COVID-19 vaccine maker Moderna, Inc. (NASDAQ:MRNA) fell over 21% on Thursday after the company reduced its revenue guidance for the year, citing a highly competitive respiratory vaccine market in the U.S. and weak COVID-19 vaccine sales in Europe.

What Happened: Moderna stock plunged 21.01% to $94.17 on Thursday and fell an incremental 1.73% to $92.54 in premarket trading on Friday, according to Benzinga Pro data.

Cathie Wood's Ark Invest capitalized on the weakness and piled into the stock. On Thursday two of Ark's actively managed exchange-traded funds – the Ark Innovation ETF (NYSE:ARKK) and the ARK Genomic Revolution ETF (CBOE: ARKG), bought 202,991 shares of Moderna, valued at $19.12 million.

The buying is in line with Ark's strategy of using any potential weakness as a buying opportunity in its core portfolio holdings.

Moderna is ARKK's 24th biggest holding in value terms, with the flagship fund holding 736,884 shares valued at $69.39 million. ARKG holds 399,287 Modena shares valued at $37.60 million.

Why It's Important: Moderna, which is one of the pioneers of the mRNA new-vaccine technology, was among the frontrunners that launched vaccines for the virus causing the COVID-19 pandemic. The early-mover advantage has helped the company to make outsized profits from selling the vaccine.

As the pandemic abated, the company has done well to diversify its revenue stream. In late May, it received FDA approval for its respiratory syncytial vaccine. The company is also developing a slew of personalized cancer vaccines in collaboration with Merck & Co. (NYSE:MRK).

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