NEW YORK (REUTERS) - Wealthy governments are looking to Covid-19 shots from Pfizer and Moderna to keep their vaccination programmes on track, as safety concerns and production problems sideline vaccines from AstraZeneca and Johnson & Johnson (J&J), public health experts and industry analysts say.
Countries in Europe and Asia, as well as South Africa, are limiting or halting use of AstraZeneca's shot over safety concerns. Roll-out of J&J's one-shot vaccine was paused in the United States and Europe this week over a handful of cases of very rare but dangerous blood clots in the brain, much like AstraZeneca's safety issue.
The US Food and Drug Administration said it was studying whether the technology behind both vaccines was connected to the clotting cases. Both use a modified cold virus as a vector to deliver coronavirus proteins into cells and prompt an immune response.
Together, the two vaccines are supposed to account for more than 25 per cent of global supply in 2021, according to a Reuters tally of public statements and media reports.
The vaccines from Pfizer with German partner BioNTech and Moderna use a different method to protect against Covid-19 that relies on messenger RNA (mRNA) to programme cells to generate immunity to the coronavirus.
Those two shots are already viewed as a preferred choice among wealthy countries, analysts said, based on clinical trial data showing they were more than 90 per cent effective at preventing symptomatic Covid-19. About 120 million Americans have received a Pfizer or Moderna shot so far with no major safety issue identified.
Now, the US and European Union are pushing to stock up on even more of the mRNA vaccines. Japan is also working to secure 100 million doses of Pfizer's shot by the end of June.
"Right now, (mRNA-based shots) are the Lamborghinis or McLarens of Covid-19 vaccines," said Dr Peter Hotez, a vaccine researcher at Baylor College of Medicine in Houston, referring to ultra-high-end luxury automobiles.
J&J and AstraZeneca did not immediately respond to requests for comment.
Both Moderna and Pfizer said they are working to increase output above their 2021 production targets of up to 1 billion and 2.5 billion shots, respectively.
Pfizer this week said it is targeting a 10 per cent increase in US dose deliveries through May and 50 million more doses for Europe in the second quarter of 2021. The EU is also negotiating for up to 1.8 billion Pfizer doses for 2022 and 2023.
German biotech CureVac, which is testing its own mRNA vaccine, on Thursday said requests for its shot have increased over the past few days following the J&J pause. It expects to file for European authorisation in late May or early June.
The higher cost, production limits and demanding requirements for shipping and storage could limit mRNA-based vaccines' availability in lower-income countries, experts said.
"The raw materials needed for mRNA manufacturing and production are not cheap right now," said Mr Hartaj Singh, a biotechnology analyst at Oppenheimer & Co.
"In the second half of this year, we'll see the conversation change to, 'okay, how can we help the developing world get their hands on mRNA vaccines'," Mr Singh said of countries like the US, which has pledged to do so.
Moderna chief executive Stephane Bancel reiterated this week that his company would be able to significantly increase production in 2022.
Reuters on Wednesday reported that Moderna was talking to a US company with capacity to produce 30 million doses of its shot each month.
But poorer countries will likely still have to rely on the vaccines from J&J, AstraZeneca and others from China and Russia that, unlike the mRNA shots, can be stored in a standard refrigerator, making them a better option for rural and hard-to-reach areas.
That could change, said Dr Amesh Adalja, senior scholar at Johns Hopkins Centre for Health Security.
"Hopefully, there will be innovation around the storage of mRNA vaccines that allows them to be used more widely," he said.