Novavax: >90% efficacy in UK but 60% in South Africa, hints of lower effect in HIV positive participants

Simon Collins, HIV i-Base

On 28 January 2021, Novavax released preliminary top-line results from two studies using it’s NVX-CoV2373 spike protein-based vaccine candidate. [1]

This was at the same time as concern about the B.1.351 variant first started to dominate news in the UK. [1]

The phase 3 study run in the UK enrolled more than 15,000 participants between 18-84 years of age, including 27% over the age of 65. It reported 89.3% efficacy (95% CI: 75.2 to 95.4), based on the first occurrence of PCR-confirmed symptomatic (mild, moderate or severe) COVID-19, at least 7 days after the second study vaccination.

This analysis was based on 62 cases, 56 vs 6 in the placebo vs active group, respectively. Of the 62 cases, 61 were mild or moderate, and 1 was severe (in placebo group). Approximately half the cases were the B.1.1.7 variant and a post hoc analysis calculated 95.6% efficacy against the original COVID-19 strain and 85.6% against B.1.1.7.

Results from a phase 2b study in 4,400 participants in South Africa reported 60% efficacy (95% CI: 19.9 to 80.1) in the 94% of participants who were HIV negative. This was based on 44 cases in 2,536 participants: 29 vs 15 in the placebo vs active groups, respectively. Data available for 27/44 showed 92% to be the B. variant.

However, when results from the 148 (6%) of HIV positive participants were added, overall efficacy dropped to 49.4% (95% CI: 6.1 to 72.8). This was due to worse outcomes in the vaccine group: 2.6% vs 5.5% had symptoms in the placebo vs active group. Although these figures are in the wrong direction, the wide confidence intervals means this might not be a real effect.

Importantly. roughly one-third of the 4,400 participants (not included in the analysis) were seropositive at baseline indicating previous COVID-19 infection. This was likely the pre-variant strain, but most infections during the study were with the B.1.351 variant. So although the vaccine provided sginificant although not complete protection against the B.1.351 variant.


Novavax press statement. Novavax COVID-19 vaccine demonstrates 89.3% efficacy in UK phase 3 trial. (28 January 2021).

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