• The results from this stage will determine whether the vaccines protect against symptomatic Covid-19, and whether they should be cleared for widespread use.
• The trials will check for the safety and effectiveness of the vaccine in persons between the ages of 18 to 85 years and will be conducted not only in the US but also in 120 sites globally.
Two of the most advanced experimental anti-coronavirus vaccines entered phase III, the pivotal phase of their trials, on Monday.
In that phase, the first subjects will receive doses of the vaccines developed by Moderna Inc and Pfizer Inc.
Researchers evaluating the vaccines plan to enrol 30,000 people in separate last-stage trials.
The latest development means that Pfizer will be conducting two stages of clinical trials seamlessly, an approach that intends to shorten the time taken to conduct the tests.
The Lancet said phase III final trials are needed to confirm whether any of the vaccine candidates effectively protects against SARS-CoV-2 infection.
"We need more research before we can confirm the vaccine effectively protects against SARS-CoV-2 infection, and for how long any protection lasts," University of Oxford study lead author Andrew Pollard said.
In stage III, scientists give the vaccine to thousands of people and see how many are infected, compared with volunteers who received a placebo (a substance that has no therapeutic effect usually used as a control in testing new drugs).
After this, regulators in each country review the trial results and decide whether to approve the vaccine or not.
The results from this stage will determine whether the vaccines protect against symptomatic Covid-19 and whether they should be cleared for widespread use.
The trials will check for the safety and effectiveness of the vaccine in persons between the ages of 18 to 85 years and will be conducted not only in the US but also in 120 sites globally.
The duo is targeting 39 states across the US as well as countries like Argentina, Brazil and Germany.
Before this, Pfizer-BioNTech had conducted early stage phase I and II trials in the US and Germany.
If the late stage trials succeed in showing that the candidate is effective in preventing a person from getting Covid-19, Pfizer-BioNTech will be “on track” to approaching the American drug regulator for approvals as early as October.
If approval is given, the firm plans to supply up to 100 million doses by the end of 2020 and around 1.3 billion doses by the end of 2021.
Last week, the Lancet journal reported the vaccine — by University of Oxford and drugmaker Astrazeneca — had proved safe and produced an immune response in early-stage clinical trials in healthy volunteers.
Kenyan scientists said the earliest any of the three vaccines, if successful, would be available to the public is next year.
The three must jump the next phase, stage III, which is the most critical - proving they can protect against coronavirus and how long that immunity lasts.
The second vaccine, according to results in the Lancet journal, is a Chinese candidate developed by CanSino Biologics Inc and a military research unit, which is safe and produces strong immune reactions.
Head of Medical Services at Nairobi's MP Shah Hospital Dr Vishal Patel told the Star in the absence of a vaccine, patients are only getting therapies to treat symptoms.
"We are giving some of the treatment modalities that have been seen effective in other areas where studies are being done in countries which have a significant burden of Covid-19," he told the Star.
"So we're treating our severe cases with a steroid called dexamethasone."
Separately, global public health expert Dr Richard Muia said until a vaccine is available, the best Kenyans could do is prevention.
"Our orientation is preventive health, which is much cheaper. We can't keep on building hospitals," he said.
Edited by Henry Makori