4 points to understand how worrying is the current monkeypox outbreak

The first case of monkeypox in humans was reported in 1970 in the Democratic Republic of Congo. Since then, there have been several outbreaks of monkeypox, but they have been self-limiting, ending the chain of human transmission without becoming a pandemic. However, the current outbreak is different. Human-to-human transmission is high, and has spread to many areas.

In just weeks, monkeypox has spread to 37 countries, with more than 2,600 cases worldwide. In such a scenario, the obvious question arises is how safe we are from this infectious disease. To understand this we need to delve into details of infectious diseases and some scenarios to analyse future prospects. To understand the four scenarios we need to base our knowledge on the following points.

Read | Monkeypox scare: WHO to assess if outbreak represents an international health emergency

Points on which the theories are based

1. The average number of people likely to be infected by an infected person (assuming they have not been vaccinated or had the disease before) is 2.13. This is called the original reproduction number or R.

2. Herd immunity - The point at which enough people have immunity to prevent disease transmission is 53% (corresponding to this value of R).

3. And the time from exposure to the virus to the appearance of symptoms is between five and 21 days.

Self-limiting outbreak

The 2022 monkeypox outbreak 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 assumed that the virus was unlikely to spread outside the initial community due to the virus's relatively low human-to-human transmission potential.

In this scenario, the outbreak ends quickly after the at-risk population has been immunized and locally reached herd immunity. 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.

Behavioural changes can reduce the R number even further. For example, vaccination of a population within a certain range can create a 'firebreak', which can further reduce the susceptible population. Previous similar epidemics include the SARS outbreak in 2002-04, when a quick intervention stopped the disease from spreading.

All Populations

The continued spread of monkeypox in May and June 2022 suggests that the virus is spreading beyond the original network. The is much largers than the 2017-19 outbreak in the Democratic Republic of the Congo (760). It is possible that large gatherings, including celebrations and festivals, have created favourable conditions for new transmission.

Assuming 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 tracing areas with high-risk and non-immune communities.

Unless a combination of contact tracing and ring vaccination stops the spread, monkeypox will continue to spread. However, given the low transmission potential of monkeypox, the pandemic may end before the herd immunity threshold of 50% of the population is reached.

Becoming Spatial

Complete eradication is impossible because monkeypox is present in a wide range of animal hosts. The 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 avoid detection. Therefore, monkeypox may have been spreading for a long time already.

An influx of susceptible people due to 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.

Potential for monkeypox to mutate

Recurrent major pandemics may be the first example of a series of current pandemic 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 animals to humans. As cross-immunity with smallpox vaccines decreases, the pandemic could become more severe.

Little is known about the potential for monkeypox to mutate. Nevertheless, it is likely to develop into a more rapidly spreading version.

There are effective vaccines 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, those most at risk should be vaccinated, including communities in Africa who have been exposed to wild animals with the virus.

(With Agency Inputs)