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Mpox vaccines reduce the risk of hospitalisation

Hester Phillips

25 October 2023

USA study reports no hospitalisations among people who got mpox after being fully vaccinated, including people with HIV

Monkeypox vaccine, medical needle and doctor nurse with medicine bottle, healthcare vial or booster injection
Photos are used for illustrative purposes. They do not imply health status or behaviour. Credit: iStock/Jacob Wackerhausen

People who get mpox after having at least one dose of mpox vaccine are less likely to need hospital care than people who are unvaccinated, data from California suggests. And this includes people with HIV.

What is the research about?

The research looked at how severe mpox is in people who get it after being vaccinated.

The study from the US Centers for Disease Control and Prevention is based on data from the California Department of Public Health. It assessed the effectiveness of the Jynneos vaccine, which is used to protect against smallpox and mpox. To be fully vaccinated people need to have two doses, around four weeks apart.

Why is this research important?

Previous studies have shown the effectiveness of one dose of the Jynneos vaccine against hospitalisation for mpox. But the effectiveness of two doses has not previously been reported on. This is especially important to understand for people with HIV, who have an increased risk of serious illness and death from mpox if they are not virally suppressed.

What did they find out?

Between May 2022 and May 2023, 5,765 people in California got mpox. Of these, 4% were hospitalised. This low level of hospitalisation is likely to be because people had access to vaccination, which began in California in May 2022, as well as treatment.

Around 20% of all people who got mpox were not included in the rest of the study because it was not recorded if they went to hospital or not. Of the remaining 4,353 people, 94% were male and 69% identified as gay, lesbian, or same-gender loving.

Mpox hospitalisation rates were lower among people who had received at least one vaccine dose compared with people who were unvaccinated. This is true for people with and without HIV.

Most mpox infections (83%) happened among people who had not been vaccinated. Around 10% happened among people who had their first does of vaccination after being exposed to mpox, 5% among people who had one vaccine dose but had not been exposed, and 2% among people who had two doses.

Around 6% of people with mpox were hospitalised. Of these, 93% were unvaccinated.

People with HIV accounted for around 40% of mpox infections included in the study, but 56% of mpox hospitalisations. No one with HIV who was fully vaccinated was hospitalised.

Compared with being unvaccinated, people who had a single dose of vaccine were 73% less likely to get mpox (72% for people with HIV), and 80% less likely for two doses. Being vaccinated after being exposed to mpox was less effective at 58%.

What does this mean for HIV services?

People at heightened risk of mpox need access to vaccinations. Getting vaccinated will stop most people from getting mpox, including people with HIV. Those who do get mpox after being vaccinated are far less likely to become seriously ill.

The groups of people who are most at risk of mpox will differ depending on the country. In west and central African countries mpox has been around for years and affects a wider range of people. In Nigeria, for example, about 40% of mpox cases were among women in 2022, compared to only 5% of cases in the USA. However, gay men and other men who have sex with men in Africa are still at heightened risk of mpox. People with HIV are also an at-risk group.

Anyone with HIV who is virally unsuppressed should be prioritised for mpox vaccination, as they are most at risk of getting seriously ill. People with mpox should also be tested for HIV.

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