The reason is that, with the virus raging along with uncertainty about vaccine supply, vaccinating more people with a single dose would be more effective in preventing deaths and hospitalizations than if fewer people received two doses. However, critics question the advisability of moving away from the timetable tested during clinical trials. Here are five things to know about the evidence and the possible implications of delaying vaccine doses.
1. There is little trial evidence to show the impact this will have on the Pfizer / BioNTech vaccine.
When UK officials announced the new guidelines, two vaccines had been authorized for use. The first vaccine, from Pfizer / BioNTech and now rolling out across Europe, uses a new technology that introduces genetic material, called mRNA, which contains the instructions to produce the so-called coronavirus spike protein in the body to elicit a response. immune. Two weeks after the second dose, the vaccine showed a spectacular 95% efficacy.
The trials for this vaccine did not test different dose gaps, nor did they assess the impact of one dose versus two. In a peer-reviewed study, the companies showed that the vaccine’s efficacy was 52.4% between the first and second doses, which were 21 days apart. However, UK officials suggested that in the trial most of the ‘vaccine failures’, in which people contracted Covid-19 despite being vaccinated, occurred in the period shortly after the first dose. Between day 15 and 21, the observed efficacy against symptomatic Covid-19 was estimated at 89%, leading officials to conclude that “the short-term protection of dose 1 is very high as of day 14 after vaccination “.
But scientists have stressed that levels of so-called neutralizing antibodies, which immunologists say are the most formidable weapons in the immune arsenal, appear to rise dramatically only after the second dose. Meanwhile, the companies themselves issued a statement saying: “There is no data to show that protection after the first dose is maintained after 21 days.”
2. Is there any evidence that delaying the second dose of the Oxford / AstraZeneca vaccine might be beneficial?
The second vaccine, made by Oxford / AstraZeneca, is based on a technology that has been used successfully before: a harmless chimpanzee cold virus modified to carry genetic material that contains the instructions for the spike protein . Clinical studies evaluating the Oxford-AstraZeneca vaccine included spacing doses two to three months apart, which appeared to trigger a stronger immune response. But the data were taken from a small subset of patients who received half a dose plus a full dose, compared to the majority of participants who received two standard doses a few weeks apart.
The data for the two standard doses showed an overall efficacy of 62%. But a dosing error that gave a subset of clinical trial participants half a dose followed by a full dose actually boosted efficacy to 90%. The numbers in the patient subset were received with cautious optimism, due to the small number of patients and because no patient was over 55 years of age. However, the UK health regulator suggested that the higher efficacy of the half-dose / full-dose regimen was due more to a longer time interval between doses, rather than the regimen. The agency conducted an exploratory analysis estimating the efficacy against symptomatic Covid-19 of 73% after the first dose.
3. Different vaccines may need different approaches.
Dr. Mariola Fotin-Mleczek, chief technology officer at CureVac, a German company in the late stages of developing its own Covid-19 mRNA vaccine, says she was skeptical about using a one-size-fits-all approach. vaccines with different mechanisms of action. . For mRNA vaccines like the CureVac candidate (and the Pfizer / BioNTech product), the first dose primes the immune system, but the immune response is not fully established, he says. “Without increasing it in the next few weeks, the antibody responses decrease even more. Therefore, you need to test what the impact on protection would be.
Currently, there is a lack of data on whether protection will persist, “he said. The World Health Organization appears to agree with this analysis, suggesting that while there is some data to support delaying doses of the Oxford / AstraZeneca vaccine, there is no Scientific evidence to extend the second dose of the Pfizer / BioNTech vaccine to 12 weeks.
4. It is feared that weaker protection could accelerate vaccine-resistant mutations in the virus, but scientists are divided
Although it is not known how protective a single long-term injection is, it is also unclear how long the protection of two doses is. The effect of either vaccine in thwarting viral transmission is also inconclusive. However, scientists have expressed concern that a weak response to the virus in people who have received the first dose could accelerate the virus’s ability to develop vaccine-resistant mutations.
“My concern, as a virologist, is that if you wanted to make a vaccine resistant strain, what you would do is build a cohort of partially immunized individuals in the teeth of a highly prevalent viral infection,” said Paul Bieniasz of Rockefeller University. STAT News. Other scientists think the threat of that happening is small on the grounds that the virus would have a hard time undermining the complex antibody responses generated by vaccines.
5. Delaying doses could undermine compliance with other vaccination schedules.
Although it is understandable why governments would delay the second dose in an emergency situation, it is not good for the broader environment to build trust in vaccines and science, says Professor Heidi Larson, founding director of the Vaccine Confidence Project in London. School of Hygiene. And Tropical Medicine, UK. One of the biggest concerns parents have about vaccines is scheduling: They often wonder if it is possible to space vaccines due to the perception that their child’s immune system could become overloaded, says Professor Larson.
The explanation given is that it is important to stick to the schedule because that is the way vaccines are most effective, she notes, noting that this decision therefore breaks the trust that scientists like her have been trying to foster. in the scientific process. “It just gives the public the feeling that they tell us one thing and then they go and do, what we have been telling parents that they cannot do, which is to change the schedule,” he said, adding that this decision has implications for confidence in vaccines well beyond the current pandemic.
“This is a hugely historic moment for many reasons, and this will not be forgotten. So don’t just think about the emergency think about the implications for confidence and post-Covid rebuilding. “
Original article
This article was originally published in Horizon, the EU Research and Innovation Magazine
