'ACIP Backs Virus-Like Particle Chikungunya Vaccine for Travelers, Lab Workers'

 The CDC's Advisory Committee on Immunization Practices (ACIP) unanimously recommended that U.S. travelers ages 12 years and older receive the virus-like particle chikungunya vaccine (Vimkunya) when they travel to a country or territory with a chikungunya outbreak.

ACIP also unanimously backed a recommendation that this vaccine be considered in that same age group when traveling to or residing in a country or territory that isn't experiencing an outbreak but that poses an elevated risk for those planning to stay for at least 6 months.

In a separate unanimous vote, the committee recommended the vaccine for laboratory workers who potentially could be exposed to chikungunya virus. The panel agreed that vaccination isn't necessary for lab workers who handle routine clinical samples.

The virus-like particle chikungunya vaccine received accelerated approval from the FDA in February, and is one of two single-dose vaccines to prevent disease caused by the chikungunya virus. During a meeting last year, ACIP made recommendationsopens in a new tab or window on the use of the live-attenuated chikungunya vaccine (Ixchiq), which received accelerated approvalopens in a new tab or window in November 2023.

The chikungunya virus is widespread in tropical and subtropical regions. Infected mosquitoes spread the virus to people, triggering outbreaks that can be large and explosive. Fever and joint pain are the most common symptoms, but infection can also trigger muscle pain, headaches, rash, or joint swelling. There are no FDA-approved treatments for chikungunya infection. Although severe illness isn't common, infection can be fatal, primarily in infants and older adults.

During the meeting, ACIP also reviewed safety data from the Vaccine Adverse Event Reporting System (VAERS) that included six serious adverse events, including hospitalization, after vaccination with the live-attenuated vaccine. All six events occurred in people older than age 65 years who had multiple comorbidities, such as hypertension, hyperlipidemia, coronary artery disease, or diabetes.

These data and other post-licensing safety information prompted ACIP to revise age-related language in its earlier recommendations for the live-attenuated vaccine for those traveling to places without an active outbreak but with an elevated risk of one.

The updated ACIP recommendations are unchanged in their support for the live-attenuated vaccine in people ages 18 years and older who travel to a country or territory with a chikungunya outbreak. This vaccine may also be considered in that age group when a person travels to or resides in a country or territory that isn't experiencing an outbreak but that poses an elevated risk for people planning to stay for at least 6 months. ACIP's revision, however, targets older people in that extended-stay group.

ACIP voted unanimously to remove its earlier recommendation to consider the live-attenuated vaccine in people 65 years and older -- particularly those who have underlying medical conditions -- who will likely face at least moderate mosquito exposure in a country with no outbreak. ACIP's revised recommendations now note that being 65 years or older "is a precaution for use" of the live-attenuated vaccine in that situation.

All three votes were 14-0, with potential conflict-of-interest abstentions by ACIP member Lin Chen, MD, of Mount Auburn Hospital in Cambridge, Massachusetts.

The committee also reviewed proposed clinical guidance on chikungunya vaccine use in pregnant women and those who are breastfeeding. Although ACIP didn't vote on the measures, the draft guidance included the following recommendations:

• Pregnant women should defer vaccination until after delivery
• However, if a pregnant woman's chikungunya exposure risk is high, she should consider vaccination, given the risk of severe adverse outcomes in infants with infection
• In these cases, vaccination should happen at least 2 weeks before delivery, and it should be avoided during the first trimester
• Vaccination with the virus-like particle vaccine is preferred over the live-attenuated vaccine in pregnant women
• Immunization best-practice guidelines state that non-live vaccines such as the virus-like particle vaccine pose no risk for breastfeeding mothers or their infants

Steps to Sharpen Providers' Decision-Making Process

With two vaccine options available, some ACIP members wondered if there were enough data to make recommendations that help providers choose the best option for individual travelers. For example, if an older person were traveling to a place with no outbreak but an elevated chikungunya risk, should the virus-like particle vaccine be recommended over the live-attenuated vaccine?

Such moves may be premature, given the relative lack of strong safety data for the vaccines, explained Susan Hills, MBBS, the CDC lead on the ACIP chikungunya vaccines work group. Both vaccines were licensed through the accelerated approval process, and more definitive safety data should emerge from the vaccines' required postmarketing clinical trials and their real-world use during outbreaks.

In the case of older people traveling to higher-risk areas, "there is very clear evidence of the risk of chikungunya for this group," Hills said. "In some settings, such as if [the live-attenuated vaccine] is the only vaccine available, the benefit may fall on the side of using this vaccine -- although, with a precaution, it generally should be deferred."

Edwin Jose Asturias, MD, of the University of Colorado in Aurora and chair of the ACIP chikungunya vaccines work group, noted that "we believe that, at this point, we don't have enough data to lean toward preferential recommendation."

"There likely is going to be more evidence coming to us in the next few months, if not years, and I think this is an ongoing assessment," he said.

ACIP recommendations aren't considered final until they are published in the Morbidity and Mortality Weekly Report.

https://www.medpagetoday.com/meetingcoverage/acip/115162