New MERS vaccine protects camels. Can it help humans?

It was in the autumn of 2012 when a Saudi Arabian hospital admitted a male patient with pneumonia. His doctors determined his infection was a coronavirus. These beasties are found around the world in a menagerie of critters, including bats, birds, cats, horses, humans, and even whales. Their targets include the lungs, intestines, liver, brain, and spine. But this particular virus was not yet known to science. Eventually, the coronavirus was linked to two related strains, both found in bats. More than a thousand patients later (including 500 who died from it), researchers discovered that the disease that came to be known as MERS, or Middle East Respiratory Syndrome, didn’t come from a bat – it came from camels. Like other coronaviruses including its cousin SARS, MERS is a zoonotic disease, able to pass effortlessly between humans and other animals. Now, a group of veterinary researchers has announced that they’ve developed a vaccine for the humped ungulates.

In 2014, researchers surmised that the virus had been circulating among dromedary camels in the Middle East for at least 20 years before somehow making the leap to our species. Since then, it’s spread to at least 25 countries, thanks to international travelers bringing it with them from the Middle East.

While some researchers work to develop human vaccines, Erasmus Medical Center researcher Bart L. Haagmans led a team working on a way to limit its spread among camels. If the virus can be successfully reduced in its reservoir, dromedary camels, there are fewer chances for it to make the jump to humans. Their results were published last week in the journal Science.

The group took a pox virus and modified it by adding a key protein that helps the immune system mount a defense against coronaviruses, and administered it to four camels at the Centre for Research into Animal Health in Barcelona, Spain. Each animal got a shot in their necks as well as a nasal spray, and those were followed up by another round of inoculations a month later.

Three weeks later, after exposure to the MERS virus, antibodies began to be detectable in the vaccinated camels’ blood. Because they used a pox virus to deliver the vaccine, the camels also developed antibodies against the camelpox virus.

Those who were not vaccinated developed the telltale symptoms, while those who were did not show the characteristic fevers or runny noses.

There are just two problems.

First, a second Science paper published last week showed that there is more than one MERS coronavirus strain circulating amongst camels, three of which are shared with humans. A vaccine against one strain might not work against the others.

Second, the vaccinated camels still excreted the virus, meaning that it could be transferred to another animal, but indeed at a far lower rate.

Additional work needs to be done to make the vaccine more efficiently administered in real-world conditions. Still, farmers might be inclined to do the work to vaccinate their animals, especially since they can guard against not just MERS but also camelpox. They get two vaccines for the price of one.

The researchers say the vaccine they developed can “also be tested for protection of humans at risk, such as healthcare workers and people with camel contacts.” After all, the two species share quite a bit in common despite vast differences. Science Magazine reports that phase I human trials will begin in Hamburg, Germany, next year. – Jason G. Goldman | 23 December 2015

Sources: Haagmans, B.L., et al. (2015). An orthopoxvirus-based vaccine reduces virus excretion after MERS-CoV infection in dromedary camels. Science. DOI: 10.1126/science.aad1283.

Sabir, J. S., et al. (2015). Co-circulation of three camel coronavirus species and recombination of MERS-CoVs in Saudi Arabia. Science. DOI: 10.1126/science.aac8608.

Header image: Dromedary camels, via University of Veterinary Medicine, Hannover.