Although monkeypox cases are expected to increase as a result of the national call to clinicians to identify cases, the United States has no surfeit of medical countermeasures. These include two vaccines, a vaccinia immune globulin intravenous product, an antiviral drug, and large testing capacity, said outbreak investigators with the poxvirus and rabies branch at the Centers of Disease Control and Prevention (CDC) in a recent clinical update.
Testing to confirm monkeypox is a two-step process, but results generally are available within a couple of days.
“First, state labs that are part of a laboratory response network can perform orthopox (OPX) generic testing, and this confirms the presence of OPX DNA (deoxyribose nucleic acid) from the rash lesions,” said the CDC’s Agam Rao, MD. “After that, specimens have to be sent to the CDC for confirmatory testing, and that is performed by real-time PCR (polymerase chain reaction), which is only available at CDC. So, a positive test at that step is then called a confirmed monkeypox case.”
Regarding vaccines, one is Jynneos, a live virus vaccine that contains attenuated orthopox virus.
“Jynneos was licensed by the FDA (Food and Drug Administration) in September of 2009 and is indicated for the prevention of smallpox and monkeypox disease in adults 18 years of age and older determined to be at high risk for smallpox or monkeypox virus infection,” said the CDC’s Brett Petersen, MD.
The other vaccine, ACAM2000, contains live vaccina virus but not smallpox virus (variola). It cannot cause smallpox, but its ability to replicate much better than the weakened strain in Jynneos may cause more adverse reactions, Petersen said.
The CDC holds an emergency access investigational new drug protocol that allows the use of ACAM2000 for non-variola orthopox virus infections, which, in this case, is monkeypox. “ACAM2000 does produce a ‘take’ or major cutaneous reaction, which is a vaccine site lesion occurring at the site of inoculation,” he said. “By contrast, Jynneos does not produce any take after vaccination.”
As opposed to Jynneos, there is a risk of inadvertent inoculation and autoinoculation with ACAM2000 from the vaccine site lesion.
“Cardiac adverse events have been reported with ACAM2000, and myopericarditis is expected to occur in up to 5.7 per 1,000 primary vaccines,” he said. “Myopericarditis has not been observed as associated with Jynneos and, as such, the risk is believed to be lower than that for ACAM2000.”
ACAM2000 is administered percutaneously by a multiple puncture technique in a single dose using a bifurcated needle. However, Jynneos is administered subcutaneously in two doses 28 days apart, achieving peak immunity of about 85% two weeks after the second shot. That timeline is not ideal for administering post-exposure prophylaxis (PEP), but Jynneos appears to be the primary vaccine being offered to exposed individuals and healthcare workers because of concerns about the adverse effects of ACAM2000.
“The sooner an exposed person gets the vaccine, the better,” the CDC states. “CDC recommends that the vaccine be given within four days from the date of exposure in order to prevent onset of the disease. If given between four and 14 days after the date of exposure, vaccination may reduce the symptoms of disease, but may not prevent the disease.”
Jynneos also is recommended for pre-exposure vaccination in laboratorians who work with orthopox viruses and designated members of emergency response teams.
In terms of monkeypox treatment options, tecovirimat is an antiviral medication approved by the FDA for the treatment of human smallpox disease in adults and pediatric patients weighing at least three kilograms, Petersen said. “Oral capsule and IV (intravenous) formulations were approved by the FDA in July 2018 and May 2022, respectively.”
A CDC emergency access investigational new drug protocol allows the use of tecovirimat for non-variola orthopox virus infections, such as monkeypox.
“This protocol also includes allowance for opening an oral capsule and mixing its contents with liquid or soft food for pediatric patients weighing less than 13 kilograms,” he said.
The CDC is developing treatment guidelines for monkeypox, which often is self-limiting in the absence of any therapy. “But the prognosis for monkeypox may depend on multiple factors, such as previous vaccination status, initial health status, and concurrent illnesses or comorbidities,” Petersen said.
Underlying conditions that may undermine monkeypox recovery include sepsis, encephalitis, pregnant or breastfeeding women, bacterial skin infections, and gastroenteritis. Thus, patients in this group may be administered tecovirimat based on clinical judgement and consultation with the CDC.
“Vaccina immune globulin is an intravenous product licensed by the FDA for the treatment of complications due to vaccinia vaccination, including eczema vaccinium, progressive vaccinia, and severe generalized vaccinia,” Petersen said.
Although monkeypox cases are expected to increase as a result of the national call to clinicians to identify cases, the United States has no surfeit of medical countermeasures. These include two vaccines, a vaccinia immune globulin intravenous product, an antiviral drug, and large testing capacity.
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