In spite of the number of vaccinated people around the world rising significantly over the past few months, uncertainties about their ability in dealing with COVID-19 reinfections—especially those caused by variations and mutations of the novel coronavirus—persist. But now, researchers appear to have found a stone that kills all birds, in the form of a vaccine that may offer protection from all coronaviruses.

By using an innovative approach, researchers Steven L. Zeichner from UVA Health and Xiang-Jin Meng from Virginia Tech have developed what could one day become a universal vaccine for coronaviruses. This vaccine wouldn’t just fight all the current and future strains of COVID-19-causing SARS-CoV-2, but also the coronaviruses that previously threatened epidemics or cause cases of the common cold on a regular basis.

How can one vaccine fight all coronaviruses?
The vaccine created by Zeichner and Meng takes an unusual approach, in that it targets a part of the virus’ spike protein called the "viral fusion peptide". This fusion peptide is essentially universal among coronaviruses; in fact, it has not changed or differed at all in any of the genetic sequences of SARS-CoV-2 that have been obtained from thousands of patients around the world. The vaccine’s ability to target this universal part is what’s supposed to render it effective against all coronaviruses.

To test its effectiveness, Meng and Zeichner made two vaccines—one designed to protect against COVID-19 in humans, and another to protect against Porcine Epidemic Diarrhea Vaccine (PEDV) in pigs. Both these diseases are caused by distantly related coronaviruses, which share several of the amino acids that constitute the fusion peptide.

Both these vaccines were administered to different groups of pigs, and subsequent analysis revealed that the vaccine for PEDV as well as the vaccine for SARS-CoV-2 protected the pigs against the illness caused by PEDV. While the vaccines did not prevent infection completely, they successfully protected the pigs from developing severe symptoms. Moreover, they also primed the pigs’ immune systems to mount a much more vigorous immune response to the infection.

Through these observations, scientists inferred that if both PEDV and COVID-19 vaccines protected the pigs against disease caused by PEDV and primed the immune system to fight the disease, then it is reasonable to think that the COVID-19 vaccine would also protect human beings against severe coronavirus infections.

Further advantages and future steps
Meng and Zeichner chose to study PEDV in pigs because it offered them the advantage of analysing a vaccine’s performance against a coronavirus infection in its native host—in this case, pigs. The other models that have been used to test COVID-19 vaccines study SARS-CoV-2 in non-native hosts such as monkeys or hamsters. The fact that pigs are very similar in physiology and immunology to humans added to the advantage.

Even though the early evidence demonstrates the effectiveness of the vaccine against all coronaviruses, the researchers insist that additional testing and human trials would be required before the vaccine is approved for mass production and usage.

Overall, the vaccine-development platform designed by Zeichner seems to have ticked all the right boxes, as the vaccine offers a new route to rapidly produce vaccines in existing facilities around the world, and that too at a very low cost. The vaccine can be mass-produced easily and cheaply, as it is created using an existent, widely-used technique that involves the genetic modification of the common bacteria E. coli. Vaccines created using this method are referred to as killed whole-cell vaccines.

“Killed whole-cell vaccines are currently in widespread use to protect against deadly diseases like cholera and pertussis,” Zeichner explained. “Factories in many low-to-middle-income countries around the world are making hundreds of millions of doses of those vaccines per year now, for a $1 per dose or less. It may be possible to adapt those factories to make this new vaccine. Since the technology is very similar, the cost should be similar too.”

Furthermore, the entire process used to create whole-cell vaccines—from identifying a potential vaccine target, to producing the gene-deleted bacteria that have the vaccine antigens on their surfaces—can take place in just two to three weeks, thereby making them ideal for responding to a pandemic.