Smallpox vaccinations may not offer lifelong protection against monkeypox, research suggests, with experts saying HIV may play a role in eroding protection against the jab over time.
Outbreaks of monkeypox are ongoing around the world, with the World Health Organization declaring the disease a public health emergency of international concern. At the moment, most cases of current outbreaks are among men who have sex with men.
Vaccination with a shot originally developed to protect against smallpox, a related but more serious disease, is one of the measures taken to control infections.
While experts emphasize the importance of people at risk for monkeypox taking up a vaccination offer as it reduces the chance of symptomatic infection and serious illness, the protection offered by a smallpox shot may diminish over time. . A study of monkey pox cases in Spain found that 32 of 181 patients had previously received childhood smallpox vaccination.
dr. Oriol Mitja, co-author of the study, said that since most participants who had been vaccinated against smallpox received the shot more than 45 years ago, it is reasonable to predict that their protection would have diminished. “All I can say is that childhood vaccinations may not protect 100% for life,” he said.
Jimmy Whitworth, a professor of international public health at the London School of Hygiene & Tropical Medicine, who was not involved in the work, agreed.
He suggested there could be a number of reasons at play, including that while the viruses are similar, they are not identical, “so the cross-protection provided may not be absolute,” he said.
In addition, Whitworth noted that the study was largely based on self-reported smallpox vaccination, meaning there may have been inaccuracies.
However, Mitja said most clinicians had also checked scars and vaccination cards, or the patient had asked his mother.
Another possibility, Whitworth said, is that HIV may play a role. According to the study, 40% of monkey pox cases were in people who were HIV positive. Mitja said it was 60% of those who had smallpox vaccination in their youth but still got monkeypox. “[People with HIV] may have had some immunodeficiency, which removed the vaccine’s protection,” Whitworth said.
Laura Waters, the president of the British HIV Association, agreed. “While it is likely that the effectiveness of the smallpox vaccine will decline in everyone, it is possible that this would happen to a greater extent in people with HIV, even those with well-controlled HIV who are being treated,” she said.
Research by scientists in the US, published in 2020, found that the immune response to smallpox vaccination in children declined more quickly in people who were subsequently infected with HIV.
Prof Mark Slifka, of Oregon Health & Science University, said: “This is a potential concern that could explain why there could be more cases of monkeypox breakthrough in these current outbreaks.”
But he urged caution in interpreting the data from Spain, noting that the smallpox vaccine for children could still have provided partial immunity against monkeypox.
“We also don’t know whether the cases among previously vaccinated individuals were less severe compared to those who had not previously been vaccinated,” Slifka said, noting that another study from his team into a previous monkeypox outbreak in the US suggested that the vaccination against smallpox in children reduced the chance of getting monkeypox.
A spokesperson for the Terrence Higgins Trust said more research is needed into the vaccine’s effectiveness in people with HIV, adding that the charity is calling on the UK Health Security Agency to investigate whether people with HIV need a second dose of the vaccine. to have. Limited supplies of the vaccine mean that only one dose is currently being offered to those at risk for monkey pox.
The smallpox vaccine used in many countries, including the UK, is not the same as the vaccine given decades ago. Known as Imvanex in the UK and Jynneos in the US, the shot contains no live virus, unlike previous vaccines, making it safe for people with HIV.
dr. Carlos Maluquer de Motes, a virologist at the University of Surrey, said the current monkeypox outbreak would provide important data on the duration of immunity provided by the smallpox vaccine.
“No study has been able to measure the ‘true’ protection of [smallpox] simply because there was no disease once the smallpox was eradicated,” he said. With monkeypox closely related to smallpox, the current outbreak could provide new insights.
dr. Maluquer de Motes added: “While we believe most individuals are protected, natural variation from person to person in the efficacy of the vaccine response is to be expected and some individuals may still be susceptible to monkeypox disease. This picture will emerge as numbers increase and larger studies are conducted.