The British laboratory AstraZeneca has just announced in a press release that the effectiveness of its vaccine against Covid-19 is 70%. What do we know exactly about these first intermediate results?
The American biotechnology company Moderna announced on November 16 that its vaccine candidate against the SARS-CoV-2 coronavirus was 94.5% effective . The announcement then came a week after that of the Pfizer and BioNTech laboratories, and their vaccine "effective at 95% to prevent Covid-19 infections. Also remember the 92% effectiveness of the vaccine from the Russian Gamaleya Institute.
The British laboratory AstraZeneca has just announced that the effectiveness of its vaccine was 70%. "Only? “, one would be tempted to say. "In absolute terms, though, 70% isn't bad. The flu vaccine, for example, never does better “, nuance in Le Monde the infectiologist Odile Launay who coordinates the clinical investigation center of Cochin-Pasteur.
As part of this "vaccine race" triggered by the pandemic, AstraZeneca has partnered with researchers at the University of Oxford to develop a vaccine with viral proteins called AZD1222.
In concrete terms, this is how it works:the surface of the new coronavirus is lined with small spikes allowing it to come into contact with the cells to be infected. These spikes are small viral proteins which can now be made in the laboratory and injected into the body by a relatively benign virus in order to make the antibodies react to these foreign molecules. Once trained to recognize these proteins, the immune system will then be able to defend itself if it comes into contact with them again.
In this case, "benign virus" is a weakened type of adenovirus, a pathogen that can cause colds and other mild infections in humans and some animals . The adenovirus used is the one that mainly infects chimpanzees.
The reported results of this vaccine are from a Phase III clinical trial conducted in the UK and Brazil, involving over 23,000 participants . The interim analysis was triggered when 131 cases occurred in subjects who received either two doses of AZD1222 or a comparator vaccine, MenACWY meningococcal vaccine. The efficacy rate was calculated based on the distribution of these 131 cases in the MenACWY group compared to the AZD1222 group.
Note that participants who received the AZD1222 vaccine were also divided into two groups. In the first, 2,741 subjects received a half dose of vaccine followed by a booster shot with a full dose. In this section, the approach was found to be approximately 90% effective to prevent Covid-19.
In the second group, 8895 participants receiving AZD1222 received two full doses of the vaccine. In this section, the approach was found to be about 62% effective to prevent disease. The pooled efficacy data therefore give an average efficacy of approximately 70%.
The fact that AstraZeneca's best result was achieved with the formula involving a first half dose has already led to some head-scratching among experts. Many believe this may be due to adenovirus packaging.
Although the vaccine aims to stimulate immune responses against the SARS-CoV-2 spike protein carried by the adenovirus, some immune responses will indeed inevitably attack the adenovirus himself. So if the two-dose approach starts high, the body's defenses may come up with a stronger anti-adenovirus response, rather than focusing on spike proteins. This is of course only speculative. Understanding what is really going on will require a lot more data.
Safety-wise, AstraZeneca has confirmed no serious vaccine-related adverse events . In previous trial results, however, mild side effects of AZD1222 were common, including pain at the injection site, fever, chills, muscle aches and some headaches. Some participants received paracetamol (acetaminophen/Tylenol) as a preventive measure to lessen these effects.
A significant advantage of AstraZeneca's vaccine is that it is relatively easy to scale up . The laboratory pointed out in its press release that it could manufacture up to three billion doses in 2021 , pending regulatory approval. In addition, the vaccine does not require specialized storage conditions . It can in fact be stored, transported and handled under normal refrigerated conditions (2-8°C) for at least six months.
Finally, Le Monde recalls that this vaccine will be sold at cost price for the duration of the epidemic at the price of 2.50 euros per dose in France.
