Vaccines used to prevent monkeypox


Monkeypox virus is a DNA virus belonging to Orthopox sex. This genus includes other viruses such as camelpox, cowpox, raccoonpox, skunkpox, smallpox, and licorice. While monkeypox was initially discovered in 1958 in monkeys, rodents are known to be their natural reservoir, and humans and other primates are often occasional hosts. Human infection was first identified in the Democratic Republic of the Congo in 1970. The two most common and distinct strains of monkeypox include the West African strain, which causes less severe infection, and the Central African or Congo Basin strain, which causes a more severe strain. infection.

Infection in humans can occur through contact with infected animals or humans. Human-to-human transmission can occur through contact with a skin lesion or large respiratory droplets. The incubation period can range from 7 to 21 days, and most cases of symptoms are self-limited. Common symptoms include chills, malaise and fever, followed by a centrifugal rash on the soles of the feet and palms. Over the next 2 to 4 weeks, the rash changes from maculopapular to vesicular to pustular to crusty. Moreover, monkeypox infection is often characterized by lymphadenopathy.

However, the current outbreak of monkeypox suggests that the infection may also be asymptomatic with a small number of unsynchronized skin lesions. Most of them appeared in the rectal mucosa, oral mucosa, and genitals, which are the focal points related to sexual positions. This led to a misdiagnosis of monkeypox, along with delayed treatment. Furthermore, reports from Germany and Italy have raised concerns about whether monkeypox is a sexually transmitted disease. In addition, the increase in the number of monkeypox infections in endemic parts of Africa and non-endemic parts of the world could be due to a combination of multiple factors. These factors include the lack of orthopoxvirus cross-protection as a result of the termination of the smallpox vaccination after its eradication in 1980, rapid global travel, and the impact of genetic alterations.

Published a new review in Lancet Infectious Diseases aim to describe effectiveness Virus-based smallpox vaccines against the current outbreak of monkeypox.

Preventing monkeypox with vaccines: a quick review Image Credit: Dotted Yeti / Shutterstock

Preventing monkeypox with vaccines: a quick review. Image Credit: Dotted Yeti / Shutterstock

effect of vaccination

Previous research has shown that orthopoxviruses can recognize each other and provide protection depending on how closely they are related. There has been speculation that the termination of smallpox vaccination may have led to an increase in monkeypox infection. The cross-immune interaction between the two viruses is due to the high sequence similarity between orthopoxviruses and the broad range of immune responses where antibodies target at least 24 structural and membrane proteins. Previous studies using Dryvax or other first generation smallpox vaccines showed complete protection against monkeypox in cynomolgus macaques, rhesus macaques, and chimpanzees.

Currently, two licensed smallpox vaccines are available in the United States, ACAM2000 and JYNNEOS. ACAM2000 is only known to be licensed against smallpox, while JYNNEOS is licensed against both monkeypox and smallpox. ACAM2000 is a second generation vaccine derived from a single clonal viral isolate obtained from Dryvax. Meanwhile, JYNNEOS is a third generation vaccine derived from a non-replicating modified vaccinia virus of the Ankara strain (MVA) in which 10% of its genome has been deleted. These vaccines can be used either before exposure to infection to prevent disease or after exposure to infection to reduce disease severity. In both cases, second- or third-generation vaccines have been found to produce significant results.

However, many side effects of both first and second generation vaccines have been identified. These include pain and swelling at the injection site, muscle aches, fatigue, lymphadenopathy, nausea, and headache. Serious side effects included post-vaccine encephalopathy, eczema vaccination, progressive vaccination, lactation, and death. Common side effects of JYNNEOS reported are fatigue, nausea, headache, chills, and muscle aches. ACAM2000 and JYNNEOS were both found to possess similar immunogenicity, while adverse events were reported to be lower for the latter. Another third-generation vaccine has been reported, LC16m8 derived from the Lister strain used in first-generation vaccines. It is licensed in Japan. However, it has not been submitted to the FDA for authorization in the United States. The immunogenicity and side effects of LC16m8 were observed to be similar to parental Lister strains.

Non-human primate studies

Non-human primates are better models for human disease. Studies of all three generations of vaccines in non-human primates have shown that first-generation vaccines provide the strongest protection. Most of the animals that received these vaccines showed no signs of clinical disease, rash was noted to be limited, and low-level transient viremia was detected. Protection with second-generation vaccines has been found to be similar to first-generation vaccines.

Although third-generation vaccines have been found to provide strong protection, breakthrough infections have been more common. Furthermore, the rash has been reported to be more distinct compared to first or second generation vaccines. It was also found that the antibody titer is slightly higher in the case of the first or second generation vaccine compared to the third generation vaccines.

human studies

Several previous studies reported that prior smallpox vaccination reduces the rate of monkeypox attack as well as causes milder symptoms in vaccinated people than in unvaccinated people. However, one of the critical factors of the current outbreak involves sexual activity. This could indicate a low threshold for infection through sexual activity or a new transmission route. Unfortunately, none of the previous studies evaluated such scenarios. Therefore, more studies are needed to understand the transmission of monkeypox and the efficacy of vaccines against the current outbreak.

Assumptions and interests

The current outbreak of monkeypox has resulted in more than 61,000 confirmed cases in 104 non-endemic countries. Most of these cases have been reported in adult males with a mean age of 38 years. The epidemiological variability of the current outbreak could be due to human behavior, the ability to leave high-risk areas before symptoms appear and reach international destinations within hours, and a previous lack of smallpox vaccination. A notable feature of the current infection is its rapid transmission, which may be due to a viral mutation. Two current viral strains have been identified in the United States that include several mutations indicating long-term subclinical transmission. In addition, the virus causing the current outbreak has been reported to belong to the West African clade, which was previously observed to cause milder disease with lower fatality rates.

However, the establishment of an animal reservoir outside West or Central Africa by monkeypox virus is currently a major concern. This tank can occur in prairie dogs, rodents, or the exotic small pet trade. This could mean that eradication of the disease will not be possible, and it will continue to put the world’s population at risk.


Monkeypox poses a major threat to humans. Groups most at risk include infants, young children, immunocompromised individuals, and pregnant women. Smallpox and monkeypox vaccines and two antivirals are available in the United States to combat the disease. However, it is crucial to decide when to use it. The risks, benefits, availability and usefulness of vaccines will influence such decisions.

In addition, evolution of the monkeypox genome can increase the risk of transmission, resulting in increased virulence, and decreased antiviral efficacy from existing vaccines and drugs. With ongoing challenges related to COVID-19, fragile economies, climate change, supply chain issues, and threats of war, prepare for such risks. Health care providers, public health officials, and the general public must be educated regarding the risk of emerging diseases. Effective tracking, diagnosis, and treatment of such diseases must be developed to ensure global safety.


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