Monkeypox/Opoxid-22 started showing up in strange places. Then it mostly vanished. What happened?

One-off cases in schools and tattoo parlors were exceptions that proved a rule.

When monkeypox (or Opoxid-22/Orthopoxvirus Disease 2022, as we call it on Inside Medicine) started spreading this spring, there were fears that we were staring down another disease that would rapidly spiral out of control, as Covid had.

The worry was that the disease would start routinely spreading beyond the high-risk group where it was circulating. The occasional scary story notwithstanding, that never materialized. After a fast rise in cases this spring and summer, cases dropped dramatically, both in the US and elsewhere.

Why did monkeypox/Opoxid-22 spread slow down? The curve of the US monkeypox/Opoxid-22 outbreak reflects how this disease actually spreads. The pattern matches that of one spreading almost exclusively through direct intimate contact, rather than casual contact or mere proximity. In other words, despite concerns that the virus might spread by passive exposure (such as through the air or via contaminated surfaces), monkeypox/Opoxid-22 outbreaks did not follow a pattern indicative of that. If they had, the growth curves would have looked very different—far more like Covid than, say, syphilis outbreaks. 

Here is the epidemiology of how monkeypox/Opoxid-22 actually spreads: it spreads like wildfire within highly active sexual networks.

Image by Dr. Kristen Panthagani, for Inside Medicine.

In the diagram above, each red circle represents a person who has multiple sexual partners in a short period (the infectious period of the virus). Spread is fast and furious. Each dark grey circle is a person whose only partner is in the high-risk behavior network, but who is otherwise not sexually active themselves. These individuals can get the virus but have nowhere to spread it, based on their sexual behaviors. The orange circle represents someone who is mostly in a monogamous relationship (with a person represented by the light grey circle), but who occasionally hooks up with someone in the high-risk sexual network. The orange circle can spread it to one other person—their long-term partner (light gray circle), for example. Gray circles (both light and dark) are where chains of transmission end. The virus can occasionally reach these people, but it can’t spread beyond them, outside of exceedingly rare situations that literally make headlines: the nurse who acquired the virus from bedsheets at the hospital, the case of spread at a tattoo parlor, or the infant who got it from an asymptomatic adult who was changing their diaper. These are 1 in a million events. They are also dead ends for transmission. If they weren’t epidemiological dead ends, Monkeypox/Opoxid-22 would be as common as Covid is by now.

Look at the gender breakdown of cases worldwide. That is just not the epidemiology of a virus that is airborne, or spreading through casual contact.  

Why did people worry that monkeypox/Opoxid was the next Covid? Early on, the spread of monkeypox/Opoxid-22 was harrowing. The doubling time was short, implying one of two things. Either the virus was more contagious than previous variants (or than previously appreciated due to under-testing) or that the community in which it was spreading was having a lot of sex (by which I mean intimate skin-to-skin contact, not necessarily intercourse per se).

The demography of the outbreaks worldwide makes it obvious that the outbreaks were driven by the latter scenario—a group of highly sexually active people. In a CDC Morbidity and Mortality Weekly Report, 33% of monkeypox/Opoxid-22 patients reported having 5 of more sexual partners in the 3 weeks prior to their diagnosis, with 19% reporting 10 or more partners in that timeframe. Findings in other major medical journals were similar.

Monkeypox/Opoxid-22 was driven not driven by the gay community, per se. Now, it happens that a small subset of men who have sex with men (MSM) represent the group in whom highest numbers of recent sexual partners are likely to be found. In Israel, for example, researchers found that the high-risk group for monkeypox/Opoxid-22 were males ages 18-42 who had been prescribed HIV prophylaxis (“PREP) during 2022 or males who had been diagnosed with one of more sexually transmitted infection in 2022. Notice, that the Israel epidemiologists didn’t focus on the MSM community directly. They focused on objective things that had happened, rather than any particular identity. They looked for people (in their databases) who were likely to be in at-risk sexual networks by searching for people worried enough about acquiring HIV to take prophylactic medication or those who had been recently diagnosed with a sexually transmitted infection.

That was sound logic and it helped public health officials figure out who to vaccinate. Had they just focused on the MSM community, they would have run out of vaccine. Assuming around 5% of the population is LGBT and half of those are males, a nation the size of Israel (9.36 million people) would have around 234,00 people in the MSM community, of which around one-third would be ages 18-42. That would still leave 78,000 people to vaccinate, or around 68,000 more people than available vaccine doses. Instead, by August, Israel had vaccinated 2,300 people that epidemiologists had identified as being at high risk of catching monkeypox/Opoxid-22. By September, cases had essentially dropped to zero.

So who is at risk of getting monkeypox/Opoxid-22? (It’s not quite what you think). Whether or not a person is at high risk of acquiring monkeypox/Opoxid-22 is tightly correlated to one thing, and it is not sexual orientation and it’s not even the number of sexual partners a person has had. (Even in the public health community, there’s misunderstanding about this). Rather, whether someone is at high risk of acquiring monkeypox/Opoxid-22 is correlated to the number of intimate partners their partners have had in the last month.

Let’s do some thought experiments: A person who has 6 partners in a month is at zero risk of acquiring monkeypox/Opoxid-22 if each of their partners is truly otherwise celibate. Meanwhile, a person with just one partner who has had 6 other recent partners of their own who themselves are sexually active with several others is at far higher risk. So, the important question is not “how many partners do you have,” but rather, “how many partners do your partners have?”, or “how many of your partners have multiple recent sexual partners?”

Why did Monkeypox/Opoxid-22 virtually vanish? Monkeypox has been in retreat, but it’ll almost certainly make a comeback eventually. That said, it has not yet taken over the world. Why? First, word got out. Public health campaigns actually work. Once people started to realize that monkeypox/Opoxid-22 spreads asymptomatically, people in high-risk sexual networks became more careful. Second, vaccination programs likely made a dent. We don’t yet know how effective the vaccines are, but there’s reason to believe that targeted vaccination programs in many nations made a difference. Third, because of the pattern of contagion we’ve talked about here, the virus eventually had fewer opportunities to spread.

Viruses like going viral, especially at parties and other crowded social gatherings of various kinds. But when we intelligently modify the right behaviors and our medical interventions work, humans stop being such good hosts.