By Raymond Carl Gato

International concerns following the outbreak of monkeypox have pushed the World Health Organization (WHO) into declaring a global health emergency after its rapid spread throughout several countries. The Centers for Disease Control and Prevention (CDC), as of this writing, reports 21,148 cases of monkeypox worldwide, with 20,804 of those cases coming from 71 countries that have never previously reported infections with the virus.

The virus originated in the tropical rainforest areas of western and central Africa. Unusually, Europe is currently the global epicenter of the monkeypox virus despite it being non-endemic to the continent. 80% of the total monkeypox infection cases in 2022 are rooted in Europe.

Are vaccines available?

Only two vaccines have received a license from the United States Food and Drug Administration (US FDA) to prevent the monkeypox virus; these are the JYNNEOS and ACAM2000 vaccines. 


Manufactured by the Danish biotechnology company Bavarian Nordic A/S, JYNNEOS is a non-replicating vaccine from strains of Modified Vaccinia Ankara-Bavarian Nordic (MVA-BN), a weakened orthopoxvirus. The vaccine was made to specifically prevent individuals aged 18 and above from acquiring smallpox and monkeypox viruses.

MVA-BN is marketed in the United States as JYNNEOS; Imvanex and Imvamune in Europe and Canada.

JYNNEOS underwent 22 clinical trials. There were no serious unfavorable events because of the vaccine recorded by the reviewers during the period. Two deaths are reported, but they are not related to the MVA-BN. (One death due to an overdose of Xanax and benzodiazepine, and one death due to suicide.)

Vaccine effectiveness against smallpox and monkeypox was inferred by comparing the immunogenicity of MVA-BN to a licensed smallpox vaccine (ACAM2000) based on the Plaque Reduction Neutralization Test (PRNT) using the Vaccinia Virus, Western Reserve strain (VV-WR) and was supported by efficacy data from animal challenge studies. The submitted data supports the effectiveness of a two-dose regimen of MVA-BN in preventing smallpox and monkeypox (BLA Clinical Review Memorandum, 2019, p. 11).

Imvanex, the same MVA-BN marketed in Europe, received marketing authorization from the European Commission on July 25 following the highest-level alert by the WHO. With this approval, Bavarian Nordic can also be sold in Europe as an anti-monkeypox vaccine, aside from smallpox protection.
People who had allergic reactions to the vaccine and its components (gentamicin, ciprofloxacin, egg protein) are advised to seek medical professionals regarding their safety concerns. (California Department of Public Health, 2022, par. 7)


The second available vaccine, ACAM2000, is developed by the American biotech firm Acambis and manufactured by Sanofi Pasteur for protection against the variola virus-caused disease. ACAM2000 contains live vaccinia, a type of virus similar to smallpox but milder. The shot does not cause smallpox, but temporary inflammation in the skin after inoculation could infect vaccine-naive people near the site with the vaccinia virus.

Dryvax, the older vaccine made by Wyeth Pharmaceuticals for preventing smallpox and licensed by the FDA in 1931, contains an outdated technique of using the vaccinia virus grown on the skin of calves, raising concerns about contamination risks despite its having a high efficacy rate. To produce an improved live vaccinia virus vaccine against smallpox, the US government supported the production of ACAM2000, an imitative product to the Dryvax but is propagated in cell culture.

Pre-clinical tests of ACAM2000 in suckling mice show a 50% mortality rate lower than Dryvax’s. 780 vaccine-naive individuals aged 18–30 were inoculated with ACAM2000; 200 subjects were given Dryvax. Study results showed that compared to Dryvax, ACAM2000 had a 100% take-rate, 100% seroconversion, and similar T-cell response. 

In a study of people previously vaccinated against smallpox, 1,242 subjects received ACAM2000 and 405 subjects, including males and females from 31–84 years old, received Dryvax. The percentage of unvaccinated persons who developed a successful immunization reaction was similar to that of Dryvax. ACAM2000 also was found to be acceptable as a booster in those previously vaccinated for smallpox. (U.S. Food and Drug Administration, 2018, para. 8)

People who are pregnant, as well as those who have weak immune systems and skin conditions like atopic dermatitis or eczema, are discouraged from taking ACAM2000.

What are their side effects?

Individuals need to be given two doses of the JYNNEOS vaccine (0.5 mL each) 4 weeks apart to be fully vaccinated against monkeypox. According to the CDC, minor side effects of JYNNEOS include injection site reactions (pain, swelling, firmness, or itching), muscle pain, headaches, nausea, chills, tiredness, and even fever.

Vaccination with ACAM2000, on the other hand, could commonly cause itching, soreness of the arm, fever, headache, body aches, mild rash, and fatigue. Heart inflammation and swelling (myocarditis and pericarditis) could also occur in serious cases. 

Why are smallpox vaccines used as protection against monkeypox?

Monkeypox and smallpox are caused by the same virus, the variola virus. They also originate from the same family of viruses, the poxviridae (poxvirus), which explains why observational studies from Africa show smallpox vaccines provide at least 85% protection against monkeypox.

Amid the limited supply of smallpox vaccines worldwide, the Department of Health (DOH) said they are already working with the WHO to acquire monkeypox shots. Meanwhile, in the United States, there are only 300,000 supplies of two-dose vaccines delivered so far. 

As of now, monkeypox vaccines are only given to individuals who are at high risk of infection from the virus, such as laboratory and healthcare professionals. Dr. Nina Gloriani, an infectious disease expert, said that the current supply of monkeypox vaccines cannot be administered to the general population.