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June 17, 2021

Why did CureVac's Covid-19 vaccine disappoint? Here's what experts say.

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    CureVac on Wednesday released the results of its combined Phase 2/3 trial for its Covid-19 vaccine, which found the vaccine was just 47% effective at preventing Covid-19, a significantly lower level of protection than provided by other Covid-19 vaccine candidates so far.

    Your top resources on the Covid-19 vaccines

    Details on the trial

    The results are from a 40,000-person trial in 10 countries that began in December 2020, conducted in partnership with Bayer AG. CureVac's Covid-19 vaccine—like those developed by Pfizer-BioNTech and Moderna— uses mRNA technology, but it doesn't use a chemically modified version of mRNA as Pfizer and Moderna do, according to the Washington Post.

    CureVac has released few details on the trial so far, as it plans to release a fuller analysis during a company call Thursday. But the initially reported efficacy rate of 47% falls below the 50% threshold that FDA and the World Health Organization have stated would be required to provide emergency authorization for use of a new vaccine.

    CureVac's early data suggests that one reason for the low efficacy may be that many study participants were infected with new coronavirus variants, against which existing vaccines are less effective. Specifically, among the 135 people in the trial who developed Covid-19, only one was infected by the original coronavirus. A total of 13 coronavirus variants were detected in the trial, and 57% of Covid-19 cases in the trial were infected by variants deemed "variants of concern" by public health authorities.

    "While we were hoping for a stronger interim outcome, we recognize that demonstrating high efficacy in this unprecedented broad diversity of variants is challenging," Franz-Werner Haas, CureVac's CEO, said in a statement.

    "They're testing their vaccine much later than all the other vaccines we have were tested, and there are a lot more variants out there that could confound the ability of a vaccine to protect," Deborah Fuller, a vaccine scientist at the University of Washington, said.

    However, while all authorized vaccines have shown lower efficacy against new variants, other vaccines still appear to outperform CureVac's vaccine. For instance, the New York Times notes that in a study in Qatar, the Pfizer vaccine—which was about 95% effective against the original coronavirus strain—reduced infections with the alpha variant by about 87% to 89.5% and reduced infections with the beta variant by 72.1% to 75%.

    Next steps

    CureVac is currently working alongside GlaxoSmithKline to develop a second-generation vaccine in the hopes of developing a Covid-19 vaccine that can protect against multiple coronavirus variants by next year.

    As for its first Covid-19 vaccine, Haas said the company intends to move forward. "We're going to full speed for the final readout," he said. "We are still planning for filing for approval."

    Natalie Dean, a biostatistician at the University of Florida, said the vaccine's efficacy might slightly improve by the end of the trial, but "it's not going to change dramatically."

    "It's up in the air," Fuller said. "I would not at this point say this is a failed vaccine, but people are going to make those comparisons."

    Because CureVac's vaccine can be stored at ordinary refrigerator temperatures, it was expected to play a significant role in vaccinating individuals in low- and middle-income countries. But based on the latest data, Jacob Kirkegaard, a vaccine supply expert at the Peterson Institute for International Economics, said he thinks it will be challenging for CureVac to compete with Novavax's Covid-19 vaccine.

    "I suspect it will be difficult for them to really get a significant developing-country market," he said (Johnson, Washington Post, 6/16; Zimmer, New York Times, 6/16; Loftus, Wall Street Journal, 6/17).

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