Glasgow: The first case of monkeypox in humans was reported in 1970 in the Democratic Republic of the Congo. Since then, there have been several monkeypox outbreaks, but they have been self-limiting, ending the chain of human transmission without establishing an epidemic. However, the current outbreak is different. Human-to-human transmission is high, and it is over a very wide geographic area. in just weeks, Monkeypox has spread to 37 non-endemic countries, with over 2,600 cases. So, what are the chances of getting monkeypox in the coming weeks and months?
What we know about monkeypox varies greatly, but combining what we know with the history of other infectious diseases makes it possible to analyze possible future scenarios. The four scenarios below are based on the following knowledge: The average number of people an infected person is likely to become infected (assuming they have not been vaccinated against the virus or have had the disease before) is 2.13. It is called the original reproduction number or R. Herd immunity – the point at which enough people have immunity such that disease transmission cannot be maintained – is 53% (corresponding to this value of R). And the incubation period, the time from catching the virus to the appearance of symptoms, is between five and 21 days.
Scenario 1: Self-limiting monkeypox virus outbreak
The 2022 pandemic appears to have started as a super-spreader event that primarily involved a network of men having sex with men. But until the current outbreak, it was believed that The virus’s relatively low human-to-human transmission capacity makes the virus unlikely to spread outside early community.
In this scenario, the outbreak ends quickly after the population at risk has been immunized and herd immunity is reached at the local level. In the past, many people had some immunity (called cross-immunity) from smallpox mass vaccination programs in the late 20th century. So the effective reproduction number, R, may be close to or even less than one, and transmission will soon stop.
Behavior changes can reduce the R number even further. For example, ring vaccination can create a ‘firebreak’, reducing susceptible populations. Similar past epidemics include the SARS outbreak in 2002–04 when a quick intervention stopped the disease from spreading.
Scenario 2: All Populations
The continued spread of monkeypox in May and June 2022 suggests that the virus is moving beyond the original network.
The size of the outbreak is already well ahead of the most prominent 2017-19 outbreak in the Democratic Republic of the Congo (760). It is possible that large gatherings, including raves and festivals, have created new transmission clusters.
Scenario 2 assumes that all individuals under the age of 50 are vulnerable to infection, which marks the end of compulsory smallpox vaccination in the 1970s–80s. The virus will continue to spread, effectively finding pockets of high-risk and non-immune communities.
Unless a combination of contact tracing and ring vaccination stops the spread, monkeypox will continue to spread. But, given the low transmission potential of monkeypox, the epidemic may end before the herd immunity threshold of 50% of the population is reached.
Scenario 3: Monkeypox disease outbreak becoming endemic
Complete eradication is impossible because monkeypox is present in a wide range of animal hosts. Low transmittance also means that it can survive at low levels in the population. In addition, the long incubation period and variable symptoms allow it to evade detection. Therefore, monkeypox may have been spreading for a long time already.
In Scenario 3, after a large outbreak, the disease will settle at a long-term, relatively stable level. Similar to pre-vaccination smallpox or chickenpox.
The influx of susceptible people through birth or migration will keep the virus in the population. Mass vaccination programs may be needed to eradicate the disease. But the relatively low monkeypox transmissibility means that such programs are likely to be highly effective.
Scenario 4: Recurrent major epidemics
The current pandemic may be the first example of a series of outbreaks. In the long term (scenario 4), we should expect a return of monkeypox caused by ‘zoonotic events’ in the future, where the disease is transmitted from animal hosts to humans. As cross-immunity with smallpox vaccines decreases, the epidemic could become even more severe.
Little is known about the potential for monkeypox to mutate. Nevertheless, it is likely to evolve into a more rapidly spreading version.
Effective vaccines exist for monkeypox and are about 85% effective. Although there is currently not a sufficient dose to vaccinate everyone, there is no need for a large-scale vaccination program given the low transmission potential of monkeypox. Instead, the vaccine should be offered to those most at risk, including communities in Africa who have been exposed to wild animals carrying the virus.
(Disclaimer: The views expressed above are the personal views of Adam Klezkowski, Professor of Mathematics and Statistics, University of Strathclyde. They do not reflect those of Zee Media)