Intradermal administration of the JYNNEOS mpox vaccine is as effective and safe as subcutaneous administration, according to new data released this week by the Centers for Disease Control and Prevention (CDC).
Unvaccinated people were nearly 10 times more likely to contract mpox than those who completed the two-dose vaccine series, and the rate of adverse health event reporting is similar for both routes of administration.
“There has been some hesitancy about intradermal vaccination, so I think these data are very reassuring,” Timothy Wilkin, MD, an infectious disease specialist at Weill Cornell Medicine in New York, told the Medscape Medical News. He was not involved in the research.
JYNNEOS, a vaccine to protect against smallpox and monkeypox, was approved by the US Food and Drug Administration in 2019 and has traditionally been administered subcutaneously. In August, the FDA issued an emergency use permit for intradermal dosing of the vaccine to help expand the supply of the sought-after vaccine.
Since the beginning of the mpox outbreak in May, 29,711 cases have been reported in the United States and more than 1.1 million doses of JYNNEOS mpox vaccine have been administered. Mpox incidence in the U.S. has dropped more than 95% since the peak of the outbreak in July, said Jonathan Mermin, MD, MPH, director of the CDC’s National Center for HIV, Viral Hepatitis, STD, and TB Prevention. There are currently fewer than 10 new cases in the US each day.
Mermin told Medscape that both behavioral changes to mitigate the spread of the virus and vaccination led to this large reduction, but he also noted that better access to mpox testing and vaccination for the communities most affected by the epidemic — gay and bisexual men and transgender people. — is essential to sustain progress. “If these efforts do not continue, the declines could be reversed and we could find ourselves responding to a resurgence of infection,” he said.
Vaccination protects against Mpox infection
The CDC collected data from 43 jurisdictions between July 31 and October 1 of this year to estimate overall vaccine effectiveness. The analysis, published today in the CDC Morbidity and Mortality Weekly Report (MMWR), included 9544 reported cases of mpox in men aged 18-49 years. Of these cases, 87.2% were among unvaccinated individuals. Of mpox cases in vaccinated individuals, 61% were in people whose illness began 13 days or less after a single dose of the vaccine. Of the 39% (392 cases) whose disease occurred at least 2 weeks after the initial dose, the majority (295) occurred before the individual received the second dose. Only 0.5% of all mpox cases (48) were in people who were fully vaccinated – when the disease started at least 2 weeks after the second dose.
The researchers calculated that the average incidence of mpox was 7.4 times higher in unvaccinated persons than in those who had received a single dose of mpox vaccine at least two weeks earlier (incidence ratio [IRR], 7.4; 95% CI, 6.0 – 9.1). That’s less than estimates from an earlier CDC analysis that suggested unvaccinated individuals were, on average, 14 times more likely to contract mpox than those who received a single dose of the vaccine.
But that estimate had a wide 95% confidence interval ranging from 5.0 to 41.0, Mermin noted, and these new findings fall within that window. This latest analysis used much more data, including adding the equivalent of more than 1 million person-weeks of observation. “Even though the point estimate is lower, it’s consistent with previous estimates because of the confidence intervals in the previous study and because you have additional data that makes the estimates more precise,” he said.
The new analysis also found that the second dose of the vaccine provided even greater protection: unvaccinated subjects were 9.6 times more likely to develop mpox compared with those who received both doses of the vaccine at least 2 weeks earlier (IRR, 9.6; 95% CI, 6.9 – 13.2). The analysis also indicated that there was no difference in efficacy between subcutaneous and intradermal administration of the vaccine.
Wilkin noted that while these data are reassuring, more research is needed to understand the efficacy of the vaccine between the intradermal and subcutaneous routes. Studies are underway to address these questions, he noted. He also stressed that further studies are needed to understand the effectiveness of the vaccine in immunocompromised populations, such as those with uncontrolled HIV. In these populations mpox infection can be severe and even fatal.
Surveillance promotes vaccine safety
According to a second analysis published today MMWR. The most frequently reported adverse health effect for subcutaneous and intradermal administration was erythema at the injection site. For intradermal doses, other common side effects were dizziness, urticaria, injection site swelling, and syncope. For subcutaneous injections, commonly reported adverse health effects were injection site swelling, injection site pain, pain and erythema.
While there was no difference in the rate of adverse event reporting between intradermal and subcutaneous injection, vaccine application errors were reported more frequently with intradermal injection. The most frequently reported error (54% of error reports) was the absence of pimples after the injection; however, Mermin noted that the CDC’s clinical considerations for use of the mpox vaccine state that a pimple is not necessary for valid administration.
In the past, many clinicians administered intradermal injections for the PPD tuberculosis skin test where bruising was expected, he explained. “I think what happened is for many doctors who thought that a blow was necessary [for mpox vaccination] because it’s important for the TB skin test, but it’s not,” Mermin said.
Fourteen reports were classified as serious adverse health events. Nine subjects were hospitalized for myocarditis (two), pericarditis (two), appendicitis (one), aseptic meningitis (one), atrial fibrillation (one), idiopathic thrombocytopenic purpura (one), and methemoglobinemia (one).
Two deaths were reported within 2 days of vaccine administration, in men aged 37 and 58 years. In one case, the cause of death was given as drowning, in the other, a death certificate is pending. Three subjects reported injection site discoloration (one), injection site pain (one), and injection site scarring (one) as manifestations of disability or permanent damage. No serious side effects have been reported in people under 18 years of age.
Although live, replicating smallpox vaccines such as ACAM are associated with higher rates of myocarditis, safety data for JYNNEOS do not indicate any increased risk of myocarditis following vaccination. The VAERS reporting rate of myocarditis was seven times lower than would be expected based on the estimated base rate of the disease. “Myocarditis does not appear to be a concern with this vaccine,” Wilkin said.
Vaccination efforts remain essential
With the number of cases falling, thanks both to vaccination efforts and behavioral changes, federal officials recently announced plans to let the mpox emergency expire at the end of January. But both Mermin and Wilkin noted that mpox prevention efforts must continue to stay ahead of the virus. Communities of color tend to be disproportionately affected by mpox, so higher vaccine coverage is essential, Wilkin said. “I hope this new data will be reassuring to these communities and improve vaccination coverage,” he added.
Mermin noted that mpox vaccination should be incorporated into HIV and STI clinics as part of routine care. “We will also need to continue our vaccine justice activities by bringing mpox vaccination into communities, places and events instead of asking people to come to us to get vaccinated,” he said; “We are in the fourth quarter and ahead, but the epidemic is not over.
Mermin and Wilkin report no relevant financial relationships.
MMWR. Published online Dec 8, 2022 Mpox Reduced Risk, Safety Monitoring JYNNEOS
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