A vaccine designed to produce immunity against the most stable portion of coronaviruses has been found to neutralize viruses in mice. If the work can be translated to humans – something the researchers acknowledge is a fair way off – it could give us insurance against the next member of the viral family to jump from animals to humans, even if it is considerably worse than COVID-19.
After the original SARS outbreak in the early 2000s, virologists realized it was only a matter of time before we encountered something much harder to fight. Since we couldn’t know the details of what we would be facing, the only option was to find a way to vaccinate against a common feature of all coronaviruses, similar to the quest for a universal flu vaccine.
Although several teams made progress in this direction, funding bodies didn't grasp the urgency and work moved slowly or petered out for lack of support. Now things look different, a team at Osaka University has now announced a major step forward in the Journal of Experimental Medicine.
“Given that prior coronavirus epidemics such as SARS-CoV-1 and MERS-CoV have occurred due to zoonotic coronaviruses crossing the species barrier, the potential for the emergence of similar viruses in the future poses a significant threat to global public health, even in the face of effective vaccines for current viruses.” Professor Tomohiro Kurosaki said in a statement.
COVID-19 vaccines famously target the crucial “spike” protein the virus uses to enter human cells. However, the spike actually consists of two parts: a “core” and “head”. The core is largely unchanged in all the coronaviruses that have been investigated, whereas the head of the spike differs in SARS-CoV-2 compared to other coronaviruses. Worse still, the head has changed enough between different COVID-19 variants to undermine the effectiveness of vaccines designed against the original strain against new variants, although so far not as much as anti-vaxxers like to claim.
A vaccine that produces antibodies against the core could protect against all strains of COVID-19, the original SARS if it came back, and the periodically returning MERS. Hopefully, it would also work against whatever comes next.
This is no easy task, however. The immune system is so busy responding to the spike's head, few antibodies against the core are produced by existing vaccines. Kurosaki sought to get around this by producing SARS-CoV-2 proteins whose heads are covered with sugar molecules, reducing the threat the immune system experiences.
When Kurosaki immunized mice with these sugar-coated spike vaccines they produced far more core-targeting antibodies. When the same mice were exposed to SARS-CoV-2, these antibodies still did a good job of stopping the virus entering their cells.
More significantly, however, these mice also had gained partial immunity against SARS-CoV-1 and three coronaviruses that infect bats and pangolins but haven't affected humans (yet).
“Our data suggest that engineered versions of the spike receptor-binding domain could be a useful component for the development of broadly protective, next-generation vaccines to prevent future coronavirus pandemics,” Kurosaki said.
Other teams are also chasing the dream of broad-spectrum coronavirus vaccines, with clinical trials underway for one that may protect against at least those most closely related to each other.