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A New Vaccine Against Smallpox Has Been Approved and Added to the Strategic Stockpile


René F. Najera, DrPH

September 25, 2019

The Food and Drug Administration (FDA) announced on September 24, 2019, , that it had approved a new vaccine against smallpox and monkeypox. The vaccine, whose trade name is Jynneos, is created from the same virus used in the current smallpox vaccine, ACAM2000. That virus is the vaccinia virus, the same virus . The difference here is how the virus triggers immunity compared to the previous vaccine. According to the press release:
“Jynneos does not contain the viruses that cause smallpox or monkeypox. It is made from a vaccinia virus, a virus that is closely related to, but less harmful than, variola or monkeypox viruses and can protect against both of these diseases. Jynneos contains a modified form of the vaccinia virus called Modified Vaccinia Ankara, which does not cause disease in humans and is non-replicating, meaning it cannot reproduce in human cells.”
The ACAM2000 vaccine had replicating virus in it, albeit attenuated, meaning that the virus could cause a more widespread infection if care is not taken to cover the injection site. ACAM2000 produces a scar on the arm where it is given, as shown in the following image from the Centers for Disease Control and Prevention (CDC):
After about three weeks (21 days), the scab dries and falls off. The scabbing is an indicator that the vaccine triggered an immune response and that the immune system is primed and ready to take on the real thing if it is ever encountered in the future.

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Because ACAM2000 could replicate inside human cells, the injection site had to be protected so that the person would no scratch the site and spread the virus to other parts of their body. Even with the vaccine used before ACAM2000, there were instances where people receiving the vaccine would contract more widespread inoculation sites on their body or . Hopefully, because Jynneos doesn't replicate inside human cells, these accidental inoculations will be minimized. What about safety and effectiveness? The press release states:
“The effectiveness of Jynneos for the prevention of smallpox was determined in a clinical study comparing the immune responses in study participants who received either Jynneos or ACAM2000, an FDA-approved vaccine for the prevention of smallpox. The study included approximately 400 healthy adults, 18 through 42 years of age who had never been vaccinated for smallpox, in which half of the study participants received two doses of Jynneos administered 28 days apart, and half received one dose of ACAM2000. The group vaccinated with Jynneos had an immune response that was not inferior to immune responses to ACAM2000. Vaccine effectiveness for the prevention of smallpox was also inferred from supportive animal studies that showed prior vaccination with Jynneos protected non-human primates who were exposed to viruses related to the smallpox virus. The effectiveness of Jynneos for the prevention of monkeypox disease is inferred from the antibody responses in the smallpox clinical study participants and from studies in non-human primates that showed protection of animals vaccinated with Jynneos who were exposed to the monkeypox virus. The safety of Jynneos was assessed in more than 7,800 individuals who received at least one dose of the vaccine. The most commonly reported side effects were pain, redness, swelling, itching, firmness at the injection site, muscle pain, headache and fatigue. No safety concerns that would require a Medication Guide have been identified for Jynneos. Jynneos is administered in two doses given four weeks apart.”
Should there ever be the need to mass vaccinate after an intentional or accidental release of smallpox, there is now a new vaccine that can be used. Like the ACAM2000 vaccine, Jynneos .


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