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Remember monkeypox? It may be back in headlines
Remember monkeypox? Well, it’s now known as “mpox.” And you may start seeing it pop up in the news again. We have learned a lot since the massive outbreak last summer, but still have a lot of unanswered questions.
Here’s what you need to know, particularly going into Pride month.
What’s going on?
Last summer’s U.S. outbreak largely concluded by winter, resulting in a beautiful bell-shaped curve below. We would get a few cases a week, but nothing explosive. Containment was largely attributed to grassroots organizations: engagement, testing, and vaccination.
However, last month the CDC identified a new cluster of mpox cases in Chicago. CDC has also reported remnants of mpox in wastewater, without linked cases, meaning it’s likely spreading undetected. The Western Pacific has an uptick in cases, and the U.K. just reported an outbreak of 10 new cases in London, too.
Combine this with changes in behavior during Pride month, and we may be on the cusp of an outbreak. The CDC thinks the likelihood of this happening is “substantial.”
Who is at risk?
Mpox is a super stable virus, which means it can last on surfaces for a very long time and can be airborne. But, what’s possible isn’t always probable. Mpox’s main route of transmission remains to be prolonged, very close contact, like sex.
Mpox continues to spread through one very tight social network: men who have sex with men. Yes, some straight men got it, as well as women and children, but at relatively low rates. (Of all the cases worldwide, 1% were children and 3% were women, and they were mainly household close contacts.)
This means that if you are not in this tight network, there is very, very low risk for you.
Is it an STD?
Mpox is certainly among diseases that we know are sexually transmitted. Last summer we didn’t know if there was active virus in semen. It turns out that there is, but lab data show lesions or open sores are most contagious. It’s almost impossible to discern whether people in the “real world” are infected from lesions or semen given that sex is close contact.
We don’t know about asymptomatic transmission.
Mpox can be spread 4 days before symptoms start (i.e. pre-symptomatic transmission), but the probability of being contagious with no symptoms at all is unknown.
Death is very rare.
Last summer we relied on historical data in Africa that showed mpox had a 1-10% fatality rate. But we didn’t know whether the high mortality rate was partially attributed to low access to care and limited resources in Africa. Could it be lower with better access to care?
The answer is yes. There have been over 87,000 cases worldwide but only 143 deaths. This equated to a 0.16% case fatality rate. The majority of deaths were among immunocompromised people, particularly those with uncontrolled HIV disease.
The virus didn’t mutate.
Mpox took the world by surprise, particularly given the way it spread and the sheer size of the outbreak. One key question we had: Did mpox mutate to become more like smallpox?
Thankfully, it did not. The genetic makeup of the virus last summer didn’t look much different than in previous outbreaks. This was one clue that the outbreak is likely being driven by environmental conditions. We are still trying to understand why now, and why in this population.
Vaccines are working.
We have an mpox vaccine, called Jynneos, but last summer we didn’t know how well it worked. Recent data shows that it works really well: 68-88% effective against severe disease. It works particularly well after the second dose.
There’s a lot we still don’t know, though:
How long does protection last?
Does it stop transmission?
What is the impact on viral load?
Why are we seeing breakthrough cases?
Just like with COVID-19 or other vaccines, these vaccines are not perfect. The FDA and CDC are studying antibody data, but no word on boosters yet.
Unfortunately, only 28% of eligible people are fully vaccinated, which isn’t enough to help prevent a future outbreak on a population level. (Wondering if you’re eligible? Check out the recommendation here.)
Intradermal injections are working, too.
Last summer we didn’t have enough vaccines to meet demand, so we started vaccinating intradermally which takes ⅕ less the vaccine formula than injections. We now know that this route works just as well as an injection.
Antivirals are working, but…
The antiviral for mpox (TTPOX) is also working well for those at high risk, particularly immunocompromised. However, a new preprint reports that it’s causing drug resistance. This means that if these outbreaks continue, we are going to need updated treatments.
What about Africa?
The above story is consistent in almost all places except Africa, where mpox has remained endemic for decades. It remains a poorly resourced health threat there, too, which means we don’t really understand the viral details: How many times is it jumping from animals to humans? How well is it spreading?
In Africa, there are two types of mpox: Clade I (which is more severe but mainly transmitted from animals to humans through hunting) and Clade II (which is less severe but spreading worldwide). One big concern is Clade I could start spreading more efficiently from human to human.
We don’t know mpox’s future. Will it become endemic everywhere with sporadic outbreaks (like we are seeing in the U.S.), or will it eventually fade with time and remain at low levels in Africa? Elimination, altogether, is unlikely unless support, like surveillance, control measures, and research, is maintained and strengthened worldwide.
1.6 million people are at risk for mpox in the U.S.; for everyone else, there is no need to worry. If you’re high risk, now is the time to protect yourself. As one epidemiologist famously says: Our best defense is a good offense.
P.S. A huge thank you to Dr. Anne Rimoin, a leading mpox expert at UCLA, for fact-checking this post late at night after teaching classes!
“Your Local Epidemiologist (YLE)” is written by Dr. Katelyn Jetelina, MPH PhD—an epidemiologist, data scientist, wife, and mom of two little girls. During the day she works at a nonpartisan health policy think tank and is a senior scientific consultant to a number of organizations, including the CDC. At night she writes this newsletter. Her main goal is to “translate” the ever-evolving public health science so that people will be well-equipped to make evidence-based decisions. This newsletter is free thanks to the generous support of fellow YLE community members. To support this effort, subscribe below: