According to a Phase 1b-2 trial published in the New England Journal of Medicine, the two-dose COVID-19 vaccine developed by Oxford University / AstraZeneca Plc (NASDAQ: AZN) was ineffective against mild-to-moderate infections caused due to mutated virus strain in South Africa, dubbed as B.1.351 variant.
What Happened: The study was led by scientists at the South African Medical Research Council Vaccines and Infectious Diseases Analytics Research Unit.
The trial evaluated the safety and the efficacy of the AstraZeneca ChAdOx1 nCoV-19 vaccine in HIV-negative adults aged between 18 to 64 years of age. Median follow-up after the second dose was 121 days. Data showed that the vaccine was overall 10.4% effective against the variant.
Of the 750 participants vaccine recipients, 19 (2.5%) developed mild to moderate COVID-19 more than 14 days after the second dose, compared with 23 of 717 placebo recipients (3.2%).
The incidence of COVID-19 among the vaccine group was 731 per 1,000 person-years, compared with 93.6 per 1,000 person-years among the placebo group, for the efficacy of 21.9%.
Of the 42 total cases of COVID-19, 39 were caused by B1351, for vaccine effectiveness against this variant of 10.4%.
All 42 cases were mild to moderate, and no patients were hospitalized. The serious adverse event rates were similar between the vaccine and placebo groups.
Only one severe vaccine-related event occurred, a fever of 40°C (104°F) following the first dose; the fever cleared within 24 hours, and no adverse events were seen after the participant's second dose.
Why It Matters: The study concluded by saying that although the development of second-generation COVID-19 vaccines against strains such as B1351 and P1 has begun, the only vaccines likely to be available for the rest of 2021 are formulated against the original virus.
In early February, South African health officials stopped the AstraZeneca-Oxford vaccine's rollout to investigate reports that it offered little protection against mild-to-moderate disease.
Instead, the country switched to using the Johnson & Johnson (NYSE: JNJ) vaccine to immunize healthcare workers.
Price Action: AZN shares are down 0.14% at $49.98 in premarket trading on the last check Wednesday.