Transparency and monitoring of side effects will be particularly important in addressing vaccine concerns. The Jynneos vaccine, which looks to be about 85 percent effective against monkeypox, was approved based on animal studies and limited studies in humans. So far, it has been rolled out among certain populations, like members of the military and some laboratory researchers, with no apparent safety concerns.
“I think the benchmark that they used was reasonable,” Omer said of the vaccine trials. “So far, the safety record has been reasonable. But we need to again weigh the need versus the side effects.” The Jynneos vaccine doesn’t leave a scar like the earlier pox-family vaccine that was widely used against smallpox does, but it can be unpleasant to receive—with redness and swelling at the injection site alongside fever, fatigue, nausea, and chills. There is also little data on vaccination during pregnancy, although some countries, like the U.K., have begun vaccinating pregnant people during this outbreak, given the risks of contracting monkeypox during pregnancy and no adverse effects in animal trials. In addition, the vaccine isn’t approved for children under the age of 18, and it has not been studied well in this population.
The vaccines currently being administered “should come with a robust postmarketing surveillance program” for effectiveness and safety in a wider population, Omer added. With the earlier smallpox vaccine, pericarditis and myocarditis soon emerged as potential side effects—in fact, that’s one of the reasons researchers looked for these conditions after Covid vaccination. So far, the very rare side effect doesn’t seem to have been detected with the later smallpox vaccines, but monitoring those who receive them now could help understand the vaccines’ safety profile.