The independent vaccine advisers to the US Centers for Disease Control and Prevention voted unanimously Wednesday in favor of the two-dose Jynneos mpox vaccine for adults at risk of catching the disease during an outbreak.
If the CDC agrees with the committee’s recommendation, there will be a recommendation in place to give the vaccine to people who are at risk for mpox during future outbreaks.
The number of new cases of mpox, formerly known as monkeypox, has fallen significantly in the US since the peak of the most recent outbreak in August. The current seven-day average shows that there are still two new cases a day, compared with about 450 cases a day in August – but two cases is higher than the US has had in previous years, the experts said.
“We have a very effective vaccine,” said committee member Dr. Jamie Loehr, owner of Cayuga Family Medicine in Ithaca, New York. “We’ve got good data.
“And it’s actually got a fairly high death rate if I’m doing my math correctly. It’s about 1 in 1,000, and that’s not an insignificant death rate. So I’m very much in favor of this,” Loehr added.
The 18 members voted in favor of the vaccine recommendation: “ACIP recommends the 2-dose Jynneos vaccine series for persons aged 18 years and older at risk of mpox during an mpox outbreak.”
In 2021, the committee voted in favor of the Jynneos vaccine for people with occupational risks of virus exposure. In August, during the height of the outbreak, the vaccine got emergency use authorization to help prevent further illness.
More than 1.18 million Jynneos vaccines have been administered in the US, according to the CDC.
Although the effectiveness of the vaccine was never demonstrated in clinical trials for mpox, studies during the outbreak showed that it was up to 83% effective, the CDC said. Still, more data is needed to fully understand how well it works in people with underlying health issues that leave them with weakened immune systems.
Mpox incidence among unvaccinated people was 7.4 times as high as in those who’d gotten one dose of Jynneos vaccine and 9.6 times as high as in those who’d gotten two doses of Jynneos vaccine, according to a CDC presentation.
There were no new or unexpected safety concerns with the vaccine, according to the CDC presentation. Serious adverse events among adults were rare. There was no indication that the vaccine raised the risk of myocarditis or pericarditis. The most common complaints were redness at the injection site and fatigue.
Even as mpox cases continue to fall, the CDC is encouraging people who are at risk to get vaccinated.
“We do not think that this outbreak is over, and that’s very important to keep in mind,” said Dr. Agam Rao, medical officer in the CDC’s Division of High Consequence Pathogens and Pathology.
There’s also a possibility of future outbreaks, she said.
“There’s actually been a re-emergence of human cases after decades of no reported cases in some countries,” Rao added.
The US led the world in mpox cases during the most recent outbreak, with more than 30,000 illnesses and cases in all 50 states. The people most at risk were members of the gay and bisexual community and other men who have sex with men, who accounted for 95% of cases. Overall cases were primarily reported among Black, Hispanic and White people, with nearly a third of cases in each group.
Mpox also seemed to spread mostly through people who were sexually active. Of cases in which the CDC had information on sexual history, 75% reported having sex or close contact with another person three weeks prior to symptoms starting, and 25% reported no sexual contact, according to the CDC.
Mpox is no minor infection. Pain has been “particularly pronounced” with lesions, Rao said. Lesions on the eye can cause blindness. There can also be neurological complications and brain swelling. The most severe manifestations of mpox, including uncontrolled viral spread, were among people who had severely weakened immune systems.
The disease was rarely fatal, but there were 32 deaths, representing 0.1% of mpox cases, primarily in people who were severely immunocompromised.
The CDC said the committee will meet again in June to consider recommending the vaccine for people who are younger than 18. In October, the committee will consider a longer-term vaccine strategy.
“The recent outbreak has highlighted again the risks that infectious diseases can present to our communities, the importance of a robust public health response at the state and local level, the value of engaged partners and communities in responding to public health threats and the impact that a vaccine can have in helping to bring an outbreak under control,” said CDC Associate Director for Vaccine Policy Dr. Melinda Wharton.