The unprecedented rise in cases of monkeypox in the UK and abroad was a waiting outbreak after the global vaccination against smallpox ended more than 40 years ago, scientists say.
The UK’s Health Security Agency announced 14 more cases in England on Tuesday, bringing the total to 70, and another patient in Scotland. No cases have been identified in Wales or Northern Ireland.
Routine vaccination against smallpox ended in most countries before 1980 when the World Health Assembly declared the disease eradicated. Because the vaccine also protects against monkeypox, the campaign has also kept the disease under control, particularly in areas of Central and West Africa where the virus is endemic.
In the decades since the smallpox vaccination ended, the proportion of people protected against monkeypox has dropped dramatically, allowing the virus to spread more easily from animals to humans and from person to person, greatly increasing the risk of outbreaks.
“This outbreak was really waiting to happen,” said Dr. Romulus Priban, a researcher at the Pasteur Institute in Paris. Mathematical modeling conducted by Priban and his team in 2020 found that in the Democratic Republic of the Congo, for example, immunity to monkeypox dropped from 85% in the early 1980s to 60% in 2012. With reduced immunity, monkeypox caused a “continually increasing threat for health security,” he wrote at the time. In 2020, the Democratic Republic of the Congo had more than 4,000 suspected cases and at least 171 deaths.
“Our level of immunity is almost zero,” Priban said. “It’s possible that people 50 or older are immune but the rest of us are not, so we are very vulnerable.” He believes the outbreak can be contained and said it was an opportunity to suggest vaccination campaigns in countries where the virus is endemic.
Until this year, only a few cases of monkeypox had been reported in the UK, all linked to travel from Nigeria. Since the UK’s first case of 2022 was announced on 7 May, nearly 300 suspected or confirmed cases have emerged in at least 16 countries.
The surge in cases has raised questions about whether the monkeypox virus has evolved into a more transmissible form. So far, scientists have found no evidence of this, but researchers are studying DNA to see if mutations in the virus have changed its behaviour. Genetic studies so far indicate that the virus matches strains that arrived in the UK, Singapore and Israel in 2018 and 2019.
Professor David Heymann, Distinguished Fellow in the Global Health Program at Chatham House, said the outbreak appears to be more than an event, with the virus amplifying once it reaches a community of MSM.
Graham Medley, professor of infectious disease modeling at the London School of Hygiene and Tropical Medicine, said it was unlikely that there would be the “explosive growth” of infection in the general population that was seen with Covid. But he said the outbreak could last for several months as contact tracing slows, but it does not stop transmission.
“As with Covid, we can expect twists and turns as the monkeypox outbreak continues,” he said. “Currently, the chains of transmission are mostly within sexually active younger men, but there are other places where there is enough contact for monkeypox to spread. The longer the outbreak lasts and the higher the rate of spread, the more likely monkeypox will find these other outlets.”
Researchers in the United Kingdom have revealed promising but tentative signs that antivirals may help reduce disease caused by the virus. In a study published in The Lancet Infectious Diseases, four out of seven patients diagnosed with monkeypox in the UK between 2018 and 2021 were given either brinkidofovir or ticofermate, drugs developed to treat smallpox.
Results from the three patients treated with brincidofovir indicate that the drug provided little clinical benefit and did not appear to reduce disease duration. However, the patient treated with tecovirimat had a shorter hospital stay and appeared to secrete the virus, which was detected by PCR tests, for a shorter period of time.
Dr Hugh Adler, co-author of the study, which took place at the University Hospitals Liverpool NHS Trust, said that although only one patient participated, the tecovirimat result was a “promising indication”.
“Now that we see more cases, unexpectedly, we think it’s important to share,” he said. “This is the sum total of human experience with these drugs and monkeypox disease so far.”
The UK has secured a supply of tecovirimat and is providing a smallpox vaccine to close contacts of people diagnosed with monkeypox to reduce the risk of developing severe symptoms and illness. Sources indicate that an additional 20,000 doses of the vaccine have been ordered to be added to the UK’s stockpile of 5,000 doses.