Mar 31, 2026 filings. Quarterly 13F reports arrive up to 45 days after quarter end; this register is filed through May 29, 2026.
971 institutional managers reported holding BIIB for the quarter ended Mar 31, 2026. Together they hold about 89% of shares outstanding; the top 10 hold 55%. 124 opened new positions; 131 closed out. Complete ranked register from SEC 13F filings.
| manager | shares | % out | value (Mar 31, 2026 close) | change | held since |
|---|---|---|---|---|---|
| Vanguard Group | 17.60M | 11.86% | $3.23B | added +0.6% | ≤2013 |
| BlackRock | 15.97M | 10.77% | $2.93B | added +7.9% | ≤2013 |
| PRIMECAP Management | 14.76M | 9.94% | $2.71B | unchanged | ≤2013 |
| FMR (Fidelity) | 12.81M | 8.63% | $2.35B | added +35.9% | ≤2013 |
| State Street | 7.17M | 4.83% | $1.31B | unchanged | ≤2013 |
| Geode Capital | 4.34M | 2.93% | $796.3M | added +3.4% | ≤2013 |
| Wellington Management | 2.96M | 2.00% | $543.1M | trimmed -16.6% | ≤2013 |
| Morgan Stanley | 2.17M | 1.46% | $398.1M | trimmed -6.6% | ≤2013 |
| AQR Capital | 1.92M | 1.30% | $352.7M | added +25.8% | ≤2013 |
| UBS | 1.90M | 1.28% | $348.6M | trimmed -6.5% | ≤2013 |
| Invesco | 1.75M | 1.18% | $320.0M | added +5.4% | ≤2013 |
| Boston Partners | 1.70M | 1.15% | $311.7M | trimmed -1.2% | 2025 Q4 |
| Northern Trust | 1.45M | 0.97% | $265.3M | unchanged | ≤2013 |
| Legal & General Group PLC | 1.35M | 0.91% | $247.5M | trimmed -7.5% | ≤2013 |
| T. Rowe Price Investment Management, INC. | 1.16M | 0.78% | $212.9M | added +49.1% | 2023 Q2 |
| Bank OF America CORP /DE/ | 1.16M | 0.78% | $212.0M | added +2.4% | ≤2013 |
| Charles Schwab Investment Management | 1.15M | 0.78% | $210.8M | unchanged | ≤2013 |
| VAN ECK Associates CORP | 1.08M | 0.73% | $198.0M | added +1.3% | ≤2013 |
| Dimensional Fund Advisors | 1.08M | 0.73% | $197.9M | added +12.3% | ≤2013 |
| Deutsche Bank AG\ | 1.06M | 0.72% | $195.1M | added +11.5% | 2013 Q3 |
| Goldman Sachs | 1.05M | 0.71% | $192.7M | trimmed -4.4% | ≤2013 |
| Pictet Asset Management Holding SA | 913.3k | 0.61% | $167.5M | trimmed -3.6% | ≤2013 |
| Point72 | 809.6k | 0.55% | $148.5M | trimmed -71.2% | 2024 Q4 |
| Alyeska Investment Group | 805.0k | 0.54% | $147.6M | trimmed -21.4% | 2025 Q2 |
| Amundi | 790.8k | 0.53% | $145.0M | added +38.2% | 2016 Q1 |
| BNY Mellon | 788.5k | 0.53% | $144.6M | trimmed -2.8% | ≤2013 |
| Robeco Institutional Asset Management B.v. | 763.2k | 0.51% | $139.9M | added +24.9% | ≤2013 |
| Fred Alger Management, LLC | 733.2k | 0.49% | $134.4M | trimmed -8.2% | 2025 Q1 |
| MFS Investment Management | 720.6k | 0.49% | $132.1M | added +1.1% | ≤2013 |
| Employees Provident Fund Board | 704.2k | 0.47% | $129.1M | unchanged | 2019 Q4 |
| BNP Paribas Financial Markets | 687.2k | 0.46% | $126.0M | trimmed -8.9% | ≤2013 |
| First Trust Advisors LP | 674.0k | 0.45% | $123.6M | added +19.1% | ≤2013 |
| T. Rowe Price | 672.4k | 0.45% | $123.3M | trimmed -15.1% | ≤2013 |
| Balyasny Asset Management | 650.0k | 0.44% | $119.2M | added +6.9% | 2020 Q3 |
| AustralianSuper Pty LTD | 616.2k | 0.41% | $113.0M | added +29.2% | 2025 Q1 |
| Artemis Investment Management LLP | 571.6k | 0.39% | $104.8M | added +152% | 2025 Q4 |
| Barclays PLC | 551.5k | 0.37% | $101.1M | trimmed -57.7% | ≤2013 |
| Royal Bank OF Canada | 531.4k | 0.36% | $97.4M | trimmed -1.9% | ≤2013 |
| Zurcher Kantonalbank (Zurich Cantonalbank) | 522.2k | 0.35% | $95.7M | added +15.4% | ≤2013 |
| Caisse de depot et placement du Quebec | 518.7k | 0.35% | $95.1M | trimmed -11.9% | 2025 Q1 |
| Citigroup INC | 500.5k | 0.34% | $91.8M | trimmed -12.8% | ≤2013 |
| Hsbc Holdings PLC | 463.7k | 0.31% | $85.0M | trimmed -8% | ≤2013 |
| Swiss National Bank | 430.6k | 0.29% | $79.0M | added +7.2% | ≤2013 |
| National Pension Service | 401.7k | 0.27% | $73.7M | added +39.8% | 2014 Q3 |
| Mitsubishi UFJ Asset Management CO., LTD. | 399.5k | 0.27% | $73.3M | added +3.7% | ≤2013 |
| Candriam S.c.a. | 381.8k | 0.26% | $70.0M | added +15.5% | 2014 Q4 |
| Patient Capital Management, LLC (focused) | 379.7k | 0.26% | $69.6M | trimmed -34.1% | 2024 Q1 |
| Nuveen | 358.8k | 0.24% | $65.8M | trimmed -4.5% | ≤2013 |
| Sumitomo Mitsui Trust Group, INC. | 356.3k | 0.24% | $65.3M | trimmed -3.9% | ≤2013 |
| CalPERS | 340.9k | 0.23% | $62.5M | added +3.1% | ≤2013 |
Largest 50 of 971 shown; the full ranked, searchable register is at boothcheck.com/holders/BIIB. Related filers are grouped using the filings' own included-manager declarations. Historically, several managers opening new positions in the same quarter said almost nothing about the quarter that followed (59,118 cases since 2013). A filed record, not a forecast. Nothing here is investment advice.