Mpox Vaccine Reduces Infection Risk by 86%; First Peer-Reviewed Study of Real World Results
HPV vaccine
World’s first peer-reviewed study gives a shot in the arm to Bavarian Nordic’s Mpox vaccine.

Just one shot of the Mpox vaccine reduces the risk of infection by 86% compared to those who are unvaccinated, according to a new study published recently in Nature Medicine.

The real-world study – the first to be published in a peer-reviewed journal since the outbreak began last spring  – tested the effectiveness of a single dose of the live attenuated vaccine, produced by Bavarian Nordic (MVA-BN) in preventing cases of symptomatic infection. 

It comes as WHO’s Mpox Emergency Committee reconvenes again on Thursday to reconsider whether the global public health emergency declared last July may be over, in light of the sharp decline in cases recently – thanks in part to the worldwide response focusing on the vaccination of high-risk groups and other public health measures.

The observational study, conducted by Israel’s largest health fund, Clalit Health Services, followed 2,054 men, who were eligible for the vaccine, 50% of whom were vaccinated during the study recruitment period and completed at least 90 days of follow-up. During the study period, only 5 members of the vaccinated group came down with symptomatic Mpox infection, as compared to 16 cases in the unvaccinated individuals, respectively. 

The health fund conducted a major outreach drive to health fund members determined to be at high risk for contracting the virus, and therefore eligible to receive a vaccine, after Mpox vaccines became available last July.

The study’s analysis also considered risk factors such as age, socioeconomic status and comorbidities. The average age of the patients was 34. The heath fund and national health authorities also ran an awareness campaign focusing on careful sexual behavior among the LGBT population during the study period. It is possible that the information campaign also affected risk-taking behaviour of individuals, and thus study results, the researchers noted. 

Only a handful of other studies have yet produced findings on the vaccine’s real-world efficacy, but they have not yet been published in peer reviewed journals. One retrospective analysis by the US CDC published in October 2022, found unvaccinated men had a 14 times higher risk of becoming infected as vaccinated men, aged 18-48. Smaller studies or less well- controlled studies have reported similar findings in pre-print articles and journal  communications.  

Single dose regime used – with subcutaneous administration

The study is also striking because in light of the global vaccine shortage, it relied upon a single dose of the vaccine – despite the fact that the US CDC recommendation, where the vaccine first received regulatory approval, is for a two dose-regime – administered four weeks apart.  

However in Israel, as elsewhere, public health authorities resorted to single jabs to stretch scarce Mpox vaccine supplies.  The vaccine, however, was administered in the traditional manner with an injection to the subcutaneous layer of skin tissue, which lies just above the muscle.  That as compared to the shallower, intradermal administration of a smaller vaccine dose – which the US Health and Human Services, had authorized in August 2022 – but which many health experts said could be a gamble.   

When vaccination began in Israel, at the end of July, the jab was initially offered only to people deemed to be at maximum risk of contracting and spreading the disease. The criteria for eligibility for vaccination were defined by the Ministry of Health in cooperation with Clalit and based on the findings of a preliminary study by the team of researchers who identified the main risk factors for Mpox morbidity prior to the start of the vaccination campaign.  They then used advanced digital technology to match those criteria with the records of patients deemed to be at high risk. 

WHO Emergencies Committee to meet soon to reconsider Mpox public health emergency

Source: WHO

WHO declared Mpox to be a public health emergency of international concern (PHEIC) on 23 July 2022, after more than 16,000 cases were reported in 75 countries within a matter of weeks. The organization subsequently called for a worldwide vaccination campaign for high-risk populations. 

However, with Mpox cases now in a sharp decline, WHO’s Mpox Emergency Committee is due to meet soon to reconsider the status of the public health emergency, Dr Tedros Adhanom Ghebreyesus said during last week’s WHO Executive Board meeting.

The latest global trends show new case reports declining to just 159 in the week of 30-January to 6 February, roughly compared to the levels reported when the first widespread wave of cases outside Africa began, in May 2022.  This is as compared to about 7,000 new cases a week at the height of the outbreak.

Mpox belongs to the family of viruses that previously caused smallpox, although it is less virulent. People tend to catch the virus from person-to-person contact, mainly via sexual intercourse. Of course, it can also spread from direct contact with the rash or the bodily fluids of an infected person. 

Ultimately, more than 85,000 people worldwide have been verified as infected with the virus as of January 25, 2023. Around 85 people have died so far. 

Image Credits: US National Cancer Institute, Unsplash, National Cancer Institute on Unsplash.

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