On Thursday, April 16, Cochrane published a systematic review of seventeen clinical trials involving 20,342 participants and concluded that anti-amyloid drugs for Alzheimer's disease produce "no clinically meaningful" effect on cognitive decline or dementia severity, while increasing the risk of brain bleeding and swelling. [1] The review singled out lecanemab (Leqembi, Biogen/Eisai) and donanemab (Kisunla, Eli Lilly) as the two disease-modifying drugs currently approved in the United States and elsewhere. Its lead author, Francesco Nonino of Bologna's IRCCS Institute of Neurological Sciences, said the evidence had converged on a conclusion that early statistically-significant trial results did not translate to clinically meaningful benefit. [2]

Today is Day Seven. The silence from the four institutions the Cochrane finding most directly challenges — the Food and Drug Administration, the Centers for Medicare and Medicaid Services, Biogen, and Eli Lilly — now clears two full trading weeks. The paper's position, carried through Sunday's Day Five and Monday's Day Six, is that the silence past the duration of any recent peer-review-without-regulator-response is structural. It is not waiting for an internal committee to convene. It is not preparing a rebuttal. Medicare is still paying for the infusions. That is the position. The paper's position has hardened each day. Today it clears the threshold at which the pattern becomes the response.

Consider the arithmetic. Leqembi entered broader Medicare coverage in July 2023 after the FDA converted the drug's accelerated approval to traditional approval. [3] CMS's statement at the time tied coverage to participation in a CMS-facilitated registry. Cost per patient runs to approximately $26,500 annually for the drug itself, not including infusion services, MRI monitoring for amyloid-related imaging abnormalities (ARIA), or neurology follow-up. Kisunla followed in July 2024, priced in the same range. Medicare covers both. The Cochrane review found the absolute effect of these drugs on cognitive decline to be "well below" the minimum clinically important difference threshold. [1] No one at CMS has commented on whether the new evidence triggers any coverage review. No one at the FDA has commented on whether the new evidence triggers any safety re-labeling. Biogen has not posted a response to its investor-relations page. Lilly has not. The Alzheimer's Society in the UK acknowledged the review on April 15 and continued to endorse the drugs. [4] The UK's National Institute for Health and Care Excellence has rejected both for cost-effectiveness reasons. The transatlantic divide — FDA-approved, NICE-rejected — is the clinical finding's most visible policy artifact, and it predates this review.

What is different now is the evidence. A Cochrane systematic review is, by design, the slowest-produced and most-contested form of medical-evidence aggregation. It does not generate news cycles; it closes them. The drugs Cochrane looked at — lecanemab, donanemab, solanezumab, gantenerumab, bapineuzumab, and two others — had generated seventeen trials and 20,342 patient-years of data. The meta-analysis resolved that data into a single finding: the drugs remove amyloid from the brain, and the removal does not produce clinical benefit. Brain swelling and bleeding ("ARIA-E" and "ARIA-H" in the literature) are confirmed side effects of drugs that do not help. This is the type of finding that, in a different regulatory-reimbursement architecture, would trigger a review cycle with a defined end date.

No such cycle has been triggered. On Friday, two days after Cochrane, CMS's Alzheimer coverage page still described Leqembi as an FDA-approved treatment with broader traditional-approval coverage available. [3] Today, a week later, it still does. The pipeline — diagnosis, MRI screening, amyloid PET, infusion, ARIA monitoring, continued infusion — runs. Any individual neurologist's decision to adjust prescribing is a clinical matter. The structural fact, captured by CMS's continued payment, is that the reimbursement pipeline does not respond to evidence-based findings about efficacy at the pace of the evidence.

This is what the paper means by silence-as-policy. The FDA does not need to speak to maintain an approval; the absence of an action is the action. CMS does not need to update a National Coverage Determination to continue paying; the pipeline continues until explicitly interrupted. Biogen and Lilly do not need to respond to a Cochrane review to continue sales; their shareholders have already priced in the Cochrane risk (Biogen's share price is down on the month, though not catastrophically — the market reads the silence the same way the paper does). The institutional arrangement is that, once a drug clears the approval-and-coverage gateway, the evidence bar for removing it is structurally higher than the evidence bar for adding it.

The paper notes this as a finding, not a scandal. The drugs might still help some patients; the population-level Cochrane finding does not foreclose that possibility. Individual neurologists will continue to make individual judgments. But the policy layer — the layer at which taxpayer money flows into the infusion chair — is, on the evidence of seven days, structurally unresponsive to the most-weighted evidence review available to it. Day Seven is the moment that stops being "we are waiting for a statement" and starts being "no statement was ever coming."

The silence from Day Seven will now be read, for the paper's purposes, as the institutional answer. The next Cochrane-adjacent event — a CMS letter, an FDA label change, an investor-call disclosure, a coverage review — will be covered. Until then, the silence is the policy; the pipeline is the decision.

-- NORA WHITFIELD, Chicago