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 |