Stories of symptoms that subside after the shots are intriguing, experts told me. But no clinical trials have tested whether the vaccines can act as makeshift therapeutics for long COVID, either. It’s still unclear how common these ebbs in illness are, or how fleeting they might be. In patient-led surveys, at least as many long-haulers are reporting no postvaccination change in symptoms; a small percentage said that the shots have so far made their illness worse…

In long-COVID survivors whose immune systems have struggled to evict bits of the virus, Iwasaki told me, the vaccines might marshal a wave of antibodies and T cells—some of the body’s most essential fighters—that boots out these unwanted tenants and their scrappy remains. Alternatively, the vaccines could restore balance to an unhinged immune system, refocusing its resources on guarding against pathogens instead of attacking healthy tissues. There’s precedent for this, Iwasaki said: Some treatments for autoimmune conditions, such as multiple sclerosis, counterintuitively involve riling up other branches of the immune system. This last possibility is perhaps the most precarious, as it could be “a temporary suppression” of the long-haul condition, she told me. Lutchmansingh, at Yale, likened the idea to “a kick in the pants for the immune system.”

The emotional relief that many people feel after receiving their shots, and their confidence in the protection of vaccination, could also be helping long-haulers, Rutishauser, of UCSF, told me. The vaccine is “associated with a return to normalcy,” she said. The improvements documented so far shouldn’t be dismissed as a meaningless placebo effect, she added: Physical and psychological well-being can spur each other forward as some people’s sickness abates.