US Market Breakdown: Moderna Soars as Yields Bite, Week of 17 August 2026

The story of the week on Wall Street was not really written in shares at all. It was written in the US government bond market, where the 30-year Treasury yield climbed to 5.34% on Tuesday, its highest level since 2007, and pulled equities down with it. By Friday's close the S&P 500 had lost 1.43% over the five sessions to finish at 7,674.37, the Nasdaq Composite had shed 2.05% to 26,180.45, and the Dow Jones Industrial Average had fallen 0.85% to 53,277.01. That was a second consecutive weekly decline for the Dow and the end of a three-week winning run for the S&P 500, which had set an all-time high the week before.

Two individual companies defined everything else. Moderna rose 177% in a single session on Wednesday on a Phase 3 cancer vaccine result — the biggest day in the company's history. Walmart fell 9% on Thursday, its worst day in more than four years, and was the single heaviest drag on a Dow that shed 703.84 points.

Monday's session, on 24 August, handed the market a fresh problem: a sell-off in semiconductors ahead of Nvidia's results.

Wall Street

The week began badly and got worse before it got better. On Monday 17 August the S&P 500 fell 0.52% to 7,745.06, the Nasdaq slipped 0.32% to 26,644.91 and the Dow lost 272.63 points, or 0.51%, to 53,459.78. The trigger was twofold: the expiry of the US–Iran ceasefire, which sent Brent crude to $90 a barrel, and a bond market in which the 30-year Treasury yield rose almost six basis points to 5.31%, a level last seen in 2007.

Tuesday was worse for technology. The 30-year yield pushed on to 5.34% and the 10-year reached 4.74%, close to the highest of President Trump's second term. The S&P 500 fell 0.69%, the Dow dipped 0.22%, and the Nasdaq — far more sensitive to the discount rate applied to future profits — dropped 1.33%.

Wednesday brought an intervention. The US Treasury announced it would at least double the size of its bond buyback operations, lifting the maximum per-operation amount for repurchases of 10-, 20- and 30-year debt to at least $4bn from $2bn. Yields fell sharply and all three indices rose 0.2%: the S&P 500 to 7,707.98, the Dow to 53,463.05 and the Nasdaq to 26,331.09. The Russell 2000 index of smaller US companies gained 0.5% to 3,032.94.

The relief lasted one day. On Thursday long-dated yields climbed back above where they had been before the announcement, and the market concluded that the Treasury's firepower was not equal to the forces pushing against it. The Dow fell 703.84 points, or 1.32%, to 52,759.21, the S&P 500 lost 0.87% to 7,641.16 and the Nasdaq gave up 1% to 26,067.17. Friday recovered a slice of that, with the Dow up 517.80 points, or 0.98%, the S&P 500 up 0.43% and the Nasdaq up 0.43%.

Monday 24 August, the most recent completed session, went the other way again. The Dow rose 140.15 points, or 0.26%, to 53,417.16, but the S&P 500 slipped 0.28% to 7,652.86 and the Nasdaq fell 0.76% to 25,980.19 as chip stocks sold off.

The week's biggest movers

Moderna was the standout, and not by a small margin. Shares closed Wednesday up 177% at $174.38 after the company and partner Merck announced that intismeran autogene — an individualised mRNA cancer therapy, previously known as mRNA-4157 — met its primary endpoint of recurrence-free survival in the Phase 3 INTerpath-001 melanoma trial when combined with Merck's Keytruda. It was Moderna's best day ever, and Bloomberg reported that short sellers took paper losses of roughly $5.5bn on it.

Merck itself rose 12% to $152.20 on the same news. The percentage gap between the two reactions is simply a matter of scale: Merck's market value sits near $333bn against Moderna's roughly $25bn, so the same trial result moves the smaller company far more violently. For Merck, the read-across matters because Keytruda faces loss of exclusivity later this decade.

Walmart was the week's biggest large-cap faller, dropping 9% on Thursday despite beating on both revenue and earnings. More on why in the earnings section below.

Estée Lauder jumped sharply on Wednesday — quoted between 16% and 18% higher across the session — after fourth-quarter sales and margins beat expectations and management guided to organic net sales growth of 3% to 5% for its 2027 financial year.

Tesla had its strongest week since May, rising roughly 5%, on two pieces of news: reports that the Cybercab — the company's first vehicle with no steering wheel or pedals — is close to launch, and confirmation of a 3 September event in Austin, Texas.

Coinbase, Robinhood and Strategy all rallied hard as bitcoin gained 22% on the week. Strategy rose around 29% and Coinbase around 25% across the five sessions, with Robinhood up almost 14% on Friday alone.

Micron was Monday's worst performer among the large chipmakers, falling 5.8%, with Advanced Micro Devices off more than 3% and Broadcom down more than 2%. The iShares Semiconductor ETF fell 2.7%.

Company news in focus

Meta Platforms went on trial in federal court in Oakland, California, with jury selection on Monday 17 August and opening statements the following day. A coalition of state attorneys general alleges the company designed Facebook and Instagram to be addictive to young users and misled the public about the risks. The trial is expected to run around seven weeks, and Mark Zuckerberg and Instagram head Adam Mosseri are both expected to testify. Meta shares fell 3.63% on the Monday the case opened.

On Thursday the Nevada Transportation Authority unanimously approved three commercial robotaxi permits covering Clark County, home to Las Vegas — a rare piece of regulatory news that helped three listed companies at once. Tesla was cleared for up to 5,000 vehicles, Alphabet's Waymo unit for up to 1,000, and Uber for a further 1,000 operated through partnerships. Together the permits allow up to 8,000 robotaxis over twelve months.

Crypto policy moved too. President Trump hosted exchange executives at the White House on Wednesday — including Coinbase chief executive Brian Armstrong and Robinhood's Vlad Tenev — and urged Congress to pass the Digital Asset Market Clarity Act, which would define which tokens count as securities and which as commodities. The Senate is expected to take the bill up when it returns from recess on 15 September.

Micron also faced renewed attention on its long-running patent dispute with Netlist, in which a jury awarded $445m in damages in 2024. Netlist's most recent quarterly filing shows the appeal is scheduled for oral argument at the Federal Circuit on 9 September. Separately, the Federal Trade Commission filed an amicus brief on Friday in an antitrust case alleging that Amgen improperly acquired exclusive rights to patent applications covering its Enbrel treatment.

Earnings in focus

It was the big week for American retail results, and the reactions were revealing. Walmart reported second-quarter revenue of $187.9bn — roughly £138bn at the $1.36 rate against sterling that prevailed on Friday — up 5.9% and ahead of consensus, with adjusted earnings per share of $0.81, up 19.1%. It also raised full-year guidance. The shares still fell 9%, because US comparable sales grew only 2.6% and because the raised full-year adjusted EPS range of $2.80 to $2.87 sat below the roughly $2.90 analysts had pencilled in. A useful reminder for UK readers that American retailers are judged on the trajectory of guidance, not the headline beat.

Target did the opposite, rising around 5%. Comparable sales grew 3.8% against expectations nearer 2.4%, traffic rose 3.6%, and the company lifted its full-year outlook to about 5% sales growth with EPS of $9.90 to $10.90. The caveat was prominent in the coverage: $752m of net earnings, or $1.65 per share of the $4.11 reported, came from tariff refunds. Stripping those out, earnings still grew 20%.

Home Depot reported quarterly sales of $47.9bn, up 5.7%, with comparable sales up 1.7% and adjusted diluted EPS of $4.92 against $4.68 a year earlier, and reaffirmed its full-year guidance. Management flagged pressure from fuel and energy input costs and continued weakness in larger discretionary projects, and the shares were little changed.

Lowe's beat on adjusted EPS at $4.40 but trimmed guidance, narrowing full-year sales to about $92bn from $92bn–$94bn and adjusted EPS to about $12.25 from a $12.25–$12.75 range, citing soft DIY demand. Comparable sales rose just 0.2%, with Pro and online strength offsetting DIY weakness. Estée Lauder was the week's cleanest beat, with quarterly revenue of $3.63bn against a $3.55bn forecast.

Sectors in focus

Information technology was comfortably the weakest S&P 500 sector over the week, shedding more than 3%. The indices tell the same story: the Nasdaq's 2.05% weekly fall was more than double the Dow's 0.85%, and on Tuesday the Nasdaq lost 1.33% on a day the Dow gave up only 0.22%.

This is the concentration problem in plain sight. When a handful of megacap technology companies make up an outsized share of the S&P 500's market value, a bond-driven repricing of long-duration growth assets can drag the headline index lower even on days when much of the rest of the market holds up. UK investors who own a US tracker hold a substantial position in that small group of companies.

Energy was the obvious beneficiary of the week's other big move. Oil rose for a second consecutive week on fading hopes of the Strait of Hormuz reopening, with WTI finishing around $87 a barrel, up more than 5%, and Brent trading near $94. That supported the large US-listed producers, Exxon Mobil and Chevron among them.

Health care was the standout on Friday, when gains in Merck and Johnson & Johnson helped drive the Dow's 517-point advance, while financials were lifted by the crypto-linked names as bitcoin surged.

Macro and the Fed

Minutes of the Federal Reserve's 28–29 July meeting were published on Wednesday and made uncomfortable reading for anyone expecting cuts. The Federal Open Market Committee held the federal funds target range at 3.50%–3.75%, but the decision drew three dissents, with regional presidents Logan, Hammack and Kashkari all voting for a 25 basis point increase. Officials indicated that further tightening would likely be necessary if inflation did not come down. The statement was little changed from June and offered no forward guidance, consistent with Chair Kevin Warsh's stated reluctance to signal the policy path in advance.

Bond yields were the week's dominant force. The 30-year Treasury yield reached 5.34%, its highest since 2007, and the 10-year touched 4.74%. The pressure reflects heavy government borrowing, a flood of long-dated supply, inflation that has been above the Fed's 2% target for five years, and — a newer factor — around $1.7tn of corporate bond issuance so far in 2026, up 27% on last year, a large slice of it funding AI infrastructure.

Treasury Secretary Scott Bessent's response, doubling bond buybacks, worked for a day. Gold gained nearly 5% on the week, with spot bullion around $4,588 an ounce on Friday, as a softer dollar and anxiety about US government debt drew buyers back. Bitcoin's 22% weekly gain was helped by a short squeeze that liquidated roughly $2.7bn of positions.

Still to come

Nvidia's numbers on Wednesday are the cleanest available read on whether the AI capital expenditure cycle is still intact, and they land in the same session as the Fed's preferred inflation measure. Warsh's Jackson Hole debut on Friday is the first extended statement of his framework from a podium long used to signal policy turns.

This article is for information and education only. It is not financial advice or a recommendation to buy, sell or hold any investment. Always do your own research.