But that estimate had a wide 95% confidence interval, ranging from 5.0 – 41.0, Mermin noted, and these new findings fall within this window. This most recent analysis used much more data, including the addition of the equivalent of over 1 million person-weeks of follow up. “Even though the point estimate is lower, it is consistent with the prior estimates because of the confidence intervals in the prior study, and because you have additional data that that makes the estimates more precise,” he said.
The new analysis also found that the second dose of the vaccine conferred even more protection: unvaccinated persons were 9.6 times as likely to contract mpox compared with those who had received both doses of the vaccine at least 2 weeks earlier (IRR, 9.6; 95% CI, 6.9 – 13.2). The analysis also suggested there was no difference in efficacy between subcutaneous and intradermal administration of the vaccine.
Wilkin noted that while this data is reassuring, more research is necessary to understand vaccine efficacy between both intradermal and subcutaneous administration routes. There are ongoing studies looking into these questions, he noted. He also emphasized that further studies are necessary to understand vaccine efficacy in immunocompromised populations, like those with uncontrolled HIV. In these populations, mpox infection can be severe and even fatal.
Surveillance Supports Vaccine Safety
From May 22 through October 21 of this year, the Vaccine Adverse Event Reporting System (VAERS) received 1350 reports for the JYNNEOS vaccine, according to a second analysis published today in MMWR. The most commonly reported adverse health event for both subcutaneous and intradermal administration was injection site erythema. For doses given intradermally, other common side effects were dizziness, urticaria, injection site swelling, and syncope. For subcutaneous injections, common reported adverse health events were injection site swelling, injection site pain, pain, and erythema.
Whereas there was no difference in reporting rates for adverse events between intradermal and subcutaneous injection, vaccine administration errors were reported more often for intradermal injections. The most commonly reported error (54% of error reports) was the absence of a wheal after injection; however, Mermin noted that the CDC’s clinical considerations for the use of the mpox vaccine state that a wheal is not necessary for valid administration.
In the past, many clinicians have given intradermal injections for a PPD skin test for tuberculosis, where a wheal was expected, he explained. “I think what’s happened is for many clinicians, they’ve thought a wheal is necessary [for mpox vaccination] because it’s important for the TB skin test, but it’s not so,” Mermin said.
Fourteen reports were classified as serious adverse health events. Nine individuals were hospitalized for myocarditis (two), pericarditis (two), appendicitis (one), aseptic meningitis (one), atrial fibrillation (one), idiopathic thrombocytopenic purpura (one), and methemoglobinemia (one).
There were two deaths reported within 2 days of vaccine administration, in males aged 37 and 58. In one case, the cause of death was listed as drowning, while the death certificate is pending on the other case. Three individuals reported injection site discoloration (one), injection site pain (one), and injection site scar (one) as representing disability or permanent damage. No serious adverse events were reported in persons younger than 18 years.
Although live, replicating smallpox vaccines like ACAM are associated with higher rates of myocarditis, safety data for JYNNEOS suggest no increased risk for myocarditis following vaccination. The VAERS myocarditis reporting rate was seven times lower than what would be expected based on the estimated background rate of condition. “Myocardititis does not seem to be a concern with this vaccine,” Wilkin said.
Vaccination Efforts Remain Vital
With the decline in number of cases, thanks to both vaccination efforts and behavioral changes, federal officials recently announced they plan to let the mpox emergency declaration expire at the end of January. But both Mermin and Wilkin noted that mpox prevention efforts need to be continued to stay ahead of the virus. Communities of color tend to be disproportionally affected by mpox, so higher vaccine coverage is necessary, Wilkin said. “My hope is that this new data will be reassuring to these communities and improve vaccination rates,” he added.
Mermin noted that mpox vaccination should be integrated into HIV and STI clinics as a part of routine care. “We’ll also need to continue vaccine-equity activities by bringing mpox vaccination to communities and venues and events, rather than asking people to come to us to get vaccinated,” he said; “We’re in the fourth quarter and ahead, but the epidemic is not over.”
Mermin and Wilkin report no relevant financial relationships.
MMWR. Published online December 8, 2022. Reduced Risk for Mpox, Safety Monitoring of JYNNEOS