Antibodies from the mpox vaccine Jynneos appear to drop off after a few months, and boosters may be needed, according to a small new study.
Researchers from Harvard Medical School found that mpox antibodies waned six to 12 months after immunisation, but that more research is needed to confirm this.
Last month, Te Whatu Ora reported 11 mpox cases in NZ linked to a Queenstown festival.
The SMC asked experts to comment.
Massimo Giola, President of the Australasian Sexual Health Medicine Committee of the Royal Australasian College of Physicians, comments:
“We have known for a while that the level of antibodies was going to drop over time after vaccination.
“But antibodies are not the only indicator of protection. There is also cellular immunity, which is extremely important for the protection against viruses.
“We also have had evidence that smallpox vaccines were protecting against mpox. Mpox only started to spill over from animals to humans in Africa after the universal smallpox vaccination was stopped.
“We are seeing internationally and even in the latest outbreak in New Zealand, cases of mpox among people who got the two doses of Jynneos vaccine. So it’s going to be a situation very much like the vaccine for Covid that essentially, particularly with the new variants, the vaccine doesn’t give you protection against infection. But it gives you protection against severe infection and death. So the cases of mpox among people who have had the vaccine are less severe and not leading to any serious consequences.
“Therefore, even with study, it is crucial for people at risk to get two doses of the vaccine. That includes people who are immunosuppressed, or who have conditions potentially leading to immune suppression, such as those living with HIV, or people with cancer.
“There are no plans at the moment for further boosters, so watch the space if more evidence comes through.
“Finally the number of cases in New Zealand are so small that any detailed information such as geographical location can become identifiable. That is probably why public health officials are very careful about communicating the data.”
No conflict of interest declared.
Associate Professor Helen Petousis-Harris, Medical and Health Sciences, University of Auckland, comments:
“After MPOX vaccination, the immune response includes both humoral and cellular immunity. Humoral immunity involves the production of neutralising antibodies that initially rise but may decline over time. Cellular immunity, particularly through memory B and T cells, is crucial for long-term protection, enabling the immune system to reactivate antibody production and other immune responses when encountering the virus again. Together, these systems work to prevent severe disease, even as antibody levels decrease.
“This study measures the decline in antibodies measured in the blood after vaccination with Mpox vaccine. Understanding the dynamics of antibody decline is one important component that helps us understand the nature of immunity from this vaccine.
“What the study does not tell us is if this correlates to waning protection against disease, particularly severe disease. To know this we need to conduct different sorts of studies that look at mpox infections in vaccinated and unvaccinated people over time.
“Even if antibodies in the blood has waned a person may have long lived immune memory that can be rapidly triggered on re-exposure to either a vaccine or natural infection. The incubation period for Mpox is actually quite long giving plenty of time for immune memory to kick in. We do not yet know the real-life duration of protection offered by this vaccine. This will take a little more time.
“While there have been cases of Mpox reported in people who have been vaccinated, like with many other vaccines, data to date indicate the breakthrough infections can be less severe.
“This study is but one important piece of information about this Mpox vaccine. I am not convinced we have enough information about duration of protection to be recommending boosters of a globally precious resource at this stage.”
No conflict of interest declared.
Becky Jenkins, Director, Protection, National Public Health Service, comments:
“As of today (Friday 4 October) there have been 11 confirmed cases of mpox that are linked to the Queenstown Winter Pride Festival. All are being supported by NPHS and Sexual Health Services as needed.
“There have been 17 cases of mpox confirmed in New Zealand to date since the start of 2024, and 66 confirmed cases since reporting began in July 2022.
“While it is possible that other cases may yet be confirmed, it’s important to remember that mpox is a rare infection and the risk of it spreading widely in New Zealand remains low.
“Anyone who thinks they may have been exposed to mpox, or who develops symptoms, especially a rash, should seek medical advice.
“As the mpox virus can spread through close contact (including intimate / sexual contact) with a person with mpox, we also strongly urge anyone with symptoms to refrain from sexual activity and seek support.
“People should contact their nearest sexual health clinic, GP or healthcare professional, or call Healthline on 0800 611 116 for advice and support.”
Alana Ewe-Snow, Director, Prevention, National Public Health Service, comments:
“Vaccines are important for both preventing disease and reducing the severity of disease if a person does get infected. Regardless of whether the protection against developing disease is shown to decline over time, it is likely that the vaccination will still provide protection in reducing severity or likelihood of infecting others.
“It’s important to note that the study published in JAMA mainly looked at antibodies, which are only one component of the immune system response. Clinical and epidemiological studies in humans are required to show any changes in levels of vaccine protection. We don’t yet know whether antibodies are a reliable predictor of overall immunity.
“Previous studies have shown that mpox vaccine effectiveness is around 78%, and it is not yet clear how much this wanes over time in the real world.
“While vaccination is an important part of our strategy to control mpox in Aotearoa New Zealand, we are also working closely with affected communities to ensure they understand the disease and other measures that can reduce the risk of spread.
“Health New Zealand | Te Whatu Ora and The Ministry of Health | Manatū Hauora will continue to monitor the emerging evidence on mpox vaccine effectiveness.”
Our colleagues at the UK Science Media Centre also gathered comments:
Dr. Alexis Robert, Research Fellow at the London School of Hygiene and Tropical Medicine, comments:
“This new research letter from Collier et al shows that Mpox antibody response declined with time since vaccination in 47 individuals vaccinated with the modified vaccinia Ankara–Bavarian Nordic. The antibody level after one year was back to the pre-vaccination levels for some of the Mpox antigens. The Mpox outbreak declared in the United Kingdom in 2022 was brought into control through declines in transmission rate from behavioural changes, and targeted vaccination of at-risk groups. The waning highlighted by Collier et al is therefore important to investigate, especially since vaccination of high-risk group was credited for reducing the risk of Mpox resurgence since 2022 (Brand et al, 2023).
“Mpox is an infectious disease associated with severe illness. To assess the current Mpox outbreak risks, we need to understand the level of immunity in the population. As highlighted by the authors, the study uses a limited sample size (25 1-dose recipients, 22 2-dose recipients), so the results need to be confirmed with larger, more representative samples, to get a full picture of the level of protection in the vaccinated population. In such a small sample, the effect of individual features cannot be analysed: for instance, the age at vaccination, or medical history could impact the response of individuals. Future analyses with larger sample size should identify factors that contribute to this decrease, so we better understand what it means for the level of immunity in the population.
“Finally, antibody concentration will need to be connected to infection risks through epidemiological investigations. This will show how vaccinated individuals contribute to outbreaks: are they as likely be infected as unvaccinated individuals? Are their symptoms milder? Are they as likely to transmit? If so, catch up campaigns may be needed to bring transmission risk down, and control Mpox outbreaks.”
No conflict of interest.
Dr. Boghuma Titanji, Assistant Professor of Medicine, Emory University, comments:
“This study is crucial as it examines individuals who received one or two doses of the MVA-BN vaccine or recovered from an mpox infection. The authors found that vaccine-induced neutralizing antibodies and T-cell responses declined significantly within 6-12 months. This raises concerns that previously vaccinated individuals may become more susceptible to mpox as their immunity wanes, suggesting that additional booster doses could be beneficial. Some countries, like the United Kingdom, are already recommending booster doses, though other nations have not yet updated their vaccination guidelines accordingly.
“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. This suggests that immunity might not be solely dependent on antibody levels and that other immune factors not yet defined could still offer protection. While the findings need confirmation in larger cohorts including representation of key groups like pregnant people and children, they are important for guiding future vaccination strategies, especially for vulnerable groups at higher risk of exposure.
“Additionally, special attention must be given to understanding vaccine responses and immunity durability in immunocompromised individuals, such as those with HIV. This group is particularly vulnerable to severe mpox and poor outcomes, highlighting the need for tailored vaccination guidelines to protect them effectively.”
No conflict of interest.