Regeneron Pharmaceuticals, Inc.
MX ˙ BMV ˙ US75886F1075
SecurityMX:REGN / Regeneron Pharmaceuticals, Inc.
InstitutionFlagship Harbor Advisors, Llc
Latest Disclosed Ownership744 shares
Latest Disclosed Value $ 574,861
Flagship Harbor Advisors, Llc ownership in REGN / Regeneron Pharmaceuticals, Inc.

On April 28, 2026 - Flagship Harbor Advisors, Llc filed a 13F-HR form disclosing ownership of 744 shares of Regeneron Pharmaceuticals, Inc. (MX:REGN) valued at $574,861 USD as of March 31, 2026. The entity filed a previous 13F-HR on January 21, 2026 disclosing 870 shares of Regeneron Pharmaceuticals, Inc.. This represents a change in shares of -14.48% during the quarter.

Flagship Harbor Advisors, Llc has a history of taking positions in derivatives of the underlying security (REGN) in the form of stock options. The firm currently holds call options representing 0 of underlying shares valued at $0 USD .

Note: prior versions of this page mistakenly stated that the share values represented the number of options, not the number of underlying shares. For more information on the data backing these reports, please see the SEC document Frequently Asked Questions About Form 13F.

Institutional Ownership: 13F and NPORT Filings

The Security and Class in the table below are shown exactly as filed by the investor. We do our best to track continuity of investments through acquisitions, and this will be reflected in the table as changes in names. In addition to descriptive data, performance of the investment is shown over time. To calculate quarterly performance, we first calculate cost basis of the shares purchased during the quarter, then use that to calculate gross profit. Quarterly return is Gross Profit / Starting Portfolio value.

Note that cost basis is calculated and stored in thousands, so small quarterly changes in shares frequently result in a cost basis of zero.

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Institutional Put/Call Ratios
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In addition to reporting standard equity and debt issues, institutions with more than 100MM assets under management must also disclose their put and call option holdings. Since put options generally indicate negative sentiment, and call options indicate positive sentiment, we can get a sense of the overall institutional sentiment by plotting the ratio of puts to calls. The chart to the right plots the historical put/call ratio for this instrument.

Using Put/Call Ratio as an indicator of investor sentiment overcomes one of the key deficiencies of using total institutional ownership, which is that a significant amount of assets under management are invested passively to track indices. Passively-managed funds do not typically buy options, so the put/call ratio indicator more closely tracks the sentiment of actively-managed funds.

MX:REGN / Regeneron Pharmaceuticals, Inc. Historical Put/Call Ratio
Disclosed Equity Positions (from 13F/NPORT Filings)
File
Date
Effective
Date
Form Security Class ID Avg Price
Paid (Est)
Reported
Shares
ΔShares ΔShares
(%)
Reported
Value
(x1000)
ΔValue
(%)
Alloc
(%)
ΔAlloc ΔAlloc (%) Cost Basis
(x1000)
Unrealized
Gain/Loss
(x1000)
2026-04-28 2026-03-31 13F REGENERON PHARMACEUTICALS COM 75886F107 744 -126 -14.48 575 -14.46 0.0253
2026-01-21 2025-12-31 13F REGENERON PHARMACEUTICAL Common Stock 75886F107 870 -25 -2.79 672 33.40 0.0317
2025-11-05 2025-09-30 13F REGENERON PHARMACEUTICALS COM 75886F107 895 5 0.56 503 7.71 0.0219
2025-08-04 2025-06-30 13F REGENERON PHARMACEUTICALS COM 75886F107 890 890 467 0.0221
2025-01-21 2024-12-31 13F REGENERON PHARMACEUTICALS COM 75886F107 0 -244 -100.00 0 -100.00
2024-10-21 2024-09-30 13F REGENERON PHARMACEUTICALS COM 75886F107 244 -8 -3.17 257 -3.03 0.0141
2025-12-02 2024-06-30 13F REGENERON PHARMACEUTICALS COM 75886F107 252 -7 -2.70 265 6.02 0.0159
2024-04-16 2024-03-31 13F REGENERON PHARMACEUTICALS COM 75886F107 259 19 7.92 249 18.57 0.0160
2024-01-10 2023-12-31 13F REGENERON PHARMACEUTICALS COM 75886F107 240 240 211 0.0153
2023-07-11 2023-06-30 13F REGENERON PHARMACEUTICALS COM 75886F107 0 -957 -100.00 0 -100.00
2023-04-12 2023-03-31 13F REGENERON PHARMACEUTICALS COM 75886F107 957 189 24.61 786 41.88 0.0741
2023-01-13 2022-12-31 13F REGENERON PHARMACEUTICALS COM 75886F107 768 442 135.58 554 146.22 0.0568
2022-10-13 2022-09-30 13F REGENERON PHARMACEUTICALS COM 75886F107 326 326 225 0.0261
2021-02-08 2020-12-31 13F REGENERON PHARMACEUTICAL Common Stock 75886F107 0 -222 -100.00 0 -100.00
2020-10-13 2020-09-30 13F REGENERON PHARMACEUTICAL Common Stock 75886F107 222 -57 -20.43 124 -28.32 0.0167
2020-07-31 2020-06-30 13F REGENERON PHARMACEUTICAL Common Stock 75886F107 279 110 65.09 173 108.43 0.0254
2020-05-12 2020-03-31 13F REGENERON PHARMACEUTICAL Common Stock 75886F107 169 -156 -48.00 83 -31.97 0.0166
2020-02-14 2019-12-31 13F REGENERON PHARMACEUTICAL Common Stock 75886F107 325 0 0.00 122 35.56 0.0214
2019-10-22 2019-09-30 13F REGENERON PHARMACEUTICAL Common Stock 75886F107 325 -47 -12.63 90 -22.41 0.0176
2019-07-22 2019-06-30 13F REGENERON PHARMACEUTICAL Common Stock 75886F107 372 9 2.48 116 -22.15 0.0241
2019-04-15 2019-03-31 13F REGENERON PHARMACEUTICAL Common Stock 75886F107 363 -29 -7.40 149 2.05 0.0306
2019-01-26 2018-12-31 13F REGENERON PHARMACEUTICAL COM 75886F107 392 -36 -8.41 146 -13.61 0.0355
2018-11-05 2018-09-30 13F REGENERON PHARMACEUTICAL Common Stock 75886F107 428 -34 -7.36 169 6.29 0.0313
2018-08-14 2018-06-30 13F REGENERON PHARMACEUTICAL Common Stock 75886F107 462 462 159 0.0318
Disclosed Call Options
File
Date
Effective
Date
Form Security Class ID Opt Avg Share
Price
Shares ΔShares
(%)
Value
(x1000)
ΔValue
(%)
Prior Allocation
(%)
Allocation
(%)
ΔAllocation
(%)
Cost Basis
(x1000)
Profit
(x1000)
Return
(%)
2020-05-12 2020-03-31 13F REGENERON PHARM Listed Options Call 0 -100.00 0 -100.00 n/a n/a n/a
2020-02-14 2019-12-31 13F REGENERON PHARM Listed Options Call 4 0.00 37 362.50 n/a n/a n/a
2019-10-22 2019-09-30 13F REGENERON PHARM Listed Options Call 4 8 n/a n/a n/a
Legend
Shares
The total number of shares held by the institution at the end of the reporting period (the effective date). This is provided in the filing.
Value
The total value of the shares as of the effective date. This is provided in the filing.
Avg. Share Price
The weighted average share price of the shares held by the institution. We use FIFO accounting to determine this price
Class
This is the security class as indicated by the filer. There are a variety of values for this field. Common values include "EC" = equity common, "EP" - equity preferred
Allocation (%)
The percent of the institution's portfolio that this position represents. This is provided in NPORT filings. For 13F filings, we calculate it.
Change in Allocation
The change in allocation from the prior reporting period. This is calculated as current allocation - prior allocation.
Change in Allocation (%)
The percent change in allocation from the prior reporting period. This is calculated as (current allocation - prior allocation) / prior allocation.
Cost Basis
The total cost of the shares held. This is calculated as reported shares * avg. share price
Unrealized Gain/Loss
This is the market value of the position as of the effective date minus the cost basis.