AstraZeneca has become the latest pharmaceutical company to reveal promising results in clinical trials, for its viral vector vaccine developed with the University of Oxford.

In a group given two full doses of the vaccine at least one month apart, the vaccine demonstrated 62% efficacy at preventing COVID. Interestingly, in another group initially given a half dose of vaccine, followed by a full dose, the efficacy was 90%.

This news follows similarly promising results for both Pfizer/BioNTech and Moderna’s mRNA vaccines. Press announcements indicated both had efficacy above 90% in preventing symptomatic COVID-19.

It’s important to remember none of these results have yet been published in a peer-reviewed journal. It’s also important to consider that while these figures are encouraging, they don’t necessarily tell us everything we need to know about how well the vaccines will work in the real world.

What’s next? From efficacy to effectiveness

At this stage, Australia has signed up for the Pfizer and AstraZeneca vaccines should they meet the relevant safety and efficacy standards and gain regulatory approval.

Pfizer has applied to the US Food and Drug Administration (FDA) for an emergency use authorisation, while AstraZeneca has said it will “immediately” prepare to submit its data to regulatory authorities around the world.

The FDA and any other regulators that receive applications — likely including the Therapeutic Goods Administration in Australia — will assess the vaccines on a case-by-case basis. They will consider the target population to receive the vaccine (for example, older people or health-care workers), the characteristics of the vaccine, and all relevant evidence on the vaccine’s safety and efficacy we have so far from preclinical and human trials.

The regulators will also need to decide whether to authorise the vaccine for groups who were excluded from the trial, such as pregnant women. In any event, this emergency use authorisation is an early, or conditional approval, as the phase 3 trials are still ongoing.

Over time, we’ll accumulate more data on the safety and efficacy on these three vaccine candidates, as participants complete the phase 3 trials, and possibly from further clinical trials including different groups who were initially excluded. For example, further studies might evaluate the vaccine’s safety and efficacy in immunosuppressed people or pregnant women.

The early efficacy results from the Pfizer, Moderna and AstraZeneca trials are very encouraging. They may lead to an emergency use authorisation in selected populations, with vaccines potentially rolling out in the coming months.

However, we’re only at the beginning of the story. As we transition from these trials to the real world, we must continue to monitor whether any approved vaccine is safe and effective — not just efficacious — across the spectrum of the population.