Mpox vaccine immunity appears to wane within a year – study

Immunity from the mpox vaccine appears to drop off after a few months, according to a small new study.

Using samples from 45 people who were either vaccinated against or infected with mpox in 2022, researchers from Harvard Medical School found that mpox antibodies waned six to 12 months after immunisation.

Two doses – which health authorities recommend four weeks apart – were better than one in the initial months after vaccination.

But a year later, the immune response for people who had two shots was similar to the peak response for those who got just one dose, “which provided limited protection,” according to the study, published in the medical journal JAMA.

The findings indicate that people who were vaccinated during the global mpox outbreak in 2022 may need additional shots to keep up their immunity, according to health experts who were not involved with the study.

“This study suggests that boosters might be required to maintain vaccine effectiveness,” Jonas Albarnaz, a fellow researching virology and immunology at the United Kingdom-based Pirbright Institute, said in a statement.

France already recommends mpox booster shots for people at higher risk of infection, including gay and bisexual men, sex workers, transgender people with multiple sexual partners, and their close contacts.

The new study analysed antibody levels in the weeks and months after vaccination with the Modified Vaccinia Ankara-Bavarian Nordic (MVA-BN) shot, which is the only mpox vaccine approved in the European Union and the UK.

The findings have some caveats.

For example, a decline in antibodies doesn’t necessarily mean that people will be less protected against mpox in real life, according to Jake Dunning, a senior research fellow at the University of Oxford’s pandemic sciences institute and a member of the World Health Organization’s (WHO) mpox emergency committee.

Even with fewer antibodies, the vaccines may have “effectively primed” the immune system to recognise the threat from the virus and quickly fight back, Dunning, who is investigating health workers’ immune responses with the mpox vaccine, said in a statement.

“Vaccines designed to protect people against smallpox and mpox may differ in their ability to stimulate different parts of the immune system, including the parts that have longer-term ‘memory’ functions and protect us if we encounter the pathogen months, years, or even decades later,” Dunning said.

‘Need to understand the level of population immunity’

Bigger studies with more people – including children, pregnant women, and people with HIV, who are at higher risk of poor outcomes if they get mpox – will give researchers a stronger understanding of how well the vaccine works over time.

“To assess the current mpox outbreak risks, we need to understand the level of immunity in the population,” Alexis Robert, a research fellow at the London School of Hygiene and Tropical Medicine, said in a statement.

Health authorities got the global mpox outbreaks under control in 2022 through targeted public health communication, behaviour changes, and access to vaccinations and antiviral treatments for at-risk groups.

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From September 2022 to February 2023, nearly 337,000 mpox vaccines were administered across 25 European countries, and the virus has spread only at low levels since then.

“It is reassuring that nearly two years after the peak of the mpox outbreak in North America and Europe, case numbers have remained low, and post-vaccine infections are rare,” Dr Boghuma Titanji, an assistant professor of medicine at Emory University in the United States, said in a statement.

But mpox is worrying health experts once again because a new strain emerged last year in the Democratic Republic of the Congo (DRC), and cases are spreading across the continent.

More than 26,500 mpox cases and 720 deaths have been reported in Africa this year, and the WHO declared an international health emergency over the outbreak in August.

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Mpox can spread through close contact, including sex, with an infected person. Symptoms include skin lesions, fever, headache, chills, and swollen lymph nodes.

One antiviral drug is available in Europe to treat mpox, but access to vaccines and treatments has been limited in most of Africa.

This summer, an antiviral drug being tested as an mpox treatment failed to improve key symptoms for patients infected with the clade spreading in the DRC.

Given those results, the Pirbright Institute’s Albarnaz said the new vaccine study serves as a “disappointing” call to action to “double down on our efforts” to develop interventions to combat the virus.

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