Question 1

How many shares of BIIB does PRIMECAP MANAGEMENT CO/CA/ own?

Accepted Answer

As of 2026-Q1, PRIMECAP MANAGEMENT CO/CA/ holds 14.8M shares of BIIB (BIOGEN INC).

Question 2

What is PRIMECAP MANAGEMENT CO/CA/'s BIIB position worth?

Accepted Answer

As of 2026-Q1, PRIMECAP MANAGEMENT CO/CA/'s BIIB position is worth $2.7B.

Question 3

Is PRIMECAP MANAGEMENT CO/CA/ buying or selling BIIB?

Accepted Answer

In 2026-Q1, PRIMECAP MANAGEMENT CO/CA/ decreased their BIIB position (0.0% change in shares).

Question 4

When did PRIMECAP MANAGEMENT CO/CA/ first buy BIIB?

Accepted Answer

Based on available 13F filings, PRIMECAP MANAGEMENT CO/CA/ first reported a position in BIIB in 2026-Q1. They have held the position across 30 quarters.