The Jynneos vaccine from Bavarian Nordic A/S (OMX:BAVA), the most widely used vaccine to protect against monkeypox, tends to have generally mild side effects according to clinical trial data.
It is also clear that the Jynneos vaccine can help reduce the severity of monkeypox infections. Researchers are uncertain, however, about how the vaccine’s potential to reduce transmission, how strong its protective effect is, or how long it lasts.
A small study in Africa from 1988 found that an older smallpox vaccine was 85% effective in protecting against monkeypox.
CDC notes that there are no data about the effectiveness of the Jynneos or the ACAM2000 vaccine from Emergent Biosolutions (NYSE: EBS) in the current outbreak. The latter vaccine has not found widespread use in the monkeypox outbreak and generally is not as well tolerated as the Jynneos vaccine.
The monkeypox virus can often have significant symptoms. In addition to painful rashes, the virus can cause flu-like symptoms such as fever, chills, exhaustion and respiratory symptoms, such as sore throat, congestion or cough. According to the CDC, the symptoms generally appear within three weeks after exposure to the virus.
Bavarian Nordic evaluated the safety of Jynneos in individuals who had not received a prior smallpox vaccine in a U.S.-based randomized, double-blind, placebo-controlled study. In the study, 3003 individuals between 18 and 40 received two doses of the vaccine, while 1002 individuals received two doses of a saline solution. The doses were administered four weeks apart.
According to the FDA packaging insert for Jynneos, the side effects related to the vaccine include the following:
Pain, redness and swelling at the injection site
In healthy adults who have never received a smallpox vaccine, 84.9% had injection site pain, according to the package insert for Jynneos. A total of 60.8% had redness at the site, while 51.6% had swelling.
In most cases, pain was mild or moderate in intensity.
In addition, 45.4% of Jynneos recipients had induration at the injection site, which refers to a local hardening of soft tissue. Nearly as many, 43.1%, had itching.
Healthy adults who had received a previous smallpox vaccine tended to commonly experience injection site reactions. A total of 80.9% had redness, while nearly as many, 79.5%, had pain at the site. A total of 70.4% had induration at the injection site, and 67.2% had swelling.
The Vaccine Adverse Event Reporting System (VAERS) database paints a similar picture. Injection site erythema and swelling are among the most common adverse reactions reported. As of September 2, however, the most common adverse reaction sited is “incorrect route of product administration,” which has been reported 93 times out of a total of 1,478 events. Additionally, there were 19 reports of the product administered at an inappropriate site.
While the VAERS database is helpful for researchers, its information doesn’t necessarily indicate that a vaccine causes a given adverse event.
Presently, there are limited data in the database for the Jynneos vaccine.
But CDC notes that side effects such as injection site pain and redness are generally among the most common vaccine side effects.
Muscle pain, headache and fatigue cited common monkeypox vaccine side effects
These three adverse events were common. A total of 42.8% of vaccine naive individuals had muscle pain, according to the Jynneos package insert. Approximately one-third, 34.8%, had a headache, while 30.4% had fatigue.
Fatigue and headache were also commonly reported symptoms in the VAERS database.
Such symptoms are also common for vaccination, generally, and for immune activation. In addition, sick animals and humans exposed to bacterial and viral pathogens have similar symptoms, according to a 2013 article in the Journal of Experimental Biology.
In addition to rashes, monkeypox itself can cause headaches, fever, chills and muscle aches.
Less common monkeypox vaccine side effects: Nausea, chills and spreading the vaccinia virus
According to the package insert for the Jynneos vaccine, fewer than one in five people who hadn’t received a prior smallpox vaccine (17.3) had nausea. A total of 10.4% had chills.
Nausea and chills are both common side effects of COVID-19 vaccines, the CDC notes.
The packaging insert for Jynneos notes that the median duration of adverse events associated with the vaccine lasted between 1 and 6 days.
In general, adverse events for individuals infected with HIV were similar to those in healthy adults.
Individuals with severe allergic reactions to gentamicin, ciprofloxacin, egg protein or benzonase are contraindicated from receiving the vaccine, given a risk of anaphylaxis.
CDC also notes that, rarely, individuals vaccinated with the Jynneos vaccine may spread “the vaccinia virus by touching the vaccination site and then touching another part of the body or another person.” Such transmission often occurs after touching the vaccine site and then the genitals or face. When the virus comes into contact with the eyes, it may result in damage to eyesight.
Rare life-threatening reactions
CDC recently has updated a factsheet on smallpox vaccination side effects, estimating that between 14 and 52 people out of on million who received the vaccine for the first time may have potentially life-threatening reactions. Such reactions could include serious rash resulting from severe skin infection in individuals with prior eczema or atopic dermatitis.
Individuals with a weakened immune system may rarely have a buildup of inflamed tissue surrounding the vaccination site. This swelling may expand into a large, non-healing sore known as progressive vaccinia.
In addition, individuals with a weakened immune system or certain skin conditions may be at risk for at type of brain inflammation known as postvaccinal encephalitis.
CDC estimates that between 1 to 2 people out of 1 million people who receive a smallpox vaccine may die as a result of life-threatening vaccine complications.
Infection with the monkeypox virus is more dangerous. The recent case fatality ratio for the virus has been around 3–6%, according to the WHO.
This article was updated on September 13 to include new information.
Filed Under: Infectious Disease