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Prothena Corp Public Ltd Co

PRTA
Exchange
Nasdaq
Industry
Pharmaceutical Preparations
SEC CIK
0001559053

In the last 90 days, Prothena Corp Public Ltd Co insiders filed 10 open-market purchases and 0 sales; 189 institutions reported holding it in 13F filings for Q2 2026, worth $462.7M in total; no superinvestor holds it.

Four kinds of short-selling data, each measuring something different:

  • Short interest: shares sold short and not yet bought back, as of a settlement date. FINRA publishes it twice a month, about eight business days after the settlement date.
  • Daily short volume: shares sold short each day in off-exchange trades reported to FINRA. It counts trades, not open positions, and is published the next day.
  • Fails-to-deliver: shares not delivered by the settlement date. The SEC publishes them twice a month, about two weeks late.
  • ATS (dark pool) volume: weekly volume on alternative trading systems and other off-exchange venues. FINRA publishes it two to four weeks after the week.

More in the glossary.

Short interest

Shares sold short and not yet bought back, from FINRA, on every settlement date in the last two years.

Short interest
7.91M
Shares, settlement Oct 30, 2026
Change
−28.5K
−0.4% vs. Oct 15, 2026
Days to cover
15.69
Short interest ÷ average daily volume
Average daily volume
504.2K
Shares, as reported by FINRA
Short interest by settlement date
Oct 31, 2024: 7,531,620 sharesNov 15, 2024: 7,877,213 sharesNov 29, 2024: 8,057,302 sharesDec 13, 2024: 8,797,843 sharesDec 31, 2024: 8,770,252 sharesJan 15, 2025: 9,349,701 sharesJan 31, 2025: 8,900,074 sharesFeb 14, 2025: 9,034,843 sharesFeb 28, 2025: 9,129,265 sharesMar 14, 2025: 8,779,086 sharesMar 31, 2025: 8,384,570 sharesApr 15, 2025: 7,922,712 sharesApr 30, 2025: 7,453,961 sharesMay 15, 2025: 8,952,748 sharesMay 30, 2025: 4,414,727 sharesJun 13, 2025: 4,655,763 sharesJun 30, 2025: 4,330,532 sharesJul 15, 2025: 4,757,454 sharesJul 31, 2025: 4,374,625 sharesAug 15, 2025: 4,184,841 sharesAug 29, 2025: 4,055,435 sharesSep 15, 2025: 3,763,878 sharesSep 30, 2025: 3,845,694 sharesOct 15, 2025: 3,857,015 sharesOct 31, 2025: 4,144,115 sharesNov 14, 2025: 4,657,490 sharesNov 28, 2025: 4,639,338 sharesDec 15, 2025: 4,699,126 sharesDec 31, 2025: 6,584,532 sharesJan 15, 2026: 7,069,471 sharesJan 30, 2026: 7,063,694 sharesFeb 13, 2026: 7,083,043 sharesFeb 27, 2026: 6,854,767 sharesMar 13, 2026: 7,044,790 sharesMar 31, 2026: 7,016,080 sharesApr 15, 2026: 7,076,832 sharesApr 30, 2026: 6,871,465 sharesMay 15, 2026: 7,097,854 sharesMay 29, 2026: 7,737,902 sharesJun 15, 2026: 7,866,857 sharesJun 30, 2026: 8,369,568 sharesJul 15, 2026: 8,196,964 sharesJul 31, 2026: 8,172,438 sharesAug 14, 2026: 8,545,127 sharesAug 31, 2026: 8,495,796 sharesSep 15, 2026: 8,544,664 sharesSep 30, 2026: 8,010,864 sharesOct 15, 2026: 7,939,666 sharesOct 30, 2026: 7,911,160 shares
Short interest in PRTA by settlement date
Settlement dateShort interestChangeChange %Avg. daily volumeDays to cover
Oct 30, 20267.91M−28.5K−0.4%504.2K15.69
Oct 15, 20267.94M−71.2K−0.9%597.8K13.28
Sep 30, 20268.01M−533.8K−6.3%580.9K13.79
Sep 15, 20268.54M+48.9K+0.6%322.0K26.53
Aug 31, 20268.50M−49.3K−0.6%341.9K24.85
Aug 14, 20268.55M+372.7K+4.6%436.9K19.56
Jul 31, 20268.17M−24.5K−0.3%585.3K13.96
Jul 15, 20268.20M−172.6K−2.1%499.7K16.40
Jun 30, 20268.37M+502.7K+6.4%759.4K11.02
Jun 15, 20267.87M+129.0K+1.7%492.3K15.98
May 29, 20267.74M+640.0K+9.0%558.7K13.85
May 15, 20267.10M+226.4K+3.3%547.7K12.96
Apr 30, 20266.87M−205.4K−2.9%374.8K18.33
Apr 15, 20267.08M+60.8K+0.9%461.5K15.33
Mar 31, 20267.02M−28.7K−0.4%569.6K12.32
Mar 13, 20267.04M+190.0K+2.8%628.9K11.20
Feb 27, 20266.85M−228.3K−3.2%398.1K17.22
Feb 13, 20267.08M+19.3K+0.3%390.8K18.12
Jan 30, 20267.06M−5.78K−0.1%508.2K13.90
Jan 15, 20267.07M+484.9K+7.4%490.2K14.42
Dec 31, 20256.58M+1.89M+40.1%827.4K7.96
Dec 15, 20254.70M+59.8K+1.3%692.8K6.78
Nov 28, 20254.64M−18.2K−0.4%514.5K9.02
Nov 14, 20254.66M+513.4K+12.4%631.1K7.38
Oct 31, 20254.14M+287.1K+7.4%513.9K8.06
Oct 15, 20253.86M+11.3K+0.3%718.7K5.37
Sep 30, 20253.85M+81.8K+2.2%764.7K5.03
Sep 15, 20253.76M−291.6K−7.2%830.2K4.53
Aug 29, 20254.06M−129.4K−3.1%1.04M3.89
Aug 15, 20254.18M−189.8K−4.3%1.25M3.34
Jul 31, 20254.37M−382.8K−8.1%806.4K5.42
Jul 15, 20254.76M+426.9K+9.9%868.6K5.48
Jun 30, 20254.33M−325.2K−7.0%2.50M1.73
Jun 13, 20254.66M+241.0K+5.5%1.21M3.84
May 30, 20254.41M−4.54M−50.7%3.01M1.47
May 15, 20258.95M+1.50M+20.1%2.40M3.72
Apr 30, 20257.45M−468.8K−5.9%624.3K11.94
Apr 15, 20257.92M−461.9K−5.5%663.7K11.94
Mar 31, 20258.38M−394.5K−4.5%456.5K18.37
Mar 14, 20258.78M−350.2K−3.8%446.6K19.66
Feb 28, 20259.13M+94.4K+1.1%428.7K21.30
Feb 14, 20259.03M+134.8K+1.5%291.6K30.98
Jan 31, 20258.90M−449.6K−4.8%336.5K26.45
Jan 15, 2025Revised9.35M+579.7K+6.6%462.8K20.20
Dec 31, 20248.77M−27.6K−0.3%968.0K9.06
Dec 13, 20248.80M+740.5K+9.2%485.0K18.14
Nov 29, 20248.06M+180.1K+2.3%452.0K17.82
Nov 15, 20247.88M+345.6K+4.6%440.9K17.87
Oct 31, 20247.53M+746.4K+11.0%472.3K15.95

Fails-to-deliver

Shares that weren't delivered by the settlement date, from the SEC, for the last 30 dates with fails. The price is the previous day's closing price published by the SEC.

Fails-to-deliver in PRTA by settlement date
Settlement dateSharesPriceValue
Sep 29, 2026318$8.72$2.77K
Sep 24, 20263,531$8.68$30.6K
Sep 21, 20265,860$8.58$50.3K
Sep 11, 2026535$9.02$4.83K
Sep 9, 2026349$9.54$3.33K
Sep 2, 202623$9.61$221.03
Aug 31, 20266,503$9.33$60.7K
Aug 26, 202620$9.42$188.4
Aug 25, 202621$9.39$197.19
Aug 18, 2026183$8.88$1.63K
Aug 17, 202663$8.86$558.18
Aug 6, 2026368$8.49$3.12K
Aug 3, 20268,398$8.12$68.2K
Jul 30, 20261$8.56$8.56
Jul 23, 20268,290$8.44$70.0K
Jul 13, 2026397$9.24$3.67K
Jul 8, 2026200$9.68$1.94K
Jul 7, 2026200$9.50$1.90K
Jul 6, 2026200$9.69$1.94K
Jul 2, 2026200$9.58$1.92K
Jul 1, 2026200$9.79$1.96K
Jun 18, 2026241$8.49$2.05K
Jun 15, 2026365$8.25$3.01K
Jun 11, 2026339$7.91$2.68K
Jun 9, 2026288$8.56$2.47K
Jun 2, 2026225$9.59$2.16K
May 26, 2026480$9.83$4.72K
May 21, 2026327$9.35$3.06K
May 20, 20261,627$9.07$14.8K
May 19, 20263,392$9.59$32.5K

Daily short volume

Off-exchange short-sale volume, not short interest: shares sold short each day in trades reported to FINRA, for the last 30 trading days.

The short volume ratio isn't a sentiment gauge: market makers sell short to fill buy orders and to hedge, so short sales are usually about half of off-exchange volume.

Off-exchange short volume in PRTA by trade date
Trade dateShort volumeShort exemptOff-exchange volumeShort volume ratio
Nov 12, 202652,11212184,29961.8%
Nov 11, 202676,3980150,44150.8%
Nov 10, 202666,620623128,07352.0%
Nov 9, 2026252,1170304,46182.8%
Nov 6, 2026100,5590152,74765.8%
Nov 5, 202692,0710146,87862.7%
Nov 4, 202660,54920093,42664.8%
Nov 3, 202650,703086,17058.8%
Nov 2, 2026108,2890155,69669.6%
Oct 30, 202687,0960116,23674.9%
Oct 29, 202654,466082,85265.7%
Oct 28, 2026124,4260261,91147.5%
Oct 27, 202690,4090176,59951.2%
Oct 26, 2026207,7240296,06870.2%
Oct 23, 2026119,4518170,87669.9%
Oct 22, 2026145,4361,700182,05879.9%
Oct 21, 2026116,5040171,26568.0%
Oct 20, 202697,5290158,95161.4%
Oct 19, 202671,5760118,51160.4%
Oct 16, 202672,5350165,30543.9%
Oct 15, 202650,172087,66957.2%
Oct 14, 2026110,6420195,20956.7%
Oct 13, 2026203,6040273,16174.5%
Oct 12, 202685,5900175,74348.7%
Oct 9, 2026160,2490360,58344.4%
Oct 8, 2026201,7870278,93972.3%
Oct 7, 2026227,8251,019286,64679.5%
Oct 6, 2026111,8110164,35768.0%
Oct 5, 2026157,6141,900238,45966.1%
Oct 2, 2026185,9950261,45071.1%

ATS (dark pool) volume

Weekly volume on alternative trading systems (ATS) and other off-exchange (OTC) venues, from FINRA, for the last 12 weeks. ATS share is ATS volume ÷ (ATS + OTC volume), not a share of all trading.

Weekly ATS and OTC volume in PRTA
Week ofTierATS sharesATS tradesOther OTC sharesOther OTC tradesATS share
Oct 5, 2026T2783,74414,785599,7124,09856.7%
Sep 28, 2026T2525,39314,638705,7003,50842.7%
Sep 21, 2026T2418,64715,442413,4354,37350.3%
Sep 14, 2026T2373,74314,873431,8865,07346.4%
Sep 7, 2026T2215,20410,216191,7723,03252.9%
Aug 31, 2026T2261,76310,420240,4033,48252.1%
Aug 24, 2026T2364,55110,466222,6812,93562.1%
Aug 17, 2026T2275,98412,318308,7913,23847.2%
Aug 10, 2026T2411,22612,833335,3562,72755.1%
Aug 3, 2026T2462,07314,119272,9694,58862.9%
Jul 27, 2026T2684,47518,319304,8843,00269.2%
Jul 20, 2026T2548,02717,951393,4794,12658.2%