Novavax’s Covid-19 vaccine offers some protection against the rapidly spreading coronavirus variants detected in the UK and SA, researchers announced on Thursday night.
But, worryingly, they also reported that previous infection with older lineages is unlikely to provide protection against the highly contagious 501Y.V2 variant that has driven SA’s second coronavirus wave.
Wits University led an SA phase 2b trial of the vaccine, which demonstrated 60% efficacy against mild and severe Covid-19 among the 94% of trial participants who were HIV negative, and 49% efficacy overall.
Approximately 90% of the infections that occurred among trial participants were caused by the new variant, according to preliminary analysis.
The variant, which was first detected in Nelson Mandela Bay last October and has rapidly become the dominant lineage throughout SA, has prompted several countries to impose travel bans on SA visitors.
While the results are not as good as those from a larger phase 3 trial conducted in the UK, where a different variant dominates, they are nevertheless encouraging because they show 501Y.V2 has some sensitivity to the Novavax vaccine, said the researchers.
The Novavax vaccine, NVX-CoV2373, is a protein-based vaccine engineered from the genetic sequence of SARS-CoV-2, the virus that causes Covid-19. A phase 3 trial conducted in the UK, where the B.1.1.7 variant is dominant, showed 89% efficacy.
Less sensitive
Slightly more than half (55%) of the UK cases were attributed to the B.1.1.7 variant, according to preliminary analysis.
"The higher efficacy of the vaccine in the UK than in SA is because the variants circulating in SA are less sensitive to vaccine-induced immune responses. Nevertheless, the 60% reduced risk against Covid-19 illness in vaccinated individuals in SA underscores the value of this vaccine to prevent illness from the highly worrisome variant currently circulating in SA, and which is spreading globally.
"This is the only Covid-19 vaccine for which we now have objective evidence that it protects against the variant dominating in SA," said Shabir Madhi, executive director of the Vaccines and Infectious Diseases Analytics Research Unit at Wits and principal investigator in the Novavax Covid-19 vaccine trial in SA.
"The public health value of vaccines extends beyond a simple point estimate. The ability of Covid-19 vaccines to impact the pandemic will depend on the product, its efficacy, and how quickly we can scale up coverage of the vaccine eventually," he said in a statement.
The SA phase 2b study enrolled over 4,400 participants from August 2020, with Covid-19 cases counted from September to mid-January. During this time, the 501Y.V2 variant was widely circulating in SA.
Preliminary genetic sequencing data from the Covid-19 cases in the SA trial show that 92.4%, or 25 out of 27 infections, were due to 501Y.V2.
Local data
Worryingly, one third of the volunteers who participated in the trial were "sero-positive", indicating they had previously been infected with Covid-19. Based on the dates of the trial, these pretrial infections were probably caused by the prototype, or non-variant, virus.
"These SA data emphasise the importance of conducting vaccine trials in SA, so that we can evaluate the efficacy of vaccines in the local context.
"These data have significant public health implications, because they are the first to report the efficacy of a Covid-19 vaccine against the N501Y.V2 variant and demonstrate the real risk of reinfection," says Madhi.
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