Hopeful COVID-19 research: Not one but two vaccines show promise

We have been following Prof. Sarah Gilbert and her team’s progress since April 2020, when she told The Times that she is hoping to have a vaccine ready by September. Her team’s vaccine uses a chimp adenovirus that is harmless to humans as a vector.

Since April, the vaccine has shown promise in monkeys and pigs. A couple of weeks ago, we reported that the scientists, from the University of Oxford’s Jenner Institute in the United Kingdom, were recruiting participants for human trials.

Now, the results of the first phase of these clinical trials appear in the journal The Lancet. In the paper, the authors explain that this was a single-blind, randomized controlled trial that took place across five trial centers in the U.K.

The trial included a total of 1,077 healthy participants, all aged 18–55. Of the volunteers, 543 received the vaccine — known technically as ChAdOx1 nCoV-19 but more commonly referred to as the Oxford vaccine, or the AstraZeneca vaccine — and 534 received a control vaccine.

All of the participants who received the Oxford vaccine developed SARS-CoV-2-neutralizing antibodies within 2 weeks. Most of them (32 out of 35) developed them after receiving a single dose.

A group of 10 participants received two doses, and in this group, all developed immune responses. In other words, this phase of the human trial confirmed what the previous trial in pigs had shown: that two doses are better than one.

Furthermore, the vaccine triggered immune responses in T cells, which are key “fighters” in our immune system. These responses peaked 2 weeks after the injection and remained for 2 months. The quantity of antibodies peaked at day 28 and remained for 56 days.

Regarding adverse reactions, the vaccine caused some mild side effects, including “pain, feeling feverish, chills, muscle ache, headache, and malaise.” However, taking acetaminophen preventively eased these side effects.

Study co-author Prof. Andrew Pollard, chief investigator of the Oxford vaccine trial, comments on the findings, saying, “The interim phase I/II data for our coronavirus vaccine show that the vaccine did not lead to any unexpected reactions and had a similar safety profile to previous vaccines of this type.”

“The immune responses observed following vaccination are in line with what we expect will be associated with protection against the SARS-CoV-2 virus, although we must continue with our rigorous clinical trial program to confirm this,” he adds.

“We saw the strongest immune response in participants who received two doses of the vaccine, indicating that this might be a good strategy for vaccination.”

– Prof. Andrew Pollard

Other experts, who were not involved in the research, are also commenting on the results.

For example, Prof. Ian Jones — at the University of Reading in the U.K. — says, “The data from the phase I/II trial of the Oxford vaccine are as good as one could reasonably expect and confirm earlier use of the vector as a general vaccine platform.”

“Trial participants developed the all-important neutralizing antibodies, in most cases after one shot and in all cases after two shots.”

Meanwhile, Prof. Jonathan Ball — at the University of Nottingham in the U.K. — says, “The results of the Oxford chimp adenovirus vaccine candidate show that the vaccine is able to generate antibodies and T cells in humans, and these persisted for several weeks.”

However, he also cautions that much more research is necessary.

“[While] encouraging, there is still a long way to go before we can herald the arrival of a successful coronavirus vaccine.”

– Prof. Jonathan Ball

On this point, experts explain why we should still maintain caution despite the fact that these early results are so encouraging.

Prof. Ball says: “It is unclear whether the levels of immunity can protect against infection — that’s what the larger ongoing phase III trials are designed to test. Nor do we know if this vaccine can protect those most vulnerable to severe COVID-19 disease.”

Prof. Stephen Evans, at the London School of Hygiene and Tropical Medicine in the U.K., also stresses the importance of phase III in the Oxford vaccine trial.

“The key elements required to proceed to a phase III trial are all there,” he acknowledges. “The responses measured in the blood and the absence of serious harms indicate there is a possibility of an effective vaccine against COVID-19.”

However, he adds, “It does not yet show that the disease is reduced or prevented, and this will not be easy to show until phase III trials have been completed in settings where the SARS-CoV-2 virus is circulating at a high rate and people are getting clinical and severe disease.”

The third phase will help establish crucial elements for the success of a vaccine, such as protecting the most vulnerable people and lasting for a longer period of time.

“For the vaccine to be really useful, we not only need the larger studies conducted where COVID-19 is still occurring at a high rate, but we need to be reasonably sure that the protection lasts for a considerable time,” says Prof. Evans. “The results on efficacy have not been presented.”

“It is also vital that those older than 55 (and in this report, three-quarters were aged under 45) are included and the phase II/III trial still ongoing will include such [people]. The authors suggest that this vaccine could work well in [older adults], but we await data to see if this expectation is met.”

– Prof. Stephen Evans

Phase II/III trials are currently ongoing in the U.K., Brazil, and South Africa, and they will also start in the United States.

Experts are also weighing in on the results of a trial led by Chinese-based researchers that tested another vaccine. The results of this trial also appear in the journal The Lancet.

Whereas researchers tested the Oxford vaccine in phase I/II, the Chinese study was a “randomized, double-blind, placebo-controlled, phase II trial.”

Prof. Wei Chen, from the Beijing Institute of Biotechnology in China, is the last and corresponding author of the new paper.

For the trial, Prof. Chen and team enrolled 508 healthy adults, all aged 18 and older. Of these, the researchers assigned 253 to a group that received the vaccine at a higher dose and 129 to a group that received it at a lower dose. A group of 126 participants received a placebo.

Approximately 61% of the participants were aged 18–44 years, 26% were aged 45–54 years, and only 13% were aged 55 years or older.

Here, too, 95% of the participants in the high dose group showed immune responses at day 28 after vaccination, while 91% of participants did so in the lower dose group.

The team notes no serious adverse reactions. Around 1% of the participants in the lower dose group and 9% of those in the higher dose group experienced severe adverse reactions.

The vaccine, called the Ad5-vectored vaccine, “is safe and induced significant immune responses in the majority of recipients after a single immunization,” conclude the paper’s authors.

However, the intervention was less effective in older adults who had “high preexisting anti-Ad5 immunity.”

As Prof. Chen and colleagues write, “In some participants with high preexisting anti-Ad5 immunity, one injection of the vaccine might be inadequate to induce a high level of humoral immune responses, particularly for people aged 55 years.”

Commenting on these findings, Prof. Chen says, “Since [older adults] face a high risk of serious illness and even death associated with COVID-19 infection, they are an important target population for a COVID-19 vaccine.”

“It is possible that an additional dose may be needed in order to induce a stronger immune response in [older adults], but further research is underway to evaluate this.”

Worldwide experts are drawing comparisons between the Oxford vaccine and the Chinese one.

“The […] Chinese study, which uses a human adenovirus instead of the chimpanzee adenovirus, also worked, and despite the difference in the “vector” used, can be considered to [reinforce] the case for an adenovirus vectored vaccine being a viable option for COVID-19.”

– Prof. Ian Jones

Prof. Ball, however, remains skeptical. Echoing Prof. Evans’s previous point about the vaccine helping older adults, he says, “[While] the vaccine trialed in China used a different adenovirus to deliver the coronavirus protein, the fact that the immunity seen in the [older adults] included in the study was much lower than that observed in younger people is telling.”

Several previous studies have suggested that remdesivir, which is a drug that scientists developed for treating Ebola, can reduce the recovery time for people who develop severe COVID-19.

However, the exact action of this broad-spectrum antiviral drug on SARS-CoV-2 remains largely unknown.

For this reason, a team of researchers set out to study it further. Andrea Pruijssers, Ph.D. — from the Vanderbilt University Medical Center in Nashville, TN — is the lead author of the new study.

She explains, “All of the results with remdesivir have been very encouraging, even more so than we would have hoped, but it is still investigational, so it was important to directly demonstrate its activity against SARS-CoV-2 in the lab and in an animal model of disease.”

The research suggests that remdesivir “potently inhibits” the replication of SARS-CoV-2 in human lung cells and epithelial cells in the airways. The researchers also tested the drug in a mouse model of SARS-Cov-2 and found that it successfully reduced viral load and improved the mice’s lung function and health outcomes.

As the researchers write in their paper:

“This is the first rigorous demonstration of potent inhibition of SARS-CoV-2 in continuous and primary human lung cultures and the first study suggesting efficacy of [remdesivir] against SARS-CoV-2 in mice.”

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