News of the positive trial data from Pfizer’s vaccine development added to the euphoria post the US elections bringing cheer to people and markets across the world. Whilst there is no taking away the promising nature of the data, here’s a practical guide to what to expect from here on, according to Anne Moore, a Senior Lecturer in Biochemistry and Cell Biology at the University College Cork.
“Preliminary data from the Pfizer/BioNTech COVID-19 vaccine trial suggests it provides 90% efficacy at preventing the disease. At the very least, this news will result in a large sigh of relief across the vaccine community. It signifies a breakthrough – it’s the first announcement that a vaccine can protect against SARS-CoV-2 infection in humans.
This shows it can be done. But how well it can be done is still a big question that no one has the answer to. These results are promising, but there’s a lot more we now need to confirm.”
These are just preliminary trials, long way to go:
“The 90% efficacy is a strong result, but we should remember that this is an interim analysis, based on 94 cases of disease that have occurred across those receiving either the vaccine or a placebo. Pfizer has noted in its trial protocol that it needs at least 164 cases of disease to occur across the study to reliably assess the vaccine’s efficacy.
If subsequent cases occur more frequently among those who have had the vaccine rather than the placebo, then this efficacy figure will fall. So we don’t yet know if this number is truly reflective of the vaccine’s protective ability – meaning crucially, we need to get to the end of the trial.”
How long will the vaccine’s effect last:
“….One key thing these interim results don’t tell us is how long protection lasts. Participants in this phase 3 trial received two doses of the vaccine, and measurement of its efficacy was taken seven days after the second dose was given. This is likely around the height of the initial immune response. It will be really important to understand how durable this initial protection is after this point.
A pessimist would hope for retaining efficacy for at least three months. An optimist would hope for retaining high levels of protection for a number of years. However, being realistic, this mRNA-based vaccine platform is new, and so we’ll need time to understand if and when the initial response starts to wane. We also need to understand if this vaccine and others in development can induce good memory responses from the immune system that will provide protection for years to come.”
Months to go before the final approval:
“…the US FDA has said it will consider authorising the vaccine for emergency use – ahead of full approval – once the trial has collected two months’ worth of safety data on half of the participants. Pfizer expects to have this available by the third week of November.
The trial will also continue for many months to come – in order to reach that reliability threshold of 164 cases of disease – and there will be further follow-ups looking at the vaccine’s safety and the immune responses and protection it elicits in different groups of participants.”
How many doses will be available and how soon?
“…even if approved, big challenges remain. Pfizer expects to have 50 million doses ready this year, enough to immunise 25 million people, and 1.3 billion by the end of 2021. Given the size of the world’s population – and the fact the vaccine requires two doses – universal coverage is a long way away.
The other vaccines in development therefore remain just as important. We will need more than one vaccine for global coverage, and to ensure we have the right one for each age and health cohort.
Overall, these results should be celebrated, but with the realisation that this is only one step in the journey. We still have a long way to go in getting the world back to normal – but the compass is pointing in the right direction.”

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