 . Travel restrictions and large - scale control measures were implemented in China from 23 January 2020 , which caused a rapidly decreasing daily population inflow and outflow indexes of these cities . During this period , the average daily population inflow and outflow indexes of these cities were 30 % of that in 2019 , especially in Wuhan ( only 9 % ) .