Commentary: Four ways the monkeypox outbreak can develop

In this scenario, the outbreak ends quickly once the population at risk becomes immune and herd immunity is reached locally. In the past, many people had some immunity (called cross-immunity) thanks to the mass smallpox vaccination programs of the late 20th century.

So the effective reproduction number, R, can be close to or even less than one, and the transmission will soon stop.

Behavioral changes can further reduce the R number. For example, ring vaccination can form a “firewall”, further reducing the susceptible population.

Similar previous epidemics include the SARS outbreak from 2002 to 2004, when rapid intervention stopped the spread of the disease.

SCENARIO TWO: THE VIRUS SPREADS AND THEN SLOWS OFF

The continued spread of monkeypox in May and June suggests that the virus is moving beyond the original network.

The size of the outbreak already far exceeds the most prominent outbreak from 2017 to 2019 in the Democratic Republic of the Congo (760 cases). Large gatherings, including raves and festivals, may have created new streaming groups.

This scenario assumes that everyone under the age of 50 is susceptible to infection, reflecting the end of mandatory smallpox vaccination in the 1970s and 1980s. The virus will continue to spread, effectively seeking out pockets of non-immune communities and high risk.

Unless a combination of contact tracing and ring vaccination stops the spread, monkeypox will continue to spread. But, given the low transmissibility of monkeypox, the epidemic may die out before reaching the herd immunity threshold of 50 percent of the population.

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