A preliminary analysis suggests that AstraZeneca’s AZD1222 vaccine is effective against COVID-19 caused by the highly-transmissible UK variant, according to a statement Friday by its partners at the University of Oxford. The findings, which are not peer-reviewed and were released as a preprint by The Lancet, showed that AZD1222 was nearly as effective against symptomatic COVID-19 caused by the B.1.1.7 variant as it has been against older lineages.
Sarah Gilbert, chief investigator on the trial, suggested that while AZD1222 appears to be effective against B.1.1.7, it might need to be adapted for a future variant. “We are working with AstraZeneca to optimise the pipeline required for a strain change should one become necessary,” she said. AstraZeneca’s vaccine was authorised in the UK for emergency supply in late December, and more recently garnered conditional marketing authorization in the EU.
The latest analysis is based on phase 2/3 vaccine efficacy studies in the UK in which volunteers were randomized to receive AZD1222 or a MenACWY control vaccine. Participants provided weekly upper airway swab samples that were tested for SARS-CoV-2, with positive samples sent off for sequencing. The efficacy analysis included symptomatic COVID-19 in seronegative participants with a positive swab more than 14 days after a second dose of vaccine.
Vaccine also cuts duration of shedding, viral load
Researchers said that from the period between October 1 and January 14, there were 499 volunteers who developed COVID-19 infection. For primary symptomatic cases in which sequence data were available, 34 cases were due to the B.1.1.7 variant and 86 were non-B.1.1.7 infections. Vaccine efficacy was found to be similar in both these groups, at 74.6% and 84.1%, respectively, with overlapping confidence intervals. For cases of asymptomatic/unknown symptom infection obtained from weekly self-swabs, vaccine efficacy was higher for non-B.1.1.7 infections at 75.4% than for B.1.1.7 at 26.5%, although the authors noted that “fewer cases were available for analysis.” Specifically, for asymptomatic infections or those with unknown symptoms, there were 14 cases due to the B.1.1.7 variant and 30 due to non-B.1.1.7 lineages. Meanwhile, overall efficacy against the B.1.1.7 variant from all cases was 66.5%, compared with 80.7% against other variants.
Investigators also reported that viral load among volunteers with a positive swab who received the AZD1222 vaccine was significantly lower than among controls, and they were PCR-positive for a significantly shorter period of time as well. Results also showed that virus neutralisation activity by vaccine-induced antibodies was nine-fold lower against the B.1.1.7 variant than against other lineages, with the study authors suggesting that as overall protection was similar, other parts of the immune system are playing a key role. “Taken with our recent analysis, which showed a 67% reduction in any PCR-positive result after a single dose of [AZD1222], our findings suggest that even those vaccinees with a PCR-positive swab may be less likely to transmit the virus than an unvaccinated PCR-positive individual,” the authors stated, adding “these observations provide strong support for mass vaccination as a tool to control pandemic coronavirus.”
Meanwhile, the Oxford team said researchers in South Africa are still trying to determine how effective AZD1222 is against another strain first detected in that country. However, Mene Pangalos, executive vice president of biopharmaceuticals R&D at AstraZeneca, said it would not be surprising to see reduced efficacy against this B.1.351 variant, which studies suggest may be better at escaping the immune response. “I think it’s reasonable to say that what we know from other vaccines is, we’re not going to be surprised to see reduced efficacy,” he said, “because we’ve seen from the Johnson & Johnson vaccines and from the Novavax vaccines that these variants do impact – at least in mild and moderate disease or mild disease – efficacy.”
Pangalos noted that an ongoing phase 3 study in the US will also include data on virus variants, as well as showing more definitively how effective the vaccine is in people age 65 and over. Results from the trial are expected in the next four to six weeks.
In separate news, AstraZeneca said that based on early data from a trial, its AZD1222 vaccine appeared to offer only limited protection against mild disease caused by the B.1.351 variant. “In this small Phase I/II trial, early data has shown limited efficacy against mild disease,” and “we have not been able to properly ascertain its effect against severe disease and hospitalization given that subjects were predominantly young healthy adults,” a company spokesman said.