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A vial of the Phase 3 Novavax coronavirus vaccine is seen ready for use in the trial at St. George's Hospital in London, England. (AP/Yonhap News)

US pharmaceutical firm Novavax announced that its COVID-19 vaccine was 90.4% effective at preventing infection in late-stage trials in the US and Mexico. That was a little lower than the 96% efficacy in an earlier trial in the UK.

Novavax has contracted to supply 40 million doses to South Korea — enough to vaccinate 20 million people fully. Under the contract, it's supposed to deliver as many as 20 million doses in the third quarter of 2021. The company plans to apply for regulatory approval in the US and Europe in the third quarter.

Reuters and other news sources reported Monday that Novavax's vaccine had been 90.4% effective in a clinical trial on 29,960 volunteers aged 18 and above in the US and Mexico.

Two-thirds of the volunteers in the phase 3 trial received two doses of the actual vaccine three weeks apart, while the other third were given a placebo.

Among the 77 trial participants who had contracted COVID-19 by the end of April, 63 had received the placebo. All 14 of the vaccinated people who still contracted COVID-19 only had mild symptoms, Novavax said, which means the vaccine is 100% effective at preventing severe symptoms.

The Novavax vaccine is also highly effective (93.2%) at preventing the eight viral variants, including Alpha, which originated in the UK, and Beta, which originated in South Africa.

Novavax announced Friday that an analysis of the blood serum of 30 trial participants who'd received two doses of the vaccine found that the vaccine produced a strong neutralizing reaction against the Alpha and Beta variants of the coronavirus.

But that finding hasn't been printed in a leading medical journal and will still likely need to be reviewed.

The Novavax vaccine is a recombinant vaccine, made of protein subunits, in contrast with the mRNA method used by the Pfizer and Moderna vaccines and the viral vector method used by AstraZeneca. Other recombinant vaccines include the hepatitis B vaccine and the HPV vaccine.

That makes it probable that the Novavax vaccine will be safe and its effects long-lasting. Another advantage is that it can be distributed and stored in ordinary refrigerators.

Previously, Novavax announced that its vaccine had a 96% efficacy rate in a phase 3 trial carried out in the UK in March. There were no fatalities or severe symptoms among the 15,000 or so people who participated in that trial.

Novavax is expected to apply for authorization for emergency use in the US and the EU in the third quarter. It was originally thought that the firm would be able to apply as early as last month, but a delay in the phase 3 trial in the US pushed back the entire schedule.

Novavax CEO Stanley Erck said the company plans to apply for emergency use authorization in the third quarter, as soon as it meets the requirements of the Federal Drug Administration and regulatory agencies in other countries. Erck said that a large amount of the vaccine produced in the early stages will go to low- and middle-income countries.

The New York Times said that since more than 65% of Americans aged 18 and above have received at least one dose of a COVID-19 virus, other countries will probably need the Novavax vaccine more than the US.

The South Korean government had earlier announced that shipments of the Novavax vaccine would begin to arrive this month, but that schedule has been delayed until the third quarter. Novavax has concluded a supply contract with SK Bioscience that includes technology transfers.

By Choi Hyun-june, staff reporter

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