Jynneos vaccine offers ‘substantial’ protection against mpox, studies find
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Key takeaways:
- The Jynneos vaccine was up to 86% effective against mpox when people received two doses.
- U.S. public health officials are concerned about an mpox outbreak this summer.
The Jynneos vaccine was up to 86% effective at preventing mpox in people who received two doses during the United States outbreak, according to three studies published Thursday.
The studies showed that one dose of the vaccine also reduced the risk for mpox, including one study published in MMWR in which the effectiveness of a single dose was 75%. A second study in MMWR reported a combined effectiveness of around 76% for one or two doses among people who received the vaccine in New York.
A larger study, published in The New England Journal of Medicine, found that two doses of the vaccine were 66% effective, and one dose was 36% effective. Previous studies of the Jynneos vaccine also found that it protects against mpox.
“What we take away from these studies is that the vaccine’s effectiveness is substantial,” Christopher R. Braden, MD, the CDC’s mpox response incident manager, said during a call with reporters. “Being vaccinated will help decrease the spread of mpox in populations, it will help individuals prevent acquisition of mpox and it will help individuals avoid severe disease or even death.”
Braden said the studies have different results because they used different data sources — for example, the first MMWR study relied on voluntary responses and The New England Journal of Medicine study also included immunocompromised people, who are more likely to acquire a breakthrough case of mpox. Braden said “we still don’t know enough about the effectiveness of this vaccine in the population of immunocompromised persons.”
“We need the different types of studies looking at data in different ways to come up with a combined estimate that looks across these studies,” he said, adding that “each of the estimates is within the confidence interval of each individual study so, statistically, there is not all that much difference.”
It has been around a year since the global mpox outbreak began to widen. Months into the U.S. outbreak, the FDA authorized fractional dosing of the Jynneos vaccine because of shortages and based on smaller trials that found that one-fifth-sized doses were effective.
The larger MMWR study enrolled 309 patients who had been diagnosed with mpox and 608 controls between Aug. 19, 2022, and March 31, 2023, in a matched case-control study. All participants self-identified as men who have sex with men (MSM) or as transgender, and agreed to complete a survey either online or by telephone.
Alexandra F. Dalton, PhD, and colleagues found that one dose was 75% effective against mpox (95% CI, 61.2%-84.2%) and receiving a second dose increased the effectiveness to 86% (95% CI, 73.8%-92.4%).
In The New England Journal of Medicine case-control study, researchers used electronic health records to analyze data on 2,193 patients with mpox and 8,319 control patients. Of these, 25 patients and 335 controls had been fully vaccinated, and 146 case patients and 1,000 controls were partially vaccinated.
According to Nicolas P. Deputy, MD, and colleagues, two doses were 66% effective (95% CI, 47.4%-78.1%) and one dose was 35.8% effective (95% CI, 22.1%-47.1%)
The CDC this week issued a health alert about the potential risk for mpox outbreaks this summer after Chicago reported more than a dozen new cases — most among people who are fully vaccinated.
“There are a number of possible explanations,” Demetre Daskalakis, MD, White House national mpox response deputy coordinator, said during the call.
“We don’t know if immunity after vaccination fades with time,” but there are ongoing studies examining the concern, he said.
Daskalakis said the White House and CDC have continued the outreach programs they started in August 2022 to increase mpox awareness among MSM and vaccinate people. The plan, he said, is to increase this outreach because there is “substantial risk” for an outbreak this summer.
“Vaccination makes getting and spreading mpox less likely, and may decrease the chances of severe illness, hospitalization or death — even if it doesn’t prevent infection,” Daskalakis said. “The more immunity we have in the community, the lower the chance there is that there will be an outbreak.”
References:
- Dalton AF, et al. MMWR Morb Mortal Wkly Rep. 2023;doi:10.15585/mmwr.mm7220a3.
- Deputy NP, et al. N Engl J Med. 2023;doi:10.1056/NEJMoa2215201.
- Rosenberg ES, et al. MMWR Morb Mortal Wkly Rep. 2023;doi:10.15585/mmwr.mm7220a4.
Perspective
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These studies suggest that two doses of the mpox vaccine are more effective in the real world compared with one dose, although one dose provides very good protection. The study reported in MMWR presents higher vaccine effectiveness compared with the one published in The New England Journal of Medicine. Some of this may be due to study design differences and the fact that the MMWR timeline spans from the peak of the outbreak in August 2022 to March 2023. During that time, transmission was already slowing down.
Nevertheless, the results highlight the importance of individuals most at risk for exposure getting at least one dose — preferably two doses — of vaccine. This is a task that our public health and health care systems are simply not equipped for because we don’t have long-term resources to support health departments and because health care is just too expensive for many individuals in our country, particularly those who belong to minoritized populations.
Because health departments have lost pandemic-related resources over the last year, they have gone back to putting out fires with very limited staff. Even with dwindling public health resources, getting one dose to those who need it can eventually happen (probably after the peak of an epidemic because it takes an unnecessarily long time to convince the powers that be to mobilize resources.) But getting two doses remains a tall order given the realities of our health-related systems. Furthermore, those who are most vulnerable to infection are the ones with the fewest resources and are the hardest to reach. The MMWR article highlights that more homeless individuals, individuals with HIV and those engaging in transactional sex were infected with mpox compared with individuals who were not facing these realities.
Yes, it is hopeful to read that we have effective vaccines that can help reduce the burden of mpox among already vulnerable populations when the next mpox outbreak begins. We can even consider preemptively providing mpox vaccines to high-risk populations before the next mpox outbreak. But this should also be a time to meet the challenge of establishing stable and well-resourced public health and health care systems for all.
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