Two More COVID-19 Vaccine Candidates Show Promise In Peer-Reviewed Clinical Trial Results
Credit: Jernej Furman

In the largest and perhaps most robust peer-reviewed study to date, A COVID-19 vaccine candidate developed by pharma giant AstraZeneca and Oxford University has been shown to induce strong antibody and T cell responses in healthy volunteers, according to Phase 1/2 trial results published in The Lancet on Monday.

Most studies so far have focused on measuring the level of neutralizing antibodies, or antibodies that can bind to the virus in the blood to prevent it from attacking human cells. However, the Oxford/AstraZeneca vaccine was also able to to induce another type of immune response in a subset of 43 healthy volunteers within 14 days of vaccine – a T-cell response, which is another specialized immune response that can attack cells infected with the virus.

The immune system has two ways of finding and attacking pathogens – antibody and T cell responses. This vaccine is intended to induce both, so it can attack the virus when it’s circulating in the body, as well as attacking infected cells,” said study lead author and Oxford professor Andrew Pollard in a press release. “We hope this means the immune system will remember the virus, so that our vaccine will protect people for an extended period.”

However, “there is still much work to be done before we can confirm if our vaccine will help manage the COVID-19 pandemic, but these early results hold promise,” added co-author on the study and Oxford professor, Sarah Gilbert.

WHO Health Emergencies Executive Director Mike Ryan shared the same sentiment.

“This is a positive result but again there’s a long way to go. These are Phase I studies; we now need to move into larger scale real world trials, but it is good to see more data,” Ryan told reporters on Monday.

The Oxford/AstraZeneca group tested their vaccine in 1,077 healthy volunteers, making the trial many times larger that of Moderna, which tested their vaccine candidates in only 45 healthy volunteers in Phase I trials. Moderna’s vaccine candidate, developed in collaboration with the US National Institute of Allergies and Infectious Diseases, was the first to have Phase I results released in a peer reviewed journal.

A third COVID-19 vaccine candidate, developed by Chinese biopharma company CanSino Biologics Inc. and the Chinese Academy of Military Sciences, was also able to induce an immune response in a Phase 2 trial that enrolled over 500 healthy volunteers, according to results published in The Lancet on Monday.

However, researchers have previously expressed concerns about the Ad5 vector, the technology used to carry the vaccine, in the CanSino candidate. HIV vaccine candidates using the Ad5 vector had inadvertently increased the risk of HIV infection in previous trials, and it is unknown whether the CanSino COVID-19 vaccine may have similar effects.

While early Phase clinical trail results have shown to be able to induce an immune response in healthy volunteers, it’s still too early to tell whether that immune response will protect against coronavirus infection or disease.

All three vaccine candidates are preparing to enter the final and largest phase of the vaccine testing process, Phase III clinical trials. These massive trials will enroll tens of thousands of volunteers in all age groups in order to test whether the vaccines can protect against infection by the virus and symptomatic COVID-19 disease.

AstraZeneca/Oxford Vaccine Candidate Set to Move Into Multi-Country Phase III Trials

Colorized electron microscope image of SARS-CoV-2, the virus that causes COVID-19

While the Phase 1/2 trial is ongoing, the AstraZeneca/Oxford vaccine, ChAdOx1, will move into further Phase 2 and Phase 3 trials. AstraZeneca has already ordered 100 million doses to be produced by the Serum Institute of India, a major developing world biopharma company and generics producer, for Phase 3 trials.

Volunteers are currently being enrolled in the UK, Brazil, and South Africa, making this the first vaccine candidate to be tested on the African continent.

The authors further noted that the Phase III trial will focus on observing the vaccine in a wider demographic, including those at higher risk of COVID-19 infection or death such as older people, ethnic minorities or marginalized people, people with preexisting health conditions, and healthcare workers. Participants in the earlier Phase 1/2 trial were mostly likely to be young and Caucasian – some 91% of study subjects were white and the average age of participants was 35 years.

None of the participants reported serious adverse reactions to the vaccine. Around 70% of the participants who received ChAdOx1 reported mild adverse side effects such as fatigue and headache, compared to 48% in those who received the placebo meningitis vaccine.

Participants who took paracetamol, a pain common pain medication, at the time of injection had a reduced likelihood of experiencing adverse side effects. Paracetamol had no effect on the immune response generated by the vaccine.

WHO Experts Urge Countries To Step Up Contact Tracing Rather Than Waiting For Vaccine

WHO Assistant Director-General of Emergency Response, Ibrahima Socé Fall

Still, WHO experts on Monday warned against waiting for an effective vaccine to stem the tide of the pandemic, urging countries to step up contact tracing efforts.

“We do not have to wait for a vaccine. We have to save lives now,” said WHO Director-General Dr Tedros Adhanom Ghebreyesus. “Contact tracing has long been the bedrock of outbreak response from smallpox to polio to Ebola, and now COVID-19.”

“If we look at viruses that are much more fatal than COVID-19, we were able manage and master these epidemics by regularly following [contacts] with high level efficiency,” said WHO Assistant Director-General of Emergency Response, Ibrahima Socé Fall. The 2014-2016 Ebola outbreak in West Africa for example, was largely managed and quashed through contact tracing, before a vaccine was available.

Investing in contact tracing now is even more important, considering “many countries were not very well prepared for contact tracing” at the beginning of the pandemic, according to Fall.

“Developed countries have surveillance systems centered on hospitals, but by the time the patients arrive it’s too late. They’ve already contaminated others in the community,” said Fall.

“Nothing replaces boots on the ground,”  said Dr Tedros. “[Countries must] train workers to go door to door to find cases and contacts, and break the chains of transmission.”

Image Credits: Flickr: Jernej Furman, National Institute of Allergy and Infectious Diseases, NIH.