The situation is only somewhat better for surveillance efforts
based upon Twitter [77–92]. While a small portion of the realtime
message stream (1%, or 10% for certain grandfathered users)
is available outside the company at no cost, terms of use prohibit
sharing historical data needed for calibration between researchers.
Access rules are similar or significantly more restrictive for other
social media platforms such as Facebook and Sina Weibo, the
leading Chinese microblogging site (http://weibo.com). Consistent
with this, we were able to find no research meeting our inclusion
criteria based on either of these extremely popular systems.