Effective monkey pox screening may reduce vaccine need

The conclusions are from a pre-print study – that is, which has not yet been reviewed by other scientists – that sought to identify the effects of the three measures in the community that most registers cases of the disease, men who have sex with other men ( MSM).

The researchers used the infection’s effective reproduction number (Rt). This value indicates how the disease is spreading. If the Rt is equal to 1, this indicates that each infected person transmits the disease to one more person. Ideally, the number should be below 1 because it is an indicator of less spread of the infection.

Based on the current scenario of monkeypox in the United States, the authors considered the Rt in the community of men who have sex with men to be between 1.2 and 2.0. That is, an infected person transmits the disease to at least one other person, with up to two new infected people for each patient.

Then, the approximate effect that each of the measures would have on reducing the transmission of the disease in the US was observed. For example, the researchers found that the detection of a case can reduce the appearance of new diagnoses by 50%. If this detection is early, the reduction would be 90%.

The researchers estimated the impacts of actions to stop the transmission of the disease in different scenarios.

One such scenario was with an infection reproduction number of up to 1.4. In this case, detecting 40% of cases and tracing half of the contacts of these patients could result in a reduction in the reproduction number to below 1. Vaccination, in this scenario, would not be an adopted measure.

Another example considered in the study is with a poor model of testing and tracing, in which only 10% of cases would be detected and there would be no tracing of contacts. Situations like these would require a high amount of vaccines to reduce the transmission of the disease. In a context where each infected person transmits to two more people, immunizations would be needed for almost half of men who have sex with men in order to reduce the Rt to below 1.

A third scenario observed was a moderate response regarding testing and tracing – 20% of cases would be detected and 25% of contacts would be under observation. Dependence on immunizers would be lower, but would still exist. In a context of high spread – with each patient transmitting to two people –, 45% of men who have sexual contact with other men would need to be immunized to stop the spread of the virus.

Andrea von Zuben, professor of epidemiology at the postgraduate program in public health, policies and health management at the Faculty of Medical Sciences at Unicamp (State University of Campinas), says that the study includes the main actions involved in controlling a disease infectious. However, a mathematical estimate will not necessarily be replicated in the daily life of the population.

According to her, high testing capacity and contact tracing are measures that can considerably reduce smallpox transmission from monkeys. The problem is that many cases of the disease have subtle symptoms, which makes diagnosis and isolation difficult.

“When we look at the mathematical model, it’s perfect. Now, as the disease can go unnoticed, the person may not know they’re infected. That’s the challenge right now.”

Another problem is Brazil’s testing capacity. Currently, the country has four laboratories that centralize diagnoses. With the increase in cases in the country, the centers already indicate overload at work.

For Von Zuben, carrying out tests as quickly as possible is essential for patient isolation. “If we know that the isolation of the patient is very important, he knows if he has the disease makes a lot of difference”, she says.

In contexts where there are difficulties in detecting cases and tracing their contacts, the use of vaccines in key groups is important to prevent new diagnoses. “The vaccine is much more effective in this blockade [de novas infecções] because it does not depend exactly on the self-awareness of each one [em optar pelo isolamento].”

So far, the Ministry of Health has announced the order of 50,000 doses of the immunizer. They should be applied to health professionals and people who have had contact with patients.