Potential for Mpox Resurgence This Summer: Q&A With CDC's Christopher Braden, MD

Christopher Braden, MD


May 18, 2023

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Although mpox cases in the US have plummeted since a peak in early August 2022, the virus is still circulating. The Chicago Department of Health reported 12 confirmed cases and one probable case from April 17 to May 5. With the return of summer festivals, public health experts are renewing calls for vaccination and prevention efforts. Medscape Medical News spoke with Christopher Braden, MD, deputy director of the National Center for Emerging and Zoonotic Infectious Diseases at the Centers for Disease Control and Prevention (CDC), to prepare the clinician community.

How big of a problem is mpox currently?

There's been quite a decrease in the number of cases since the height of the outbreak — when we were seeing upwards of 450 cases a day, totaling over 30,000 cases. What we're seeing now is a very long tail of a few cases being reported across the country. We're seeing cases reported from jurisdictions that have seen large numbers of cases in the past. That means the outbreak is not over.

We're likely going to see more cases associated with that cluster in Chicago, so that may be a harbinger of things to come in other places. What's concerning is that in Chicago, many cases are among vaccinated persons. We're going to investigate with the Chicago and Illinois Departments of Public Health about what's going on there.

With some mpox cases occurring in people who were vaccinated, has the CDC changed their vaccine recommendations?

Top of mind is whether our estimate of vaccine effectiveness is wrong in any way. Are we estimating it to be too high? [Editor's note: Full vaccination with JYNNEOS is estimated to be 69% effective at preventing mpox disease, according to the most recent published data.] But we have several upcoming publications that indicate that the vaccine effectiveness is like what we've estimated previously.

The second thing that we are concerned about is if the immunity induced by the vaccine could be waning over time, like we saw with COVID vaccines. We have ongoing studies looking at this very question, in places that have seen mpox for a very long time, like the Democratic Republic of Congo, but also in the US in communities like Washington, DC, and Los Angeles. So far, we don't think we need to change our vaccination recommendations.

How concerned are experts about a resurgence of mpox cases this summer?

We know there are low levels of circulating virus around the country, and in many of those places, vaccine coverage is quite low — low enough to where they're still at risk for seeing outbreaks, and potentially large outbreaks, in the future. It's great that we've been able to vaccinate over 1.2 million people at high risk in this country, but that is a minority of the population at risk. If you take that population at risk as a whole in this country, that's probably about 23% coverage for full vaccination. It might be a bit larger than that when considering those who received just one dose of JYNNEOS, but we really recommend that people take both doses for as much protection as can be achieved.

We've done some modeling of future outbreaks if we have low vaccine coverage — like 15% — in some locations vs the risk of outbreaks occurring in other jurisdictions that have had quite high vaccination coverage, like for instance, in Washington, DC. So, the risk differs by jurisdiction based upon their vaccination coverage. For jurisdictions with more than 75% vaccination coverage, the risk for a new outbreak is estimated to be between 5% and 12% each year over the next 5 years if mpox is reintroduced. In areas with low vaccine coverage (under 35%), recurrent outbreaks are more likely.

Who should clinicians be most concerned about being vulnerable to mpox infection?

By far, the population with the highest infection rate in this country is gay and bisexual men and other men who have sex with men. We have seen a small number of cases in cisgender women or young children, but those exposures tend to be household exposures — where you're living with somebody else who has the infection. Transgender, nonbinary, or gender diverse people who have had more than one sex partner or a sexually transmitted infection (STI) in the past 6 months also have a higher risk of acquiring mpox. Anyone who has had sex in a commercial sex venue, sex related to large commercial events, or sex in exchange for money or other items in the past 6 months, we also consider to be at risk. Then importantly, people with uncontrolled HIV or other immune suppressing conditions are at higher risk for severe mpox disease or even death. We have focused our recommendations on these groups of people and targeted them for vaccination.

Who else is eligible for the vaccine?

It's recommended that people who have had exposure to the mpox virus or are at high risk of having had exposure to the virus receive postexposure prophylaxis via the mpox vaccine. This includes people who had a sex partner in the previous 2 weeks who was diagnosed with mpox. It's best to get that vaccine in the first 4 days after exposure, but even vaccination up to 14 days after an exposure may provide some benefit.

What signs and symptoms should clinicians look to diagnose mpox cases?

Clinicians should really consider mpox when they're considering other infections in the same differential diagnosis. Those other infections include herpes simplex virus, syphilis, herpes zoster, disseminated varicella zoster virus infection, molluscum contagiosum, scabies, lymphogranuloma venereum, allergic skin rashes, and other drug eruptions. Fever and lymphadenopathy could also indicate infection, and people with infection of the mucosa can also experience oral pharyngeal pain or rectal pain.

As a part of the patient workup, clinicians should conduct a thorough history of sexual exposure. Mpox is transmitted through close sustained physical contact and has almost exclusively been associated with sexual contact in these outbreaks. The physical exam should include a thorough skin and mucosal examination of oral, genital, and anal areas for the characteristic pustular-vesicular rash of mpox. This lets clinicians detect those lesions that patients may not even be aware of.

What can clinicians tell their patients about mpox prevention, including vaccination?

They should really be urging their patients to be vigilant about mpox, especially with spring and summer festivals coming up. Individuals also may need to temporarily alter their sexual behavior in some ways to prevent being exposed and infected with mpox.

People who are at risk should be offered and encouraged to take the vaccine. It can be given intradermally, and it doesn't have to be just on an arm. It can be given on the back and so on, if people don't want that intradermal injection to be noticed. It also can be given subcutaneously. People need two doses for the best protection against mpox, and it takes 2 weeks after the second dose for the vaccine to be fully effective. So, people need to plan their prevention activities, especially around the festival season.

Last summer, there were issues with supply of the vaccine. Has that issue been resolved?

We have plenty of supply to be able to ship to the jurisdictions who request the vaccine. We would love to see an uptick in the number of people being vaccinated.

Are there additional data on vaccine effectiveness since December 2022?

We have three publications coming out to the MMWR and one in The New England Journal of Medicine that look at vaccine effectiveness in different ways. We can say that the point estimates may vary by study, but they all fit within the range that we've already established for vaccine effectiveness. That's good news: Vaccine effectiveness is substantial, and it's holding up with further study. We've also looked at intradermal vs subcutaneous vaccine effectiveness, and both methods appear to be equally effective, although there are smaller numbers of patients in those analyses.

I don't want this observation that we've seen a number of cases among vaccinated people to somehow dampen the enthusiasm to get the vaccine. We know that it can limit transmission, but it's not 100%. When we look at the vaccine effectiveness, it is 69% as our point estimate. But in addition to preventing transmission, the vaccine can decrease the severity of illness, risk for hospitalization, and even death among those who are quite immunocompromised.

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