Effect of prior immunisation with smallpox vaccine for protection against human Mpox: A systematic review

Abstract

Monkeypox is an emerging threat to humans since a new outbreak in May 2022. It is hypothesised that increasing the immunologically naive population after the cessation of the smallpox vaccination campaign in the 1980s is one of the leading causes of it. A literature search was conducted using different electronic databases including MEDLINE (through PubMed), SCOPUS, Web of Science, Cochrane library, and EMBASE for relevant studies. After duplication removal, abstract and title screening, and full-text screening were done, the data were extracted, tabulated, and analysed. The risk of bias was assessed following the Risk of Bias Assessment tool for Non-randomised Studies. We found a total of 1068 relevant articles and finally, we included 6 articles including 2083 participants. The studies suggested that smallpox is 80.7% efficacious to prevent human monkeypox and the immunity provided by prior smallpox vaccination is long-lasting. Moreover, the smallpox vaccination decreases the risk of human monkeypox by 5.2-folds. Two crosssectional studies based on the Democratic Republic of the Congo (DRC) including a total of around 1800 monkeypox cases found that unvaccinated participants had 2.73 and 9.64-fold increased risk of monkeypox compared to the vaccinated participants. Other studies in USA and Spain also demonstrated that unvaccinated people were more prone to develop monkeypox than vaccinated people. Furthermore, monkeypox incidence has increased by 20 folds, 30 years after the cessation of the smallpox vaccination campaign in DRC. Evidence-based preventive and therapeutic agents are still not available for human monkeypox. Further study should be done to explore the role of the smallpox vaccine in preventing human monkeypox.

Evaluation of Cross-Immunity to the Mpox Virus Due to Historic Smallpox Vaccination

“…Whether the levels of Nabs measured can be considered protective upon infection or vaccination is unknown. Nevertheless, previous studies have shown that smallpox vaccination may confer protection against Mpox [23,24]. Of note, the mean titers of IgG and Nabs measured in our cohort of smallpox-vaccinated individuals are much lower when compared to the levels observed in a population of 18 acutely Mpox-infected individuals tested at our institute, where at 3 weeks post-infection, we observed a mean titer of 2826 for anti-MPXV IgG and 107 for specific Nabs [33].…”

“…In the same model, the passive transfer of human vaccinia-neutralizing antibodies protected non-immunized macaques from severe Mpox disease. According to studies conducted in the 1980s in the Democratic Republic of the Congo, the level of cross-protection against MPXV conferred by previous vaccination against smallpox was estimated to reach 85% [23,24]. During the 2022 MPXV outbreak, the rate of cases reporting smallpox vaccination ranged from 2% in a UK cohort of 156 cases [25], to 7% (3 out of 41 cases) in a Portuguese hospital cohort of patients with MPXV infection [26], and to 18% in a Spanish multicenter cohort (32 out of 181) [27].…”

Aggregation‐Induced Emission‐Based Macrophage‐Like Nanoparticles for Targeted Photothermal Therapy and Virus Transmission Blockage in Monkeypox

“…Currently, conventional strategies for interrupting the transmission of monkeypox virus involve patient isolation, disinfection of linens and clothing used by patients, and avoidance of sexual contact or recommendation of condom use, etc., but their effectiveness remains poor. Although smallpox vaccination can reduce the risk of acquiring monkeypox in healthy individuals, [ 17 ] the supplies of smallpox vaccine are extremely limited and have been monopolized by some high‐income countries or regions, making it difficult to achieve widespread immunization of the entire population. Therefore, we decided to develop a distinctive strategy to target and eradicate monkeypox virus in skin and mucosal lesions, thus blocking virus transmission from its source while at the same time realizing precise therapy of monkeypox.…”

Sub‐lineage B.1.6 of hMPXV in a global context: Phylogeny and epidemiology

“…(iii) The low immunization of the population with the smallpox vaccine, since it is known that it can protect 85% of the monkeypox virus. In Peru, the smallpox vaccination program was successfully concluded in 1978 and on May 8, 1980, during the 33rd World Health Assembly, the world smallpox eradication was officially declared, therefore the entire world population is now unprotected against smallpox 50‐53 14,26,32,54,55 …”

“…In Peru, the smallpox vaccination program was successfully concluded in 1978 and on May 8, 1980, during the 33rd World Health Assembly, the world smallpox eradication was officially declared, therefore the entire world population is now unprotected against smallpox. [50][51][52][53] (iv) The lack of advanced antiviral treatment for monkeypox even though several investigations suggest that Tecovirimat, an antiretroviral indicated for smallpox, would be effective against monkeypox infection, (v) misdiagnosis or lack of timely diagnosis of the disease, given that it is not a disease commonly dispersed in the population, it could be confused with other similar diseases such as herpes, (vi) the presence of asymptomatic patients who will not have any manifestation of the virus, (vii) evident social prejudice among the diagnosed patients, the disclosure of their co. 14,26,32,54,…”