Vaccine trial South Africa
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  • The hAd5 T-Cell vaccine for Covid-19 is currently undergoing Phase 1 of its clinical trial, overseen by the University of Cape Town.
  • Like other vaccines, the hAd5 T-Cell jab targets the spike protein on the coronavirus, but goes further to isolate the more stable nucleocapsid protein.
  • This is important in combatting ever-changing Covid-19 variants, like 501Y.V2, which have complex spike protein mutations.
  • The vaccine could enter its final clinical phase at the end of 2021 and may be supplemented by a “booster” in pill form.
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A new clinical trial, overseen by researchers at the University of Cape Town (UCT), is testing the efficacy of a new Covid-19 vaccine with a different approach.

The hAd5 T-Cell vaccine has the promise to protect against current and future variants, including the worrying Sars-CoV-2 501Y.V2  which is most prominent in South Africa.

The first phase of this clinical trial involves administering the vaccine through the Wellcome Centre for Infectious Diseases Research in Africa’s (CIDRI-Africa) Khayelitsha site. This comes after the South African Health Products Regulatory Authority (Sahpra) recently gave hAd5 T-cell producers, ImmunityBio, the go-ahead to begin its clinical trial.

ImmunityBio is also trialling an oral "booster" version of the T-cell vaccine in the US. If these tests are successful, the T-cell vaccine could be administered as a supplementary “booster” in pill form and combined with other vaccines to offer better protection.Based on what it called "encouraging results" in tests on animals, "the potential for our second-generation T-cell vaccine to serve as a ‘universal boost’ to the vaccines to be deployed in South Africa is exciting,” said ImmunityBio’s chairperson and chief executive, Patrick Soon-Shiong.

But Graeme Meintjes, the second chair in the department of medicine at UCT, warned that the hAd5 T-Cell vaccine, while promising, does not provide an immediate solution to South Africa’s Covid-19 outbreak. Should the vaccine pass its first clinical trial, two more phases remain.

The third phase, which includes thousands of participants, is only likely to conclude at the end of 2021 and depends on the outcomes of the first two smaller-scale trials. There is, however, reason to be optimistic in the interim.

“A safe and universally effective Covid-19 vaccine that is easily accessible is critical for South Africa at this point in the pandemic,” says Morena Makhoana, CEO of the Biovac Institute, the bio-pharmaceutical company charged with overseeing the storage, delivery, and, potentially, the production of the vaccine.

“We believe that this Phase 1 trial is a crucial step for the country in this regard and are eager to see the outcomes of the trial.”

Unlike other Covid-19 vaccines which are currently being administered globally and aim to generate immunity against the SARS-CoV-2 spike protein,  the hAd5 T-Cell vaccine targets the more stable nucleocapsid protein.

It is administered as two jabs, three weeks apart.

SARS-CoV-2: Spike proteins vs nucleocapsid protein

Most Covid-19 vaccines - including Oxford/AstraZeneca, Pfizer/BioNTech and Moderna - target the coronavirus' spike protein. This spike protein is the part of the virus which allows it to enter cells within the human body. 

But the spike protein is prone to mutations which not only make the virus' variants more transmissable - like 501Y.V2, which current studies suggests is at least 50% more infectious - but may also decreases the efficacy of some vaccines.

The nucleocapsid protein, which forms the inner part of the coronavirus wrapped in its RNA, is more stable and less likely to mutate. This means that vaccines which target both the nucleocapsid protein and spike protein are thought more likely to be effective against current and future variants. 

An increasing concern among researchers is the rapid mutation of the coronavirus spike protein, which may make it more difficult for current vaccines to provide stable immunity. This setback was recently realised during testing of the Oxford-AstraZeneca jab, which was to underpin South Africa’s vaccine rollout.

While the initial trial of the Oxford-AstraZeneca vaccine in mid-2020 was proven to have 75% efficacy, this drops to 22% against the 501Y.V2 mutation in SA, which was first identified in August. This particular variant is responsible for more than 90% of the country’s Covid-19 cases.

As a result, the rollout of Oxford-AstraZeneca vaccines was put on hold and replaced with Johnson & Johnson jabs.

Other vaccines which target the spike protein are likely to experience varying degrees of decreasing efficacy within the context of 501Y.V2.

The coronavirus’ inner nucleocapsid protein has not been prone to major mutations, and so may be a more reliable target for vaccines across variants.

“This Phase 1 clinical trial will be assessing a vaccine candidate that concurrently exposes the immune system to both the spike and nucleocapsid proteins. The dual construct of the hAd5 vaccine candidate has the potential to provide recipients with durable, long-term immunity induced by memory T cells and memory B cells against SARS-CoV-2, including current and any future variants," says Meintjes.

"This potentially includes immunity against the 501Y.V2 variant, which has been found in patients in South Africa and elsewhere.”

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