Moncef Slaoui is the scientific head of Operation Warp Speed, the U.S. government’s initiative to accelerate the development of vaccines and therapeutics for COVID-19. He is a leading expert on vaccine development, having headed GSK’s vaccine program for 30 years before retiring in 2017. HVP Editor Kristen Jill Abboud recently spoke with Slaoui on the eve of the U.S. Food and Drug Administration’s (FDA) meeting with an independent advisory board of experts at which they will consider granting an Emergency Use Authorization for Pfizer/BioNTech’s COVID-19 vaccine.

An edited version of the conversation appears below.

As soon as tomorrow, we could have the first COVID-19 vaccine authorized in the U.S. Once authorized, how quickly will this vaccine make it to those in the highest priority groups?

First, I think it is very likely that this vaccine will receive authorization. The FDA comments on the Pfizer/BioNTech file and all the data are very clear and very supportive, so the expectation is that there will be an approval. Within 24 hours of the approval, vaccine doses will be already arriving at the immunization sites that various state health agencies have identified for us, and probably within 24 hours of that, the first people will be immunized.

There have been some manufacturing issues reported for Pfizer/BioNTech’s mRNA vaccine. Will this affect the number of vaccine doses immediately available?

I think this is really the normal course of things as you ramp up manufacturing—you always have to go through a learning curve to determine how the ramped-up manufacturing cadence can be optimized. Availability of raw materials is a potentially limiting factor, but these things are all under control, and as far as the U.S. government is concerned, there is no issue with manufacturing. Pfizer/BioNTech made a commitment in September for the number of doses they can deliver and that is the number of doses we will receive.

The mRNA vaccines must be stored at freezing temperatures because of stability issues. Are there any manufacturing issues particular to mRNA vaccines due to their relative instability?

Stability is not an issue, it’s more sourcing of raw materials and just the process of scaling up. There is no intrinsic process development issue. Normally vaccines are never launched as they are manufactured. For any biologic product, you have a learning curve as you ramp up manufacturing, so you typically build up a stock and then you launch because this allows you to manage the ebb and flow.

The FDA is also scheduled to consider an Emergency Use Authorization (EUA) for Moderna’s mRNA vaccine. After that, what are the next vaccines supported by Operation Warp Speed that will move forward for authorization?

Moderna’s vaccine will be reviewed on December 17th and I can tell you the FDA will most likely reach the same conclusion they will reach with the Pfizer vaccine because the data are remarkably similar. After that, the next vaccine in line is the Janssen/Johnson & Johnson candidate. There are two Phase III trials for this vaccine. One Phase III trial is a one-shot regimen and the other is a two-shot use of the vaccine. Recruitment is almost complete in the one-shot trial—we have maybe 38,000 subjects enrolled by this morning and we plan to complete recruitment by the end of this week. Then it will just be a matter of further accretion of endpoints in the trial, and given the strength of the pandemic, I wouldn’t be surprised if it is in very early January that there is an announcement on the outcome of the trial.

I am very optimistic that even though it is a one dose vaccine it may achieve very high efficacy. In the Pfizer data, if you look into the immune response after one dose of the vaccine, there are barely detectable levels of neutralizing antibodies. There is a much better response after the second dose. However, as of 14 days after the first dose of vaccine, there are no more cases of COVID in the vaccine group, whereas cases accumulate in the placebo group. If you compute cases from day zero, there is already 50% efficacy after one dose of the Pfizer vaccine, so I’m very optimistic that one dose of the Johnson & Johnson vaccine will work. We wanted to have something else that would be a breakthrough in addition to the mRNA in terms of ease of distribution and inoculation because ultimately that’s what counts. And clearly, giving two shots is more complex than giving one shot because you will always have people who do not come back for the second dose and the cost and complexity of giving one dose is so much lower. We are confident that the Janssen vaccine will have its efficacy data early in January and the median two-month follow up for safety is going to be somewhere at the end of January, which means that this is around the time that the EUA could be applied for. Our hope is that this vaccine would receive an EUA in the first half of February. We are already stockpiling vaccine doses, and as soon as it is authorized it will contribute significantly to our ability to immunize people.

After that, there is the AstraZeneca vaccine. The data for this vaccine is more complex to interpret if one looks at the U.K. and Brazil trials, with their differential outcomes and dosages, etc. [see recently published data]. However, we are waiting for results from a totally independent Phase III trial going on in the U.S. with Operation Warp Speed oversight. That trial has now recruited more than 17,000 subjects and is aiming to recruit 30,000—though we may stop at 25,000 participants because the attack rate is so high in the population. That trial should be complete in late January or early February, and if data are favorable, we could probably expect an application for authorization in late February/early March. We are also stockpiling doses of this vaccine.

Is the U.S. trial testing the two, full-dose regimen?

The U.S. trial is the normal two, full-dose immunization schedule. There is no scientific rationale for a lower first dose and a higher second dose.

Given the positive response after just one dose of the Pfizer/BioNTech vaccine, is immunizing with one dose being considered so you can vaccinate twice as many people?

It is, of course, considered but one would have to study it in a real trial because with that vaccine we observed that level of efficacy just over three or four weeks until the second dose was given. We would need to run new trials to confirm the persistence of that level of protection with that mRNA vaccine. Where we are really studying this is with the Johnson & Johnson vaccine.

Did the efficacy data we’ve seen so far surpass your expectations?

Well, yes, although I was expecting high efficacy. I was saying we could expect 80-90% efficacy and I remember that when I said that in June, most people said that was impossible or highly unlikely. I never would have predicted 95% or even 100% efficacy against severe disease, so the efficacy is better than I expected.

This virus, from a virological standpoint, is relatively weak. Most people have asymptomatic infection. It’s really when your immune response has trouble firing up and is really slow early on that you get in trouble because then you get very significant viral replication, and when then the immune response finally comes up it is highly disruptive. That’s when you get disease. Vaccination is enough to dramatically accelerate the pace of the immune response, so I think just priming the immune system, as we say, is enough, and that is what the one-shot vaccine data suggest, which is one of the reasons we went ahead and tested a one-shot vaccine. I expect these vaccines to all be highly effective and that immunity will be long lasting.

With highly effective vaccines in hand, is the next biggest battle getting people to actually take them?

Absolutely. I think this is the biggest problem. Vaccine isn’t the objective; the objective is vaccination. Having vaccines on a shelf is useless. It is key that we work to engage the population that is hesitant and allow them to see the data, understand the data, and to see how we went so fast so that they will realize that we haven’t actually cut any corners and that the data supports that these are very effective and very safe vaccines. Hopefully, this will change people’s minds. It’s definitely helpful that the vaccine efficacy is 95%. You can already see the movement in various surveys which show that people are more accepting than they were before. Of course, there will always be those who are anti-vaxxers.

The word unprecedented is probably overused but the pace at which COVID vaccine development has occurred is really unprecedented, right? How would you characterize the scientific process and the role Operation Warp Speed has played in driving such fast progress?

The reason this went very fast is that there were a few decades of R&D, scientific innovation, and breakthroughs in academia, biotech companies, and industry working on the platform technologies being used. That’s really why things went so fast. Messenger RNA is a pure platform—it is 100% the same product in terms of chemical composition whether you have a vaccine against COVID, flu, herpes, or hepatitis. All of the work on that platform over the last 10 years to understand the toxicology, the clinical expectation of safety, and the manufacturing strategy was all relevant to the COVID-19 vaccine because it involves the same processes.

Similarly, the work that was done with SARS-CoV-1 and MERS [Middle East Respiratory Syndrome] also helped scientists immediately identify the sequence of the Spike protein of SARS-CoV-2 and show that it was the right target for vaccine development. As a result, this very upstream part of the R&D process took weeks rather than years. This was possible because we were building on the historic work of academia and biotech and pharma companies.

In addition to that, Operation Warp Speed has really enabled enormous acceleration through financial and operational risk taking. We prepared all the clinical trial conduct, recruited the sites, and conducted all the activities required to test these products in Phase III trials while the technical work was still being done. We were ready to go every step of the way. If the Phase I trial results had been negative, we would have spent $500 million preparing for the Phase III trials for nothing—no company ever does that. That is a huge accelerator on the clinical side. The size of the trials also helped to accelerate things because we were able to accrue more cases faster and achieve the endpoint faster.

Likewise, on the manufacturing side, we geared up and scaled up manufacturing sites and started manufacturing vaccine when the Phase III trials were starting. That’s why we have millions of doses of vaccine stockpiled when the Phase III trials just reported efficacy results. So, I would say that this effort was really possible because of a combination of applying the great science that was done before, taking huge operational, logistical, and financial risks, and utilizing the capabilities of the U.S. Department of Defense.

Interview by Kristen Jill Abboud