With a little help from eggs
The first wave of authorized Covid-19 vaccines require specialized, costly ingredients to make. Moderna’s RNA-based vaccine, for instance, needs genetic building blocks called nucleotides, as well as a custom-made fatty acid to build a bubble around them. Those ingredients must be assembled into vaccines in purpose-built factories.
The way influenza vaccines are made is a study in contrast. Many countries have huge factories for making cheap flu shots, with influenza viruses injected into chicken eggs. The eggs produce an abundance of new copies of the viruses. Factory workers then extract the viruses, weaken or kill them and then put them into vaccines.
The PATH team wondered if scientists could make a Covid-19 vaccine that could be grown cheaply in chicken eggs. That way, the same factories that make flu shots could make Covid-19 shots as well.
In New York, a team of scientists at the Icahn School of Medicine at Mount Sinai knew how to make just such a vaccine, using a bird virus called Newcastle disease virus that is harmless in humans.
For years, scientists had been experimenting with Newcastle disease virus to create vaccines for a range of diseases. To develop an Ebola vaccine, for example, researchers added an Ebola gene to the Newcastle disease virus’s own set of genes.
The scientists then inserted the engineered virus into chicken eggs. Because it is a bird virus, it multiplied quickly in the eggs. The researchers ended up with Newcastle disease viruses coated with Ebola proteins.
At Mount Sinai, the researchers set out to do the same thing, using coronavirus spike proteins instead of Ebola proteins. When they learned about Dr. McLellan’s new HexaPro version, they added that to the Newcastle disease viruses. The viruses bristled with spike proteins, many of which had the desired prefusion shape. In a nod to both the Newcastle disease virus and the HexaPro spike, they called it NDV-HXP-S.