Researchers have identified viruses such as Epstein-Barr virus (EBV) that can reactivate after infection with COVID-19 and contribute to long-term COVID symptoms such as fatigue and brain fog.[2][1] EBV, which approximately 95% of adults carry in a latent form, is reawakened when the immune system is compromised by COVID.[2][4] In one study, 28.6% (40 of 140) of patients with persistent fatigue after COVID-19 had EBV reactivation, compared to 11.3% (9 of 80) in the control group.[1] Another study found that two-thirds of patients with long-term COVID showed signs of recent EBV activity, and those with more symptoms had higher antibody levels.[2][4] Latent tuberculosis (TB), which is carried by a quarter of the world's population, can also flare up as COVID reduces TB-suppressing immune cells.[2] These co-infections acquired before or during COVID may drive long-lasting symptoms, according to a review of 17 experts, although a causal relationship has not been confirmed.[2] Existing antibiotics and antiviral drugs could be repurposed to treat these infections.[2]