LONDON - ENGLAND - SEPTEMBER 17: Dr Felicity Hartnell, who is a clinical research fellow at Oxford University, holds the vile of the ebola vaccine called Chimp Adenovirus type 3 (ChAd3) before the first healthy UK volunteer receives an ebola vaccine at the Oxford Vaccine Group Centre for Clinical Vaccinology and Tropical Medicine (CCVTM) on September 17, 2014 in Oxford, England. (Photo by Steve Parsons-WPA Pool/Getty Images)
PHOTO: WPA Pool/Getty Images Europe/Getty Images
LONDON - ENGLAND - SEPTEMBER 17: Dr Felicity Hartnell, who is a clinical research fellow at Oxford University, holds the vile of the ebola vaccine called Chimp Adenovirus type 3 (ChAd3) before the first healthy UK volunteer receives an ebola vaccine at the Oxford Vaccine Group Centre for Clinical Vaccinology and Tropical Medicine (CCVTM) on September 17, 2014 in Oxford, England. (Photo by Steve Parsons-WPA Pool/Getty Images)
Now playing
01:32
The death of Ebola?
PHOTO: Alberto Mier/CNN
Now playing
02:18
This is the messy truth about Ebola
Health care workers, wearing protective suits, leave a high-risk area at the French NGO Medecins Sans Frontieres (Doctors without borders) Elwa hospital on August 30, 2014 in Monrovia. Liberia has been hardest-hit by the Ebola virus raging through west Africa, with 624 deaths and 1,082 cases since the start of the year. AFP PHOTO / DOMINIQUE FAGET        (Photo credit should read DOMINIQUE FAGET/AFP/Getty Images)
PHOTO: DOMINIQUE FAGET/AFP/Getty Images
Health care workers, wearing protective suits, leave a high-risk area at the French NGO Medecins Sans Frontieres (Doctors without borders) Elwa hospital on August 30, 2014 in Monrovia. Liberia has been hardest-hit by the Ebola virus raging through west Africa, with 624 deaths and 1,082 cases since the start of the year. AFP PHOTO / DOMINIQUE FAGET (Photo credit should read DOMINIQUE FAGET/AFP/Getty Images)
Now playing
02:29
Questions and answers about Ebola
eitm gupta ebola symptoms origins_00011224.jpg
PHOTO: CDC
eitm gupta ebola symptoms origins_00011224.jpg
Now playing
03:44
The facts about Ebola
Now playing
02:03
Virus hunter: The woman who chases Ebola
uk ebola discovery spread soares pkg_00004912.jpg
PHOTO: Courtesy CDC
uk ebola discovery spread soares pkg_00004912.jpg
Now playing
02:28
The origin of the Ebola virus
When the Ebola virus was found in Dr. Ian Crozier's eye, the eye started losing its original blue hue, he told the New York Times.
PHOTO: Emory Eye Center
When the Ebola virus was found in Dr. Ian Crozier's eye, the eye started losing its original blue hue, he told the New York Times.
Now playing
01:02
Ebola found in doctor's eye
rewind ebola victims Nancy Writebol orig_00000619.jpg
rewind ebola victims Nancy Writebol orig_00000619.jpg
Now playing
02:20
Nancy Writebol: 'I was in pretty bad shape'
A health worker, wearing Personal Protective Equipment (PPE), and a woman pose on September 7, 2014 inside the high-risk area at Elwa hospital in Monrovia, which is run by the non-governmental  international organization Medecins Sans Frontieres (Doctors without Borders -- MSF). US President Barack Obama said in an interview aired on September 7 the US military would help in the fight against fast-spreading Ebola in Africa, but warned it would be months before the epidemic slowed. The tropical virus, transmitted through contact with infected bodily fluids, has killed 2,100 people in four countries since the start of the year -- more than half of them in Liberia.   AFP PHOTO / DOMINIQUE FAGET        (Photo credit should read DOMINIQUE FAGET/AFP/Getty Images)
PHOTO: DOMINIQUE FAGET/AFP/AFP/Getty Images
A health worker, wearing Personal Protective Equipment (PPE), and a woman pose on September 7, 2014 inside the high-risk area at Elwa hospital in Monrovia, which is run by the non-governmental international organization Medecins Sans Frontieres (Doctors without Borders -- MSF). US President Barack Obama said in an interview aired on September 7 the US military would help in the fight against fast-spreading Ebola in Africa, but warned it would be months before the epidemic slowed. The tropical virus, transmitted through contact with infected bodily fluids, has killed 2,100 people in four countries since the start of the year -- more than half of them in Liberia. AFP PHOTO / DOMINIQUE FAGET (Photo credit should read DOMINIQUE FAGET/AFP/Getty Images)
Now playing
00:56
In first, 3 'Ebola countries' had no new cases in 1 week
teenages creats ebola test vause intv_00013606.jpg
PHOTO: Google
teenages creats ebola test vause intv_00013606.jpg
Now playing
02:29
Teenager creates Ebola diagnostic test
ebola vaccine edmunds mann wrn_00005109.jpg
PHOTO: Getty Images
ebola vaccine edmunds mann wrn_00005109.jpg
Now playing
03:12
WHO: Trials show Ebola vaccine is 'highly effective'
PHOTO: ZOOM DOSSO/AFP/Getty Images
Now playing
01:10
Liberia celebrates beating Ebola with farewell party
pkg amanpour ebola update_00012719.jpg
PHOTO: Getty Images
pkg amanpour ebola update_00012719.jpg
Now playing
01:55
Positive signs in Ebola fight, but still no victory
pkg magnay ebola sierra leone care centers_00014408.jpg
pkg magnay ebola sierra leone care centers_00014408.jpg
Now playing
03:41
Sierra Leone FM: Ebola spread must reach zero
pkg magnay guinea ebola patient zero_00012311.jpg
pkg magnay guinea ebola patient zero_00012311.jpg
Now playing
03:04
Ebola 'patient zero's' dad: I thought it was witchcraft

Story highlights

A new study found an Ebola vaccine protected 100% of people who received it

The strategy used to deliver it was inspired by the strategy to eliminate smallpox

(CNN) —  

An experimental vaccine against the Ebola virus was found to be 100% effective, according to a study published in The Lancet on Thursday.

The results offer hope of better protection against the disease that ravaged West Africa in 2014, killing more than 11,000 people.

“Ebola left a devastating legacy in our country. We are proud that we have been able to contribute to developing a vaccine that will prevent other nations from enduring what we endured,” said Dr. KeÏta Sakoba, the director of the national agency for health security in Guinea.

The vaccine

The experimental vaccine was given in 2015 to people in Guinea who were in contact with patients who had recently confirmed cases of Ebola.

A few months after the early trials, the World Health Organization said the preliminary results were an “extremely promising development.”

Initially, only people over the age of 18 were offered the vaccine and the participants receiving them were randomized.

But the process was stopped after initial results in order to get the vaccine to everyone in need of it.

The trial involved more than 11,000 people, according to the WHO who led the trial in conjunction with Guinea’s Ministry of Health.

When analyzing the results, the teams didn’t count people who got sick within the 10 days, as they were believed to have been infected before they received the vaccine. Waiting 10 days also gave volunteers time to build up an immunity after receiving the vaccine, according to Dr. Marie-Paule Kieny, the WHO assistant director-general and the study’s lead author.

Patients were either vaccinated immediately or after three weeks. As everyone had become eligible for the vaccine, the three-week group served as the control as they didn’t actually get the vaccine until it was clear that they were not infected (Ebola has an incubation time of two to 21 days), Kieny said.

Researchers followed up with immunized volunteers at their homes on days three, 14, 21, 42, 63 and 84 after receiving the vaccine.

02:14 - Source: CNN
American couple rally to help Ebola's orphaned children
cnni elbagir interview couple helping ebola orphans_00012006.jpg
cnni elbagir interview couple helping ebola orphans_00012006.jpg
Now playing
02:14
American couple rally to help Ebola's orphaned children
lok robertson uk ebola patient london_00011927.jpg
lok robertson uk ebola patient london_00011927.jpg
Now playing
03:54
Ebola patient moved to London hospital
wrn foster spanish nurse ebola_00021921.jpg
wrn foster spanish nurse ebola_00021921.jpg
Now playing
02:52
Ebola survivor alive but mourns dog
Time Magazine announced Wednesday, Dec. 10, 2014, that the Ebola fighter, doctors and nurses who fight to keep the epidemic in check, were its Person of the Year.
PHOTO: From Time Magazine
Time Magazine announced Wednesday, Dec. 10, 2014, that the Ebola fighter, doctors and nurses who fight to keep the epidemic in check, were its Person of the Year.
Now playing
04:08
Time names 2014 'Person of the Year'
ac dnt gupta ebola unknowns_00005517.jpg
PHOTO: CDC
ac dnt gupta ebola unknowns_00005517.jpg
Now playing
02:53
What we still don't know about Ebola
SGMD Gupta Ebola Suit Demo_00003310.jpg
SGMD Gupta Ebola Suit Demo_00003310.jpg
Now playing
03:08
See the suit designed to protect doctors from Ebola
erin dnt burnett dallas nurse profile _00000205.jpg
PHOTO: Facebook
erin dnt burnett dallas nurse profile _00000205.jpg
Now playing
01:18
Who is nurse Nina Pham?
DALLAS, TX - OCTOBER 12: G.C. Williford, Battalion Chief for the Dallas Fire Department, walks past a barrel containing waste material that was removed from the apartment where a second person has been diagnosed with the Ebola virus on October 12, 2014 in Dallas, Texas. A female nurse working at Texas Heath Presbyterian Hospital, the same facility that treated Thomas Eric Duncan, has tested positive for the virus. (Photo by Mike Stone/Getty Images)
PHOTO: Mike Stone/Getty Images
DALLAS, TX - OCTOBER 12: G.C. Williford, Battalion Chief for the Dallas Fire Department, walks past a barrel containing waste material that was removed from the apartment where a second person has been diagnosed with the Ebola virus on October 12, 2014 in Dallas, Texas. A female nurse working at Texas Heath Presbyterian Hospital, the same facility that treated Thomas Eric Duncan, has tested positive for the virus. (Photo by Mike Stone/Getty Images)
Now playing
03:09
CDC: Protocol 'breach' led to infection
cnn tonight heather ebola _00010314.jpg
cnn tonight heather ebola _00010314.jpg
Now playing
04:02
Neighbor describes nurse with Ebola
newday cohen dallas nurse contracts ebola_00003213.jpg
newday cohen dallas nurse contracts ebola_00003213.jpg
Now playing
01:37
Nurse had extensive contact with Ebola patient
CORRECTS BYLINE - Police stand guard outside the apartment of a hospital worker, Sunday, Oct. 12, 2014, in Dallas. The Texas health care worker, who was in full protective gear when they provided hospital care for Ebola patient Thomas Eric Duncan, who later died, has tested positive for the virus and is in stable condition, health officials said Sunday. (AP Photo/LM Otero)
PHOTO: LM Otero/AP
CORRECTS BYLINE - Police stand guard outside the apartment of a hospital worker, Sunday, Oct. 12, 2014, in Dallas. The Texas health care worker, who was in full protective gear when they provided hospital care for Ebola patient Thomas Eric Duncan, who later died, has tested positive for the virus and is in stable condition, health officials said Sunday. (AP Photo/LM Otero)
Now playing
01:09
Imagine getting this call about Ebola
PHOTO: Alberto Mier/CNN
Now playing
02:18
This is the messy truth about Ebola
ctn pkg feyerick little liberia ebola_00023022.jpg
ctn pkg feyerick little liberia ebola_00023022.jpg
Now playing
02:37
NYC's 'Little Liberia' prepares for Ebola
Medical workers wearing protective clothing arrive at an apartment building, the private residence for Spanish nurse, Teresa Romero who has tested positive for the Ebola virus on October 8, 2014 in Alcorcon, near Madrid, Spain.
PHOTO: Pablo Blazquez Dominguez/Getty Images
Medical workers wearing protective clothing arrive at an apartment building, the private residence for Spanish nurse, Teresa Romero who has tested positive for the Ebola virus on October 8, 2014 in Alcorcon, near Madrid, Spain.
Now playing
02:33
'Big mistake' may spread Ebola in Spain
Thomas Eric Duncan
PHOTO: From Facebook
Thomas Eric Duncan
Now playing
01:10
Thomas Eric Duncan's last words
nr cohen ebola possible texas patient _00001817.jpg
nr cohen ebola possible texas patient _00001817.jpg
Now playing
03:02
New patient in Texas monitored for Ebola
tsr dnt marsh ebola airport screenings_00000719.jpg
PHOTO: CNN
tsr dnt marsh ebola airport screenings_00000719.jpg
Now playing
01:57
Airports prepare for Ebola screenings
ac bts mason texas ebola death thomas eric duncan_00004810.jpg
ac bts mason texas ebola death thomas eric duncan_00004810.jpg
Now playing
02:50
Pastor: Family devastated by Ebola death
MADRID, SPAIN - OCTOBER 08: Policemen pull from an animal rights protester as a van allegedly containing the dog named Excalibur drove away from an apartment building, the private residence for Spanish nurse Teresa Romero who has tested positive for the Ebola virus on October 8, 2014 in Alcorcon, near Madrid, Spain. Teresa's dog is thought to be at risk of being put down as health officials try to keep the virus from spreading. Spanish Health Minister Ana Mato confirmed nurse, Teresa Romero had tested positive after treating two Ebola patients who had been brought back to the country from Africa. (Photo by Pablo Blazquez Dominguez/Getty Images)
PHOTO: Getty Images
MADRID, SPAIN - OCTOBER 08: Policemen pull from an animal rights protester as a van allegedly containing the dog named Excalibur drove away from an apartment building, the private residence for Spanish nurse Teresa Romero who has tested positive for the Ebola virus on October 8, 2014 in Alcorcon, near Madrid, Spain. Teresa's dog is thought to be at risk of being put down as health officials try to keep the virus from spreading. Spanish Health Minister Ana Mato confirmed nurse, Teresa Romero had tested positive after treating two Ebola patients who had been brought back to the country from Africa. (Photo by Pablo Blazquez Dominguez/Getty Images)
Now playing
02:43
Tensions rise in Madrid over Ebola dog
pkg elbagir liberia ebola healthcare worker pov_00010705.jpg
pkg elbagir liberia ebola healthcare worker pov_00010705.jpg
Now playing
02:53
Ebola battle through nurse's eyes
dnt fields who is eric duncan_00000223.jpg
dnt fields who is eric duncan_00000223.jpg
Now playing
01:26
Partner of victim: 'His suffering is over'
cnni elbagir spanish nurse dies from ebola _00011710.jpg
cnni elbagir spanish nurse dies from ebola _00011710.jpg
Now playing
01:52
Nurse in Spain tests positive for Ebola
isha sesay emotional ebola outbreak_00012106.jpg
isha sesay emotional ebola outbreak_00012106.jpg
Now playing
01:40
Ebola: CNN anchor's emotional plea