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It is a pragmatic solution to an incredibly urgent problem: how to immunize large numbers of people at risk of a rampant variant of Covid-19 in the shortest time possible. The answer that government advisers have found is to give everyone, more than 20 million of them, a single shot of the Oxford / AstraZeneca vaccine so they have some protection and postpone the second dose to three months later, when expected there will be plenty of vaccine available for boosters.
The approval of the Oxford / AstraZeneca vaccine by the Medicines and Healthcare Products Regulatory Authority (MHRA) has been met with great enthusiasm and acclaim, rightly so, because the inexpensive and easy-to-use vaccine could help end the pandemic everywhere the world.
But as the United Kingdom prepares to launch millions of first injections of the vaccine, ahead of Europe and the United States, who seek more data, questions are already being asked about how it will be used.
It’s not about security. All experts agree that this is a safe vaccine. But the MHRA, along with expert government advisers in the Joint Committee on Vaccination and Immunization, have come as a big surprise by endorsing two injections up to 12 weeks apart for not just the Oxford / AstraZeneca vaccine but also the Pfizer / vaccine. BioNTech which is already in force. use.
This program was not the one that was tested, as Pfizer / BioNTech immediately pointed out. Their final phase 3 trial showed that people began to be protected 12 days after a vaccine, but almost all received two injections in three weeks. “There is no data to show that protection after the first dose is maintained after 21 days,” the company said.
The MHRA and JCVI appear to be extrapolating data from a small subset of people who participated in the Oxford / AstraZeneca trial in the UK. It is famous that in this group of less than 3,000 people (and for the scale, Pfizer / BioNTech did an international trial with 43,000 people) the efficacy was 90%.
This was due to an inadvertent error. The first dose they were given was half a dose. That seemed to work better than two full doses, which was 62% effective in a trial of more than 11,000 people.
But now the MHRA has discarded that explanation and presented a different one. In that small group, many people received their second injection later than usual, up to 26 weeks later in some cases. But in those who had it at 12 weeks, the efficacy reached 70%.
Professor Andrew Pollard, in an interview with The Guardian, said it was not surprising. “If you have a longer gap between the first and second doses, then the force of the boost tends to be stronger. So that’s not a surprise or unusual. That’s what we see with almost every other vaccine that has been tested. “
But the shifting interpretation of what was happening adds to the sense of confusion. And there are other questions. What if you wait more than 12 weeks for the second injection? Are people less likely to go ahead and get their second dose after three months of feeling pretty well protected? For the Pfizer / BioNTech vaccine, what if there are not enough supplies to give people a second injection? That vaccine has been approved in Europe and the US and is in demand all over the world.
The UK is once again the first to emerge from the traps and will find the answers to these questions for itself. Neither the United States nor Europe is rushing to evaluate the Oxford / AstraZeneca vaccine. The US Food and Drug Administration is awaiting the results of ongoing trials there, which should also answer another important question for which there is limited data: how well it works in the elderly.
The European Medicines Agency says it is also evaluating “evidence on its efficacy and safety from various ongoing clinical trials” and pondering the answers to the questions it asked AstraZeneca over Christmas.
There is no question that Oxford / AstraZeneca’s is a good vaccine that is desperately needed. Critically, Pollard said, “since three weeks after the first dose, we have not seen anyone who has been vaccinated admitted to the hospital or who develops a serious illness.” But you need to answer the questions and you have to be very careful about how vaccines are used so that the public has the confidence in them that we all need to end the pandemic.
