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A Covid-19 vaccine from Novavax proved nearly 90% effective in preliminary results from a key clinical trial in the United Kingdom, the company said, but in a separate trial appeared far less effective against a new variant of the coronavirus that was first identified in South Africa.

In its 15,000-volunteer U.K. trial, Novavax said, the vaccine prevented nine in 10 cases, including against a new strain of the virus that is circulating there. But in a 4,400-volunteer study in South Africa, the vaccine proved only 49% effective. In the 94% of the study population that did not have HIV, the efficacy was 60%. 

In the U.K. trial, Novavax observed 62 cases of symptomatic Covid-19, with 56 in the placebo group and six among volunteers who got the vaccine. One patient on placebo developed severe Covid-19, compared with zero in the vaccine group. The company provided few details on the vaccine’s safety, saying only that the serious side effects were rare and balanced between the studies’ vaccine and placebo groups.

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In the South African study, 29 cases of symptomatic Covid-19 were observed in the placebo group, and 15 in the vaccine group.

It’s unclear whether these data will be enough for U.S. approval, or if the U.S. will wait for further data, as it appears to be doing with vaccines developed by AstraZeneca and Oxford University. Novavax said it expects to file for an emergency authorization in the U.K. in the coming months, once it has final data from its clinical trial there. The company said it has been in contact with the Food and Drug Administration but didn’t provide details on its plans.

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Operation Warp Speed, the U.S. government’s vaccine incubator, is running its own large U.S. trial of the Novavax vaccine in the United States and Mexico. Researchers expect to complete enrollment in the first half of February.

Carlos del Rio, a professor of infectious diseases at the Emory University School of Medicine, said the overall efficacy numbers were impressive, and that the vaccine showed at least some efficacy against the variant first identified in South Africa.

By the same token, the lower efficacy against that variant could be a vulnerability in the United States, where it was first reported in South Carolina on Thursday, and elsewhere.

Nahid Bhadelia, medical director of the special pathogens unit at Boston Medical Center, emphasized that although the drop in efficacy against the South African variant is bad news, the results aren’t “a complete wash.” The vaccine, she said, “can still make a huge difference.” But the results also emphasize the important work of figuring out how to develop booster shots against new variants, especially given the news that the South Africa strain, B1351, was found in South Carolina.

Novavax said it is already at work on a new version of the vaccine designed to combat more infectious strains of SARS-CoV-2, which could work as a booster shot for people already inoculated. But clinical testing isn’t expected until the second quarter of this year.

Some experts cautioned against over-interpreting the efficacy results in the South Africa trial, noting that they amounted to a relatively small number of cases in a preliminary analysis.

“I am not sure that it is disappointing. The U.K. data look very good. The South Africa data may be more nuanced,” said Anna Durbin, a professor at the Johns Hopkins Bloomberg School of Public Health, noting that each trial defined symptomatic disease slightly differently. She said she would be interested in seeing more data on the severity of disease in the cases reported.

Scott Gottlieb, the former FDA commissioner and Pfizer board member, said he didn’t think it was a surprise that the vaccine was less effective against the new strain.

“We have already seen experimentally that there is a falloff in neutralization against that variant with the other vaccines, and we should expect that this may be common to all the vaccines that use the original spike protein as the epitope, regardless of how that protein is being delivered,” he said.

More data will be available with results from Johnson & Johnson, expected soon, because that trial will include patients from both Brazil and South Africa.

“I think this raises the stakes on putting boosters into development that are based on these new variants, and building a regulatory process that allows this sort of incremental, follow-on innovation to reach the market based on something short of brand new, full-blown outcomes studies,” Gottlieb said.

Novavax’s data arrive as countries around the world scramble to secure enough vaccine doses to protect their populations. In the U.S., the federal government has struggled to meet demand for doses of the only two authorized vaccines, from Moderna and partners Pfizer and BioNTech.

Novavax has said it expects to produce about 2 billion doses of its vaccine in 2021. The U.S. has signed a contract to buy 100 million of them and has the option to acquire more.

Like all the Covid-19 vaccines that are being used or are in final test, Novavax’s two-dose shot works by mimicking a protein called spike, which is found on the surface of SARS-CoV-2. When the immune system catches sight of that protein, it produces antibodies against it, thereby protecting the body from a case of Covid-19.

But Novavax is using the most tried-and-true technology among the frontrunners in the race to develop Covid-19. The first two vaccines authorized in the U.S. use a technology called mRNA, which slips genetic material into cells to create a protein that stimulates the immune system. Others still in development, such as one from Johnson & Johnson and another from AstraZeneca, use genetically altered viruses to do something similar.

Like some approved vaccines, Novavax’s vaccine manufactures fragments of the spike protein in insect cells and then adds another chemical, called an adjuvant, to stimulate the immune system to respond. This approach is used in an approved flu vaccine sold by Sanofi, and was the approach that Sanofi and GlaxoSmithKline planned to use in their own Covid-19 vaccine.

The similarities are not entirely coincidental. Gale Smith, the former chief scientific officer of the company that developed that vaccine, is now a scientist at Novavax.  But while the drug giants stumbled, Novavax, a small company that has not previously brought a product to market, has mostly hit its marks.

The company presented promising early data in August that showed neutralizing antibody levels that were roughly quadruple those seen in patients who had recovered from Covid-19, among the best for any vaccine in early testing. Those same results were published in the New England Journal of Medicine in September.

In July, Novavax received $1.6 billion in funding from Operation Warp Speed to scale up its manufacturing processes, with the agreement that the 100 million doses of vaccine that would result would be owned by the U.S. government.

The good news, said Natalie Dean, a biostatistician at the University of Florida, is that, from the start, several different vaccine technologies have been developed against Covid-19. That makes the world more ready for what comes next.

“This is why it’s important to have an open pipeline,” Dean said.  “At every stage we want to not put all our eggs in one basket. And this is the same situation. We still don’t know about durability, we don’t know how the vaccines work against different variants. At all stages we want a diversity of approaches.”

  • The AZ “trial” sounds flaky. They gave the wrong dose to half the patients and eligibility was for some reason restricted to only enter young patients. Doesn’t sound very professional.

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