Johnson & Johnson's two-dose vaccine regimen against Ebola is safe and produces a strong immune response in people 1 year old and older, according to two studies published this week in The Lancet Infectious Diseases.
The studies detailed the results of phase 2 randomized, controlled trials in Sierra Leone, which is one of the three countries that was hit hard during the massive 2014-16 West African Ebola outbreak.
A potentially easier supply chain
Johnson & Johnson's vaccine regimen consists of a dose of the adenovirus vector-based vaccine Ad26.ZEBOV followed 8 weeks later by a different vector-based vaccine called the MVA-BN-Filo.
Because of these results, Johnson & Johnson received approval and marketing authorization from the European Medicines Agency in July 2020 as well as the World Health Organization's prequalification status in April 2021.
"Although the [existing Merck Ebola vaccine, Ervebo,] requires ultracold chain capacity, despite the two-dose regimen, Ad26.ZEBOV and MVA-BN-Filo vaccines are stable for a long time at refrigerator temperatures (4–8°C), an undeniable advantage for rolling out vaccination in low-income and middle-income countries," write Selidji Todagbe Agnandji, PhD, MD, and Marguerite Massinga Loembe, PhD, in a commentary covering both studies.
"Alongside ring vaccination of index case contacts, front-line workers, and healthcare workers with [Ervebo], the Ad26.ZEBOV and MVA-BN-Filo vaccine regimen is a crucial new tool that would enable rollout of immunisation to at-risk individuals in the general population in mass vaccination campaigns, thus contributing to interruption of virus transmission and limiting the spread of the outbreak."
Immune response 89% and up
The phase 2 trials, called EBOVAC1, took place in the Kambia district in northern Sierra Leone. Both the adult and the child analyses found low frequencies of serious adverse events following vaccination: Less than 1% of adults experienced grade 3 solicited adverse events and 1% of children 13 to 17 years did.
The researchers also noted that strong immune response persisted at least 2 years after vaccination.
The adult portion of the trial took place from September 2015 to July 2018 and looked first at 43 adults in an open-label preliminary stage and then at 400 adults divided 3:1 among the vaccine group or a control group (a meningococcal quadrivalent [four-strain] conjugate vaccine followed by a placebo). Data showed that 98% of the vaccinated adults 18 to 69 years old developed immune responses 21 days after the second vaccination (geometric mean binding antibody concentration 4,784 ELISA units per milliliter [EU/mL] in stage 1 and 3,810 EU/mL in stage 2.
Participants in the first group were also offered a booster shot of the Ad26.ZEBOV vaccine 2 years later, which prompted a strong antibody response within a week.
"These findings support the additional strategy of providing an Ad26.ZEBOV booster to previously immunised individuals at the start of an Ebola virus disease outbreak," said co-first author on the adult paper, Daniela Manno, MD, in a London School of Hygiene & Tropical Medicine (LSHTM) press release.
As for the youth portion of the trial, which took place from Apr 4, 2017, to Jul 5, 2018, the researchers randomized 192 children in each age-group of 1 to 3 years, 4 to 11, and 12 to 17. Children were further split among the intervention or control arms, also at a 3:1 ratio.
Twenty-one days after the second vaccination, 98% of children 12 to 17 years, 99% of children 4 to 11 years, and 89% of children 1 to 3 years showed Ebola virus glycoprotein-specific binding antibody responses (9,929 EU/mL, 10,212 EU/mL, and 22,568 EU/mL, respectively).
To date, more than 250,000 people participating in clinical trials and vaccination initiatives have received at least the first dose of the Johnson & Johnson vaccine regimen, according to the LSHTM press release. Future studies will look at inoculating infants under 1 year old as well as immune responses 5 years after vaccination.