With the global devastation of Covid-19 continuing into 2021, the month of November marks a turning point in the pandemic timeline. A number of sponsors have released Phase III vaccine trial results in this month with all vaccines displaying good efficacy and generally well-tolerated safety profiles. mRNA vaccines BNT162b2 and mRNA-1273, developed by Pfizer/BioNTech and Moderna, respectively, both demonstrated a 95% level of efficacy. Prior to the pandemic no mRNA vaccines had been approved for human use, therefore the successful results obtained from BNT162b2 and mRNA-1273 Phase III clinical trials have allowed for optimism in this research space. Nonetheless, a significant issue concerning mRNA vaccines is the storage conditions, with Pfizer’s and Moderna’s vaccines requiring environments of -70 °C and -20°C, respectively—although Moderna’s candidate is able to be stored at fridge and room temperatures for short periods of time.
Vaccine storage is less of an issue for AstraZeneca’s vaccine candidate AZD1222, as it requires storage conditions between 2°C to 8°C, allowing for easier transportation and administration across a variety of settings. However, both mRNA vaccines have superior efficacies compared with AZD1222, which displays an efficacy of 70%. Numerous questions remain with regards to the results obtained in the AZD1222 Phase III study: the results were pooled from two cohorts, with one group receiving two identical doses one month apart and the other group accidentally receiving half a dose followed by a full dose the following month.
The smaller second cohort presented with a superior efficacy of 90% compared with the 62% observed in the first group. Many remain skeptical of this apparent serendipity, as the second group constitutes participants ages 55 and below, therefore individuals in this cohort may be less likely to become critically ill, which could allow for better efficacy results. It is likely that AstraZeneca will conduct a new trial to validate the increased efficacy observed in the cohort dosed incorrectly.
Sputnik V, an adenovirus-based vaccine produced by the Russian state-run Gamaleya research centre, has also shown in results from its Phase III trials whereby the vaccine was shown to display an efficacy of 95%, equal to that of the mRNA vaccines. Sputnik V requires storage conditions of -18°C or lower, similar to that of the Moderna vaccine, with further trials ongoing testing a freeze-dried version that could be stored between 2°C to 8 °C.
The Pfizer/BioNTech vaccine has recently been granted emergency use approval in the UK following a rolling review by the Medicines and Healthcare Products Regulatory Agency (MHRA). The UK has now become the first Western nation to grant approval for a Covid-19 vaccine. Shortly after the UK’s approval, Russian president Vladimir Putin announced his intent to initiate a national voluntary vaccination program next week with the Sputnik V vaccine, which was granted approval by the Russian regulatory authorities in August. Pressure is now on for other countries to issue approvals; the FDA has received Emergency Use Authorization applications within the last month from both Pfizer/BioNTech and Moderna, and has scheduled public hearings for them on 10 and 17 December respectively. Prior to the hearings, the FDA is scheduled to released summarised assessments of the applications, with the final authorisation taking place after the hearings.