Table 2. Strongly correlated search terms with the number of influenza cases in different lag periods.

Lag time	Search keywords
The same month	Flu, flu symptoms, influenza type A, flu virus, the symptoms of flu, influenza drugs, viral flu, flu therapy, type A flu virus
Lag one month	Spanish flu, new type of flu, how to treat swine flu
Lag two months	Prevent flu
Lag three months	Influenza vaccine, is it necessary to get vaccinated against the flu, H1N1 flu, side effects of flu vaccine