Monkeypox transmission ‘occurs up to four days before symptoms appear’

The arms and torso of a patient with an active case of monkeypox (File picture)  (PA Media)
The arms and torso of a patient with an active case of monkeypox (File picture) (PA Media)

Monkeypox transmission occurs up to four days before any symptoms appear, scientists have discovered.

Analysis conducted by the UK Health Security Agency (UKHSA) estimated that over half (53 per cent) of transmission occurs in the pre-symptomatic phase, raising the possibility that infections may not be prevented by self-isolating after initial symptoms appear.

The study concluded that people would need to isolate for 16 to 23 days to detect 95 per cent of those with a possible infection.

Symptoms of monkeypox include new and unusual spots, ulcers or blisters anywhere on the body; fever; headaches; muscle aches; chills; fatigue and swollen glands.

Spread of the virus can occur when a person comes into close contact with an infected animal or an infected human. It may also occur when a person comes into close contact with material contaminated with the virus such as bedding.

As of October 31, there have been 3,552 confirmed and 149 “highly” probable monkeypox cases in the UK. Infections peaked in mid-July at around 60 per day.

London accounts for the majority of monkeypox infections, with 2,424 confirmed and highly probable cases combined. Lambeth has the highest number of cases, with 332 reported.

The new study, published in the British Medical Journal (BMJ), included 2,746 people who tested positive for monkeypox in the UK between May 6 and August 1.

People were aged 37.8 years on average and 95 per cent reported being gay, bisexual, and other men who have sex with men.

Researchers examined the time it took from when first symptoms appeared in the first patient to when symptoms developed in a second patient. They also looked at the incubation period – the time from exposure to the virus to onset of symptoms.

The findings showed that four days was the maximum time that transmission was detected before symptoms appeared.

In September, the UKHSA announced that second doses of the smallpox vaccine are being offered to those people at highest risk from monkeypox.

Commenting on the study, Dr Nachi Arunachalam, monkeypox incident director at the UK Health Security Agency, said: “Throughout this outbreak we’ve continuously reviewed and gathered data and evidence to better understand the transmission of the monkeypox virus, ensuring our response is evidence-based.

“This modelling suggests there may be some transmission of monkeypox when people are pre-symptomatic or before they recognise they have symptoms, but there is still more work needed to understand pre-symptomatic and asymptomatic infections and what that might mean for future policies and management of the monkeypox outbreak.

“Whilst we continue to see fewer cases reported in the UK, it remains vital people are alert to the risk monkeypox poses and take action to protect themselves and others.

“Vaccination plays a crucial role in this so I would encourage those at highest risk to come forward and get your first dose.”