S&P 500 ends week 1.43% lower as capital rotates out of AI hardware into biotech, gold and crypto
S&P 500 week close: 7,674.37 (-1.43%) Nasdaq Friday close: 26,180.46 (+0.43%) Sentiment: mixed
The S&P 500 closed the week at 7,674.37, down 1.43%, as a 3.53% drawdown in information technology overwhelmed a 4.33% gain in health care. MRNA.US rose 129.20% on the week after Moderna and Merck reported on 19 August that their personalized mRNA cancer vaccine met its primary endpoint in a Phase 3 melanoma trial. The 30-year Treasury ended at 5.276% and the 10-year at 4.738%, yields that weigh hardest on the longest-duration AI names.
The week on Wall Street
The S&P 500 fell 111.39 points to 7,674.37 in the week to 21 August 2026, a 1.43% decline. The Nasdaq Composite lost 2.05% to 26,180.46 and the Dow gave up 0.85% to 53,277.01, a spread that follows each index's weight in AI hardware. The Russell 2000 fell 1.65% to 3,017.87 and the VIX closed at 15.13, up 6.18% for the week after a Thursday peak close of 16.01.
Moderna and Merck released Phase 3 results for intismeran autogene on Wednesday 19 August, the first successful late-stage trial of a custom mRNA cancer therapy, and MRNA.US more than doubled in a single session, the first time an S&P 500 member has done that since 2008. MRK.US gained 12.30% across the week and the S&P health care sector printed an all-time closing high. The same session brought FOMC minutes showing many officials open to further rate hikes, and Treasury Secretary Scott Bessent's surprise decision to at least double long-end bond buybacks.
Thursday 20 August produced the week's largest single-session decline, with the Dow off 703.84 points to 52,759.21 and the Russell 2000 down 1.34%. The Dow added 517.80 points back on Friday and every major index finished higher, though all three benchmarks still closed the week down.
Sector scorecard (5-day)
Health care led all eleven S&P 500 sectors in the week to 21 August 2026, gaining 4.33% on the sector SPDR proxies, while information technology fell 3.53%.
- Best: health care +4.33%, led by MRNA.US +129.20% and MRK.US +12.30%
- Energy +2.79% as Brent crude rose 6.63% to US$94.39 a barrel
- Materials +1.90% with gold up 6.85% to US$4,680.60 an ounce
- Worst: information technology -3.53%, utilities -3.48%, industrials -3.36%
- Dispersion (best minus worst): 7.86 points
Semiconductors and AI infrastructure led the tech decline. AVGO.US fell 6.24%, AMD.US 8.00%, NVDA.US 4.64% and optical component maker COHR.US 11.14%.
Top movers, week ending 21 August 2026
| Ticker | Week | Reason |
|---|---|---|
| MRNA.US | +129.20% | Phase 3 melanoma vaccine hit with Merck; 13.7% short interest squeezed |
| AMLX.US | +78.73% | Avexitide Phase 3 success, then a US$350m equity raise on 18 August |
| PURR.US | +58.38% | Largest listed HYPE treasury vehicle; bitcoin rose 22.68% on the week |
| MRVI.US | +51.58% | CleanCap mRNA reagent supplier re-rated on the Moderna readout |
| TEM.US | +39.52% | Personalis sequencing, bought for US$1.5b in July, underpins the vaccine |
| KLAR.US | -31.07% | Q2 beat, then full-year revenue guidance cut to US$4.08b to US$4.16b |
| AAP.US | -24.70% | Q2 revenue US$2b missed US$2.04b; DIY comparable sales down double digits |
| AEHR.US | -24.12% | Fell 10% on 19 August as chip test names sold, with Teradyne off 5% and FormFactor 6% |
| FN.US | -23.42% | Record Q4 revenue up 45%, stock still fell 20% on an AI optical valuation reset |
| SHAZ.US | -22.75% | AI neocloud sold with other AI infrastructure names; no company news since a US$373m contract on 4 August |
Friday US session
- S&P 500: 7,674.37 (+0.43%)
- Nasdaq: 26,180.46 (+0.43%)
- Dow: 53,277.01 (+0.98%)
- Russell 2000: 3,017.87 (+0.85%)
- VIX: 15.13 (-5.50%)
The S&P 500 opened Friday at 7,668.04, reached 7,695.65 and closed at 7,674.37, giving back roughly half its intraday advance into the bell. The Dow's 0.98% gain more than doubled the S&P 500 and Nasdaq moves, which both added 0.43%.
Bitcoin closed above US$77,000 for its best week since 2024, up 22.68% to US$77,258, and listed crypto names followed: COIN.US gained 25.61% and MSTR.US 28.17% across the week. Brent crude rose 0.65% on Friday to US$94.39, a sixth consecutive session of gains, after the 60-day Iran ceasefire lapsed.
Macro themes that played out
Minutes from the 28 to 29 July FOMC meeting, released at 2:00pm ET on 19 August, showed a growing number of officials concerned that inflation is not coming down fast enough, with many seeing a need for further rate hikes if it persists. The July decision itself was a 9 to 3 hold at a 3.50% to 3.75% target range, with three members dissenting in favor of an increase.
Bessent announced the same day that buybacks in the 10 to 30 year sector would at least double to a minimum of US$4 billion per operation, running from 9 September to 4 November. The 30-year yield fell as much as 9 basis points on the announcement before ending the week at 5.276%, still close to its highest level since 2007. The 10-year finished at 4.738%, up 4 basis points on the week, and the dollar index fell 0.83% to 98.84.
As of 18 August, Kalshi and Polymarket both put a September hold near 70.5 cents and a quarter-point hike near 28.5 cents, while fed funds futures priced the hike between roughly 31% and 35%. A cut sat at about 1%.
Week ahead, Mon to Fri (ET)
- Mon 24 Aug: Treasury Secretary Bessent holds a press conference on new Iran sanctions; Chicago Fed National Activity Index (July); PDD.US and XPeng report
- Tue 25 Aug: Consumer Confidence (August) and New Home Sales (July) at 10:00am; FHFA House Price Index (June) at 9:00am; Intuit reports
- Wed 26 Aug: Core PCE deflator (July) at 8:30am, consensus 3.2% annual against 3.3% in June; Q2 GDP second estimate and July durable goods orders at 8:30am; NVDA.US reports after the close alongside CRM.US and CRWD.US
- Thu 27 Aug: Jackson Hole symposium opens, running 27 to 29 August; weekly jobless claims at 8:30am; MRVL.US reports
- Fri 28 Aug: Fed Chair Kevin Warsh delivers his first Jackson Hole keynote, 19 days before the 16 September FOMC decision; Chicago PMI (August); final University of Michigan sentiment (August); preliminary annual payrolls revision
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