The American biotechnology firm Novavax announced Thursday evening that its vaccine was 89.3% effective, according to the results of phase 3 trials. Good news offset by less effectiveness on the South African variant, considered to be more contagious, according to the first data.

Clinical trials of the two-dose Covid-19 vaccine of Novavax have shown an efficacy of 89.3%, the US biotech company said Thursday in a press release posting the results of the phase 3 trials. "NVX-CoV2373 has the potential to play an important role in addressing this global public health crisis, ”said company CEO Stanley Erck.

But the news was offset by the joint announcement that the vaccine is much less effective against the variant first identified in South Africa, which scientists consider to be more contagious.

The company will immediately embark on the development of a new vaccine targeting this variant, the statement said.

95.6% against the initial strain, and 85.6% against the English variant

British Prime Minister Boris Johnson welcomed the "good news" on Twitter, adding: "Our medical regulatory authorities will now assess the vaccine (...). If it is authorized, we have an order of 60 million doses ".

The vaccine was one of six candidates backed by the US government that had funded the project to the tune of $ 1.75 billion.

Clinical trials are also underway in the United States and Mexico, with 16,000 and 30,000 participants respectively.

The clinical trials, conducted in the UK, involved 15,000 people aged 18 to 84, 27% of whom were over 65.

The first interim analysis was based on 62 cases of Covid-19, of which 56 were observed in the placebo group, against six cases among those who received the NVX-CoV2373 vaccine.

The company's preliminary analysis indicates that the variant first identified in England, B.1.1.7, has been detected in more than 50% of confirmed cases.

The efficacy of the vaccine by strain of the coronavirus was estimated at 95.6% against the original strain, and at 85.6% against the variant that appeared in the United Kingdom.

Much lower efficiency on the South African variant

But the efficacy appears much lower in a smaller study conducted in South Africa.

The latter involved a little over 4,400 patients, from September to mid-January, a period during which the B.1.351 variant spread widely across South Africa.

According to the company, this variant was responsible for 90% of the cases that were the subject of sequencing.

The overall vaccine efficacy was 49.4% in these trials, but the number rose to 60% among the 94% HIV-negative participants.

Novavax said it began research on new vaccines against emerging variants in early January, and expects to screen optimal vaccine candidates in the coming days, before starting clinical trials in the second quarter.