Context
World Health Organization (WHO) declaring monkeypox as a Public H
About monkeypoxealth Emergency of International Concern (PHEIC), governments around the world are initiating steps towards developing or even sourcing a vaccine against monkeypox.
- The monkeypox virus belongs to a family of viruses called orthopoxviruses, which is different from that of the coronaviruses.
- According to the WHO, it is a viral zoonosis — a virus transmitted to humans from animals — with symptoms similar, but less severe to smallpox.
- It is also an enveloped double-stranded DNA virus, unlike the RNA virus, that makes it far more stable and less prone to rapid mutations.
- There are two distinct genetic clades of the monkeypox virus: the central African (Congo Basin) clade and the West African clade.
- The Congo Basin clade has historically caused more severe disease and was thought to be more transmissible.
Monkeypox vaccine
- There is yet no dedicated monkeypox vaccine, but vaccinations against smallpox were found to be 85% effective in preventing smallpox, a disease eradicated in 1980.
- In 2019, the United States Food and Drugs Administration (FDA), approved the JYNNEOS vaccine for the prevention of smallpox, monkeypox and other diseases caused by orthopoxviruses, including vaccinia virus, in adults 18 years of age and older and categorised as having a “high risk of infection.”
- These include contacts of those who have been confirmed to have contracted a monkeypox infection, sexual partners (with contact within previous two weeks) of those confirmed with an infection and those whose immune systems are compromised.
How does JYNNEOS work?
- JYNNEOS, developed by Danish biotechnology company Bavarian Nordic, contains a live vaccinia virus that does not replicate efficiently in human cells.
- The vaccinia virus is the smallpox virus but made incapable of replicating within the body.
- It is administered as two injections 28 days apart.
- The immune response takes 14 days after the second dose.
- The evidence for JYNNEOS’ effectiveness against monkeypox rests on 22 clinical trials that tested the vaccine’s safety on 7,859 people, aged 18-80, who were administered at least one dose of the vaccine.
- Like in other vaccines, a percentage of individuals reported pain, fever, rashes, nausea and chills following the doses.
- The vaccine’s effectiveness was inferred only indirectly by comparing the immunogenicity of JYNNEOS to a licensed smallpox vaccine (ACAM2000) based on a laboratory test called the Plaque Reduction Neutralisation Test (PRNT).
- This test evaluates what quantity of the vaccine was needed to kill the virus made to replicate in a petri-dish.
- The structural similarities to the smallpox virus, the effectiveness of the JYNNEOS is estimated based on comparison to another licensed smallpox vaccine called ACAM2000.
- There is no data yet on JYNNEOS’ effectiveness.
- This is because smallpox has been eradicated and the monkeypox outbreak has risen too rapidly for a traditional phase 3 trial to have evaluated the vaccine’s effectiveness.
- However, there is evidence that the precursor for ACAM2000 was effective in eradicating smallpox.
- The US-based Centers for Disease Control and Prevention said public health officials are concerned about the lack of effectiveness data for JYNNEOS.
- “We do not know if JYNNEOS will fully protect against monkeypox virus infection.
