Woman Bitten by More Than 600 Mosquitoes in Malaria Vaccine Trial



  • Malaria kills hundreds of thousands of people every year.
  • One Seattle woman recently tried out a new malaria vaccine — administered through biting mosquitoes.
  • The vaccine was about 50% effective. The participant got malaria, but was treated quickly.

When Carolina Reid arrived for her vaccine, the mosquitoes were hungry. Roughly 200 females had been starved overnight, just waiting for her. 

Inside a lab where others were enveloped in full-body suits, hooded and zipped so no skin was exposed, the only special equipment Reid deployed against the insects was her own body odor. No showering beforehand, researchers had told her, to better attract the bugs.

She quietly lowered her smelly arm over a takeout container where a troupe of roughly 200 female mosquitoes was silently flying around. Knowing the insects would prefer to feast in darkness, Reid covered the whole contraption with a towel, and waited for them to land. 

“It was not fun,” Reid, a 30-year-old chef from Seattle, told Insider. 

She sat in silence, waiting for the 10-minute bloodbath to be over, as her forearm got covered in bites. “I would’ve screamed if I said anything out loud,” she said.

These mosquitoes had an important job to do: they injected Reid with a special modified malaria parasite — one safely designed to stop growing once it got inside her liver, which is where malaria parasites mature in people before they re-enter the bloodstream and cause disease. 

The mosquitoes were her vaccinators, injecting a new type of anti-malaria vaccine in her, in a small clinical trial run by malaria expert Dr. Sean Murphy from the University of Washington. 

Mosquitoes can do their own vaccine manufacturing

woman wearing mask, dissecting mosquitos under microscope

Researchers at the Naval Medical Research Center also have a long history of using mosquitoes in vaccine trials.

US Navy photo by Michael Wilson.



The reason malaria researchers use mosquitoes as vaccinators is because it allows them to quickly test out new vaccine candidates, without having to go through the entire process of manufacturing a shot. Instead, the mosquitoes do the work of growing the modified sporozoite, meant to train the body to fight off malaria.

If a successful vaccine is subsequently developed, it will be manufactured as a regular shot, with needles.

“Mosquitoes are highly efficient delivery bots to introduce these attenuated versions of the parasite that may prove to be highly effective in preventing malaria,” Dr. James Kublin, who directs the Seattle Malaria Clinical Trials Center, said. 

The US Navy has been doing this kind of vaccination-by-mosquito-bite for decades, hoping that one day, a successful vaccine may be used by its sailors.

man in navy uniform, holding malaria mosquitos in container

Navy Captain Dr. Stephen Hoffman of the Naval Medical Research Center holds a container of mouse malaria-carrying mosquitoes, circa 1997.

US Navy



A ‘morning coffee shop’ where you get blood drawn

Reid was vaccinated by mosquitos not one, not two, but five times over a period of several months — for a grand total of more than 600 bites. Each visit, she’d get bitten by a few hundred mosquitos, receive a few hundred dollars, then go in for blood draws regularly in the days afterwards. Hot, red, burning reactions were the norm for a few days afterwards. 

“It just became this place that I knew the people,” she said of the lab. “It’s like your morning coffee shop.”

three side by side photos of carolina's arm, covered in bites

What Carolina’s arm looked like just after her mosquito-bite vaccines.

Carolina Reid



Finally, after several months of bites and blood tests, Reid was bitten one last time — this time by five real, infection-producing malaria mosquitos, in what’s called a vaccine “challenge.”  

Challenge trials are critical for malaria vaccine research, because they give researchers a controlled environment to figure out how well different people’s immune systems are responding to their jabs (or, bites in this case.) 

Reid was feeling confident about her malaria protection. It had been several months already since her vaccinations, plenty of time for her immune system to develop a good response.

two women in masks, holding cage of mosquitos

Vaccine researchers in Sean Murphy’s lab at the University of Washington. Murphy’s malaria trial was the product of a multi-institution effort between Kaiser Permanente Washington Health Research Institute, Seattle Children’s Research Institute, the University of Washington, and the Fred Hutchinson Cancer Research Center.

Murphy lab, University of Washington



So it came as quite a surprise when, several days after her malaria mosquito challenge, her blood tested positive for the parasite plasmodium falciparum

Reid had malaria.

She burst into tears. This wasn’t how a successful vaccine trial was supposed to end, she thought.

“All of this research, all of this work that all of these other people did, they didn’t get the outcome that they wanted,” she said. 

People often don’t realize they’re infected with malaria until it’s too late

Malaria is a tricky disease to prepare a vaccine against. It’s a stealth pathogen — once it enters the body, it makes a beeline for the liver, spending at least six days there before people get symptoms. There are some highly effective, well-established malaria drugs available, but the disease remains deadly, because treatment needs to start early, and many people don’t realize they have it until it’s too late. 

In 2018, for example, a 24-year-old Peace Corps volunteer serving in The Comoros died of malaria, after she complained of dizziness, nausea, headaches, dehydration, fatigue, and chills for about a week. A 23-year-old navy sailor deployed to Liberia was killed by the same parasite in 2009.

Their deaths represent just two of the more than half a million malaria fatalities happening around the world every year, many in newborns. (The US got rid of malaria in the late 1940s by spraying the toxic bug-killer DDT around hotspots.)

The current malaria vaccine only offers 30% protection

woman holding baby with worried look

Reshma with her son, Shriaz Ali, who was running a high fever due to malaria, on September 14, 2022. This malaria outbreak was spurred by flooding in Pakistan.

Saiyna Bashir/The Washington Post via Getty Images



The first malaria vaccine, Mosquirix (or RTS/S), was recommended by the WHO last year, but it’s only about 30% effective, and that’s with four doses, providing protection for maybe about four years. Disease experts would like to find a vaccine that can maintain at least 75% effectiveness. 

A new malaria vaccine candidate just tested by the University of Oxford may work better than Mosquirix, with researchers touting around 77% efficacy, but the reality is we only know that vaccine performed well for one malaria season (about 6 months) and it also requires at least four shots. That’s no easy feat when you’re working with children and families living in remote areas, often far from any health services.

Kubin, the vaccine researcher, said being in a trial like the one Reid participated in “requires battling every atavistic impulse” in our bodies, but he’s tried mosquito bite vaccines too. He said if it “accelerates the safe, ethical evaluation of the malaria candidate vaccine, I’m all for it.”

Reid’s malaria treatment was ‘boring’ and she got a $4,200 paycheck

After her malaria diagnosis, Reid was swiftly prescribed Malarone, and while the drug wiped her out for a couple of days, she never experienced any malaria symptoms. Treatment was swift, “boring,” and effective, she said.

woman smiling, getting blood drawn in malaria vaccine trial

Reid, getting blood drawn at one of her many clinic visits.

Carolina Reid



But the diagnosis also meant she had to quit the study early with around $4,200 in hand, instead of the $5,500 she initially thought she might make during the trial. 

Now that it’s all over, people often applaud Reid when she tells them about her challenge. 

“Most people are like, ‘Wow, how brave of you!’” she said. 

She finds it “weird” and doesn’t think her participation is anything in need of praise. She knows clinical trials follow rigorous safety protocols, plus she’s making money doing it, “so don’t worry,” she said. 

Researchers will use the information gleaned from her malaria infection to determine their next steps in vaccine development. Since this vaccine was about 50% effective, they can use information about both the successful and the unsuccessful immune responses like Reid’s to work on a better formulation.

If they find it, the anopheles mosquito may one day truly be just a nuisance, instead of a tiny, flying assassin.



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