How are mosquitoes being used to transmit vaccines?


Mosquitoes are, by far, the deadliest animal on the planet. Along with their trademark disease, malaria, they can carry a grab-bag of other deadly pathogens, including West Nile Virus, Japanese Encephalitis, Chagas Disease and Zika Virus. Malaria alone is estimated to cause about 627,000 deaths a year – most of these in poorer, developing nations.

But what if there was a way to use science and tech to turn mosquitoes into something else? A billion, billion tiny, blood-sucking vaccine syringes? In the world of cutting-edge disease prevention, there are scientists working on just that: vaccination via mosquito bite.

What are mosquito borne diseases?

Mosquito bites, by themselves, are relatively harmless. The problem lies in their saliva. When a mosquito bites, its saliva messes up your body’s initial immune response, helping any pathogens slip through your defenses. That’s what makes them so deadly.

Mosquito borne diseases are a nightmare for virologists and doctors, largely because of vectors: billions and billions of disease-carrying delivery drones, each capable of holding multiple pathogens, resistant to insecticide, distributed all over the globe.

In 2020, according to the World Health Organisation, there were approximately 241 million cases of malaria worldwide. 100% of these were transmitted by female Anopheles mosquitoes.

How does mosquito vaccine development work?

There are a few vaccine development labs around the world experimenting with the idea of a mosquito borne vaccine. The basic concept is to use mosquitoes to deliver malaria-causing Plasmodium parasites – genetically modified to not get people sick – into the bloodstream. The body will then make antibodies against these weakened parasites, so it’s better prepared against the real thing.

One study in the University of Washington began human trials in August 2022, with an initial success rate of about 50%. Half the subjects still developed malaria, and for the other half, protection didn’t last longer than a few months. Still, it’s progress.

Potential implications for disease prevention

It’s important to emphasize that the goal here isn’t to unleash zillions of ‘mosquito vaccines’ into the wild. At least, not yet. The University of Washington study was simply using mosquitoes as a more effective delivery system, in the hope that they could develop a better malaria vaccine for disease prevention.

The world’s first malaria vaccine, RTS,S from GlaxoSmithKline, has been approved by the WHO, and while it’s a big deal, its efficacy rate is still only 30-40%. It’s hoped that mosquito transmission will be more effective, because – unlike RTS,S – this method doesn’t just target one potential protein. It uses the whole weakened parasite.

A universal mosquito vaccine

Other labs are taking a slightly different tack. Not vaccination with mosquitoes, but vaccination from mosquitoes. Studies have shown that animals with antibodies to mosquito saliva also have some protection against mosquito borne diseases. So, the theory goes, if we can protect people against mosquito saliva, maybe we can head malaria, dengue fever and West Nile Virus off at the pass.

A research team at America’s National Institute of Allergy and Infectious Diseases (NIAID) is trying exactly that, and the initial results are promising. By administering a vaccine with four synthetic peptides (commonly found in the salivary glands of different mosquito species) the researchers were able to create specific antibodies in the test subjects. This isn’t a mosquito silver bullet – yet – but the potential is enormous.

“A widely available ‘universal’ vaccine could possibly provide protection against emerging and re-emerging mosquito-borne diseases as they arise, allowing public health officials to quickly respond to new outbreaks and epidemics without waiting for new treatments or vaccines to be developed,” research lead Dr. Jessica Manning said.

Will we eventually see vaccine mosquitoes buzzing through the night sky? It’s unlikely at this point. There are simply too many variables – how many times would each mosquito bite a host? How much vaccine would each person receive? And how would people give consent? No regulatory agency would sign off on releasing a drug like that into the wild, and who would pay for the whole thing?

Still, mosquito-vaccine-delivery could be an effective way to design and test vaccines in the lab. Who knows? The saliva of nature’s greatest killer could also be our greatest salvation.