Moderna was the most-bought stock for retail traders in the week leading up to its 16% single-day plunge

• Moderna was retail investors' most-bought stock in the five days to Tuesday - before the company plunged 16% on Wednesday.
• Retail investors also snapped up vaccine-maker Pfizer, according to data company VandaTrack.
• But Wall Street is conflicted on the sector after its stellar rally, with BofA calling Moderna's price "ridiculous."

Moderna was the most-bought stock among retail investors in the five days to Tuesday - before plunging 16% on Wednesday as Wall Street balked at the vaccine company's sky-high share price.

Vaccine-makers were a favorite pick for retail investors in the five trading days from August 4 to August 10, figures from data company VandaTrack on Wednesday showed.

Moderna, an mRNA developer that produced a 95% pandemic-ending vaccine in under one year, was top of the bunch with $159 million of net purchases. Investors were likely drawn in by the stock's 17% jump to a record high on Monday, boosted by the potential for third booster shots and other news that day suggesting strong demand for Moderna's COVID-19 vaccine.

Pfizer was fifth on VandaTrack's list, with $107 million of net purchases.

But, as also seen in Chinese stocks, institutional investors appear to have become more wary about the vaccine space than retail traders. Bank of America published a note on Tuesday slamming Moderna's stock price, saying it had gone from "unreasonable to ridiculous." It has climbed more than 460% over the past year.

The bearish note and potential regulatory issues helped send Moderna and German vaccine-maker BioNTech tumbling on Wednesday, with the latter dropping 14%. Pfizer fell 4%.

Moderna was down 6.3% for the week at Wednesday's close, while BioNTech was down 12%.

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BofA's Geoff Meacham said investors were being wildly optimistic about Moderna's future performance. The bank thinks the stock is worth $115, 70% below Wednesday's closing price of $385.33.

VandaTrack's analysts said outsized retail flows were likely largely responsible for the rally in vaccine makers over the last few weeks.

But institutional investors appear more conflicted after the companies' astounding gains. Wall Street analysts' average 12-month price target for Moderna is $277.07, 28% below the stock's closing price on Wednesday, and it has more "hold" than "buy" ratings.

At the same time, analysts' average target for BioNTech is $267.10, undershooting Wednesday's closing price of $359.19 by 25%, according to Bloomberg data.

Despite Moderna and BioNTech's plunge, VandaTrack said many retail traders are still on course to make gains through their purchases of call options - contracts that let investors buy a stock at a certain price on or before a set date.

Moderna rose 2.6% in early trading Thursday, while BioNTech climbed 4.6%.