without any post-exertional malaise ("crashes"). APT states that persons should plan to increase their activity, as able. However, APT also requires patients to restrict their activity level to only 70% of what they feel able to do, while also warning against too much rest. This has been described as contradictory, and Jason states that in comparison with pacing, this 70% limit restricts the activities that patients are capable of and results in a lower level of functioning. Jason and Goudsmit, who first described pacing and the energy envelope theory for CFS, have both criticized APT for being inconsistent with the principles of pacing and highlighted significant differences. APT was promoted by Action for ME until 2019. Action for ME was the patient charity involved in the PACE trial. Rintatolimod Rintatolimod is a double-stranded RNA drug developed to modulate an antiviral immune reaction through activation of toll-like receptor 3. In several clinical trials of CFS, the treatment has shown a reduction in symptoms, but improvements were not sustained after discontinuation. Evidence supporting the use of rintatolimod is deemed low to moderate. The US FDA has denied commercial approval, called a new drug application, citing several deficiencies and gaps in safety data in the trials, and concluded that the available evidence is insufficient to demonstrate its safety or efficacy in CFS. Rintatolimod has been approved for marketing and treatment for persons with CFS in Argentina, and in 2019, FDA regulatory requirements were met for exportation of rintatolimod to the country. Prognosis Information on the prognosis of CFS is limited, and the course of the illness is variable. According to the NICE guideliene, CFS "varies in long-term outlook from person to person." Complete recovery, partial improvement, and worsening are all possible. Symptoms generally fluctuate over days, weeks, or longer periods, and some people may experience periods of remission. Overall, "many will need to adapt to living with ME/CFS." Some people who improve need to manage their activities in order to prevent relapse. Children and teenagers are more likely to recover or improve than adults. A 2005 systematic review found that for untreated CFS, "the median full recovery rate was 5% (range 0–31%) and the median proportion of patients who improved during follow-up was 39.5% (range 8–63%)," and that 8 to 30% of patients were able to return to work. Age at onset, a longer duration of follow-up, less fatigue severity at baseline, and