The vaccine, which was tested on mice by researchers at the University of Pittsburgh School of Medicine, generated the antibodies in quantities thought to be enough to “neutralise” the virus within two weeks of injection.
The study’s authors are now set to apply to the US Food and Drug Administration for investigational new drug approval ahead of phase one human clinical trials planned to start in the next few months.
Scientists across the globe are racing to develop a vaccine to protect against coronavirus, which has infected more than a million people worldwide and claimed 50,000 lives.
The first human trial of a vaccine began at a lab in Seattle last month after a team of US researchers skipped animal testing, which is used to establish effectiveness and safety.
Dozens of other teams around the world have potential vaccines in development.
But the Pittsburgh research is the first study on a Covid-19 vaccine candidate to be published after review from fellow scientists at outside institutions.
The scientists were able to act quickly because they had already laid the groundwork during earlier epidemics of coronaviruses: Sars in 2003 and Mers in 2014.
“These two viruses, which are closely related to [Covid-19], teach us that a particular protein, called a spike protein, is important for inducing immunity against the virus. We knew exactly where to fight this new virus,” said Andrea Gambotto, associate professor of surgery at the Pittsburgh School of Medicine.
The vaccine candidate, which the authors are calling PittCoVacc, uses lab-made pieces of viral protein to build immunity in the same way as a flu jab.
To increase potency, the researchers also used a new drug delivery approach involving of a fingertip-sized patch of 400 tiny microneedles that inject the spike protein pieces into the skin, where the immune reaction is strongest. The patch is stuck on like a plaster and the needles – which are made entirely of sugar and the protein pieces – simply dissolve into the skin.
“We developed this to build on the original scratch method used to deliver the smallpox vaccine to the skin, but as a high-tech version that is more efficient and reproducible patient to patient,” said study co-author Louis Falo, professor and chair of dermatology. “And it’s actually pretty painless – it feels kind of like Velcro.”
The researchers said their system could be scaled up to produce the protein on an industrial scale. Hundreds of millions of doses will need to be produced worldwide.
Once manufactured, PittCoVacc can sit at room temperature until it is needed, eliminating the need for refrigeration during transport or storage, the researchers said.
“For most vaccines, you don’t need to address scalability to begin with,” Prof Gambotto said. “But when you try to develop a vaccine quickly against a pandemic that’s the first requirement.”
When tested in mice, PittCoVacc generated a surge of antibodies against Covid-19 within two weeks of the microneedle prick.
The results have not yet been tracked in the long term, but the mice who were given the Pittsburgh researchers’ Mers vaccine candidate developed enough antibodies to neutralise the virus for at least a year. The antibody levels of the rodents vaccinated against Covid-19 “seem to be following the same trend,” according to the researchers.
The team found the Covid-19 microneedle vaccine maintained its potency even after being sterilised with gamma radiation, an important step in making the drug suitable for use in humans.
Testing in patients would “typically require at least a year and probably longer”, Prof Falo said.
But he added: “This particular situation is different from anything we’ve ever seen, so we don’t know how long the clinical development process will take. Recently announced revisions to the normal processes suggest we may be able to advance this faster.”
Scientists in Australia announced on Thursday they had begun testing another potential Covid-19 vaccine on ferrets, with a team at the University of Oxford set to trial the same drug on humans in the next few weeks.