Mpox vaccine triggers equally strong immune response in smaller doses
A new study suggests this strategy could help ensure access to immunisation when supplies of mpox vaccine are limited.
- 15 December 2023
- 4 min read
- by Linda Geddes
Delivering smaller than usual doses of mpox vaccine between layers of the skin triggers equally strong immune responses – including in people with HIV. Such a strategy, known as dose sparing, could help to stretch out limited vaccine supplies and ensure that all high-risk individuals can access immunisation during outbreaks.
In May 2022, an outbreak of mpox rapidly cascaded into a public health emergency of international concern as the virus began to spread to countries where it had never previously been detected. The outbreak triggered a surge in demand for the Jynneos smallpox vaccine – which has been approved for mpox prevention – as mpox infection can occasionally be life-threatening.
A new study has confirmed that this strategy prompts an equally strong immune response – including in people whose immune systems are compromised because of HIV infection.
Wealthy countries rapidly bought up as many doses as they could to immunise their high-risk populations, while those living in lower-income countries were forced to join the back of the queue. Even in the US, supply shortages prompted the introduction of a dose-sparing strategy, whereby, rather than getting a full dose of the vaccine injected into the fatty tissue below the skin (subcutaneous administration), people were offered a fifth of the usual dose injected close to the surface of the skin (intradermal administration) – with the two doses spread out by as far as three months apart, rather than the usual four weeks.
Now, a new study has confirmed that this strategy prompts an equally strong immune response – including in people whose immune systems are compromised because of HIV infection. This is important because people living with advanced HIV and weakened immune system are at greater risk of more severe mpox disease and clinical outcomes.
Dr Angelica Kottkamp and colleagues at the NYU Grossman School of Medicine in New York, studied 145 New Yorkers who either received the Jynneos vaccine through intradermal or subcutaneous administration, or a combination of the two. Most were men (81%), and almost all (89%) self-identified as being LGBTQ+. A quarter of them were people living with HIV.
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The study, published in the New England Journal of Medicine, found that people who were fully vaccinated with two one-fifthdoses had an immune response four times stronger than those who had one regular dose and did not complete the vaccination series. And their immune responses were similar to those who received two regular doses injected below the skin.
"Implementing the smaller dose was a good emergency measure in the face of immediate shortages of the vaccine," Kottkamp said.
In some individuals, vaccine-induced antibodies were detected more than six months after a second and final dose of the vaccine. Further studies are needed to determine whether booster vaccination may be needed for longer-term immunity, and how antibody levels correlate with vaccine protection, the researchers said.
The amount of emergency stockpiles of mpox vaccine and/or the ability to ramp up vaccine production quickly in case of future outbreaks also need to be examined, said study senior investigator Prof Mark Mulligan, also at the NYU Grossman School of Medicine.
The study also found that people who had previously been vaccinated against smallpox, as part of routine childhood vaccination programmes, had a stronger immune response than those with no previous smallpox vaccination. And it found no difference in the magnitude of the immune response between vaccinated people living with HIV with a CD4 count above 200 – an indicator of good immune function for an HIV-positive person – and those who were HIV-negative.
"Our findings offer valuable support to the people most at risk of being infected with mpox that in the case of an mpox resurgence, infectious disease specialists have sufficient vaccination tools and knowledge to deal with it effectively in the short term," said Mulligan.
The research provides reassurance that this dose-sparing strategy, or even other strategies such as delaying the second dose, could be potentially considered as a way to stretch vaccine supply. An outbreak of a mpox strain more severe than the one that caused the global outbreak last year currently ongoing in the Democratic Republic of the Congo, with nearly 13,000 suspected cases and some 600 deaths, has provoked concern that it could spread more widely – although cases remain confined to DRC for now.
