While Pfizer and BioNTech expect enough safety data by late November to seek an emergency approval for their Covid-19 vaccine in the US, two obvious limiting factors make a quick scale up and rollout difficult — the task of ensuring each recipient gets two jabs exactly three weeks apart, and arranging the cryogenic logistical distribution network.
Besides this, four other potential limiting factors emerge from the early information released yesterday from their phase 3 human trials of the vaccine: does it prevent infectiousness–analysts point to the possibility that it could stop someone from getting Covid-19 symptoms, but not from spreading it to others — and does it work well in high-risk groups like the elderly?
Most importantly — how long does the immunity it provides last? While more clarity on the vaccine would emerge as the late-stage trial progresses, this question could potentially take months–even years–to answer.
Global stock markets reacted strongly to the interim data released by Pfizer on Monday–of 94 participants, the vaccine was “more than” 90 percent effective in preventing Covid-19 among those who had received two doses. However, the caveat here is these shots will need to be kept in ultra-cold storage.
“Initially, our potential COVID-19 vaccine will need to be stored at -75°C±15°C,” a Pfizer spokesperson told The Indian Express. This means beefing up existing freezer capacities to hold millions of doses at temperatures between -90°C to -60°C–something that, according to experts, no country has really been prepared for.
“These vaccines are going to be expensive and their storage and delivery will be a challenge,” said vaccine scientist and Christian Medical College, Vellore professor Dr Gagandeep Kang.
“This is a speciality requirement, which very few pharma companies have in a small capacity,” said Sunil Nair, CEO, Snowman Logistics, which has been studying the possibility of upgrading its current cold chain capacities in the country to such cryogenic levels.
According to him, the general capacity of existing cold storage warehouses in India can store anywhere between 4-5 crore doses of a vaccine. “The (sub-zero) units that we have heard of pharma companies using can store maybe 25,000-30,000 doses,” he added.
While it is learnt that Pfizer makes its own dry ice and that it has tie-ups with companies like FedEx and UPS, which have the logistical abilities to supply medicines at ultra-low temperatures, this sophisticated supply network is largely restricted to developed markets. The availability of dry ice supplies and logistical capabilities to transport and maintain the vaccine at such temperatures could be a limiting factor in a place such as India.
“A lot of India’s cold chain capacity (for its universal immunisation programme) was dependent on the polio vaccine, which requires -20°C long-term storage, and then 2°C to 8°C (when distributing for vaccinations). This requires -80°C, which uses two compressors instead of -20°C, which uses one, and the amount of electricity used to run them is much greater too. For a country like ours, where electricity is a problem, just ramping up refrigeration capacity for a vaccine like this will not be enough,” said Dr Kang.
It comes as little surprise then that, while Pfizer has arrangements with some governments in the west to supply limited doses of the vaccine, most Asian and African countries are more inclined to handle a vaccine that can be stored closer to room temperature.
In fact, the Indian government’s thinking so far on ramping up cold chain capacities doesn’t prioritise vaccines requiring sub-zero storage temperatures.
“Augmented capacities would not have sub-zero temperatures, because we still feel that eventually we may not require such vaccines in large quantities. We may not require them at all,” said a senior government official in the know of the centre’s evolving strategy to vaccinate priority groups by July 2021.
The data presented from the trials – in US, Germany, Brazil, Argentina, South Africa and Turkey – is not a final analysis as it is based on only the first 94 volunteers, warn some experts. The effectiveness metric for the vaccine may be subject to changes when the full results are analysed, they feel.
“On the first hand, this is interim data…from the 44,000 (participant) study done by Pfizer in the United States. We know from previous vaccine experiences that vaccine efficacy can vary a lot from country to country, from population to population and the big surprise comes when you take people from high income countries and compare them with middle- to low-income countries,” said Massachusetts-based vaccine expert Dr Davinder Gill. “It was 90 percent efficacy in the US, but what was it in Brazil, or South Africa? I think, until that comes out, there will still be that question of how effective this vaccine is across multiple populations, different demographics, ethnic groups and genders.”
The two companies say they will be able to supply 50 million doses by the end of this year and around 1.3 billion by the end of 2021. Each person needs two doses. Which translates into 25 million people in the remaining days of this year and 650 million people next year.
The vaccine uses a completely experimental mRNA approach, which involves injecting part of the virus’s genetic code – in order to sensitise the immune system. Previous trials have shown the vaccine trains the body to make both antibodies, as well as T-cells, to fight the coronavirus.
“This (mRNA) is a new technology and these vaccines are going to be manufactured very carefully for stability, because one of the big issues with RNA vaccines is stability,” said Dr Kang.
“We now have proof of principle that the vaccine, which is based on expression of the spike protein (the spiky outer layer of the SARS-CoV-2 virus), works. That means that it’s even more likely that other vaccines based on the spike protein may also work,” she said. “My thinking is we should wait until we have a spike protein vaccine that fits our delivery capacity, which would make things at least a little less complicated…rather than looking at one successful vaccine and trying to fix our delivery system around it so that everyone can get it,” she added.
All the limitations notwithstanding, the big advantage of the mRNA approach, which has never been shown to work in humans before, is that the data gathered from the large-scale trials mean the firms can quickly and easily make minor revisions to the mRNA sequence, thus tweaking the proteins the body develops immunity to. This means that if new strains of the virus were to emerge, changes to the vaccine could be done rapidly to adapt to the viral mutations.
While the vaccine, labelled BNT162b2, has been tested on over 43,500 people in six countries and “no safety concerns” have been raised, the latest details issued by the developers leave a question mark on whether the vaccine prevents infectiousness, besides the need for clarity over its long-term efficacy and effectiveness in key vulnerable groups, such as the elderly. The Oxford-AstraZeneca vaccine is already known to stimulate a good immune response in the elderly.
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