The latest news on a leading Covid vaccine candidate is promising, but how optimistic should we be?

  • Latest results from Pfizer's Covid-19 Phase 3 vaccine trials have sparked cautious excitement in the global race.
  • Pfizer told Health24 it was committed to working with governments to supply equitable access to the vaccine when it gained regulatory approval.
  • But while the results were encouraging, there were still certain significant hurdles to overcome, two experts told Health24.

Drug maker Pfizer said on Monday data from their Phase 3 experimental Covid-19 vaccine, BNT162b2, showed it was 90% effective in preventing infections in volunteers.

The company and its collaborator, BioNTech, stated no serious safety concerns were found during their large-scale global clinical trials, and they expected to seek US authorisation this month for emergency use of the vaccine.

The data released was based on global data that included the trial site in South Africa, a Pfizer spokesperson told Health24.

"We are pleased to share that the trial in South Africa is going as planned, having already completed recruitment of participants across four sites in Gauteng, Limpopo and the Western Cape," the company said.

While there are still some unanswered questions, such as how long the vaccine will provide protection, international scientists have welcomed the news saying it "is an excellent result for a first generation vaccine".

Health24 asked two local experts, Professor Wolfgang Preiser, head of the division of medical virology at the University of Stellenbosch, and Professor Thomas Scriba, deputy director of immunology and laboratory director at the South African Tuberculosis Vaccine Initiative, University of Cape Town, whether this was finally a light at the end of the tunnel of the Covid-19 pandemic.

'Results may mean a breakthrough for other infectious diseases'

According to Preiser, the results were positive, considering the US Food and Drug Administration (FDA) expected at least 50% efficacy from any Covid-19 vaccine.

"However, I would not dare make a full assessment until the data is fully published," he said.

"The number of people infected was less than 100, so statistically there is surely a wide-span still. We also do not know anything more specific, such as its effectiveness in different age and risk groups.

“It may be a signal that other vaccines that elicit immune responses to the same viral proteins as this one might also work, even if they achieve this immune response in very different ways."

Preiser added if all this held true, it would be amazing news as this would be the first mRNA vaccine to be successful in human beings. "It may mean a breakthrough for other infectious diseases, too."

'Good news, but let's wait for analysis of results'

Scriba also praised the results in that vaccine efficacy of 90% was a high level, adding if a similar level of efficacy was found upon completion of the trials, and there were no serious safety concerns that were raised, it would be good news for this vaccine candidate and, overall, vaccination against Covid-19.

However, he cautioned: "It should be noted that this was a press release of an interim analysis of results from early stages of the trial and not a scientific publication that has gone through peer review.

"The latter allows true scrutiny of the results, which is important because every clinical trial is subject to certain limitations, interpretation nuances and complications, and information about these is currently not available.

"The result is also from the period between the first vaccination and seven days after the second vaccination, a total period of 28 days. It does not tell us anything about the durability of the protective response," Scriba explained.

A key attribute of a highly effective vaccine, he said, is that it provides protection against infection or disease for a long period, preferably many years, so that people do not have to be vaccinated repeatedly.

"Some of the most effective vaccines, such as measles vaccine for example, protect vaccinated individuals for decades, so it will be important to see what the efficacy results look like for much longer follow-up periods than 28 days," he said.

The importance of distribution networks and vaccination programmes

One also has to bear in mind certain challenges, if and when the vaccine became available to the public, Scriba added.

He said once a vaccine was licenced for human use by regulators, it would need to be manufactured in large volumes, and distribution networks needed to be established and vaccination programmes would have to be put in place to deliver the vaccine to those who needed it.

"These are all non-trivial endeavours. 

"We have had highly efficacious vaccines for a number of deadly diseases for decades and yet these diseases are still causing many deaths and cases of disease because these vaccines do not reach all those who need them.

"This result is clearly an important and very positive first step in a chain of many steps that need to be taken before vaccine vials are available in pharmacies and clinics." 

Certain groups should be prioritised: Pfizer 

Pfizer's news release stated that based on current projections, the company expected to produce globally up to 50 million vaccine doses in 2020 and up to 1.3 billion in 2021.

Its spokesperson told Health24 it had already started manufacturing the vaccine, and that, if the vaccine candidate was successful, the available 50 million doses would be allocated proportionally across the countries where they have fully executed supply agreements (that includes delivery of a portion of doses in 2020).

"The allocation of doses to the appropriate populations within a country is a decision for local governments based on relevant health authority guidance. 

"In line with our commitment to equitable access, we have reached out to governments across sub-Saharan Africa, including South Africa, to understand how we can support their Covid-19 vaccines strategy.

"We are committed to working collaboratively with governments and other stakeholders, as appropriate, to supply the world as quickly as we can, together, but believe that frontline healthcare workers, essential workers, immune-compromised individuals, nursing homes, and public safety officials should be prioritised consistent with global public health guidelines," the company said.

Logistical hurdles to consider

Preiser pointed to the hurdles involved in the transportation and distribution of this particular vaccine.

Unlike the adenovirus vaccines (such as the Johnson & Johnson vaccine candidate currently in clinical trials), the transport and storage requirements of this vaccine candidate has a freezing requirement of minus 70 degrees Celsius or below, which will make the distribution of it challenging, especially to places without advanced medical facilities.

Pfizer's vaccine also requires two jabs given a few weeks apart, which could be another significant logistical hurdle.

"It will take many months still until enough doses of the vaccine become available to vaccinate a substantial proportion of people, starting hopefully with those at highest risk.

"To summarise, this is great news. This is a light at the end of the tunnel, but the tunnel is still very long and the light quite small still," Preiser said.

READ | Leading Covid-19 vaccine candidate 90% effective in Phase 3 trial

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