As global cases of monkeypox continue to rise, public health officials and researchers wonder if the current outbreaks can be contained. The World Health Organization has said the situation is unlikely to escalate into a full pandemic. But more than 1,000 people have now been confirmed to have been infected with the virus in nearly 30 countries where outbreaks don’t usually occur (see ‘Unusual spread’).
Countries like Canada, the United Kingdom and the United States have started implementing a strategy called “ring vaccination” to try to stop the spread of the virus. This involves giving smallpox vaccines – which are believed to be effective against monkeypox because the viruses are related – to people who are known to have been exposed through close contact with an infected person.
But there are unknowns and challenges that come with using this strategy for monkeypox, says Natalie Dean, a biostatistician at Emory University in Atlanta, Georgia. Although the vaccines are considered safe and effective for use in people infected with smallpox, the vaccines have had limited testing against monkeypox. The strategy also relies on very rigorous contact tracing, which may not be implemented in all countries, and people must also agree to be inoculated with vaccines that can lead to rare, but serious side effects.
Ring vaccination can be a powerful tool, Dean says, but to be effective it needs to be used early – while case numbers are still manageable. “As the numbers go up and you think about the number of contacts each individual has, the logistics get more and more complicated,” she says, adding that there is a window of opportunity opening up. shrinks to prevent the virus from taking hold more permanently in humans. or animal populations in countries where global epidemics occur.
These concerns were further heightened on June 3, when the US Centers for Disease Control and Prevention (CDC) reported genomic data showing that there are two distinct strains of the monkeypox virus responsible for the outbreaks. This discovery could suggest that the virus has been circulating internationally for longer than expected. But Andrea McCollum, an epidemiologist who leads the poxvirus team at the CDC, says if the new genomic data doesn’t change the agency’s efforts to contain the virus, it will complicate investigating the origins of the outbreaks.
Some countries keep stocks of smallpox vaccines, mainly because public health officials fear that smallpox – a disease eradicated more than 40 years ago that can kill around 30% of infected people – is yet to be accidentally released. laboratories where the samples are kept, or could be armed. Two main types of smallpox vaccines are available today, each containing a live poxvirus, called vaccinia, which is closely related to smallpox. So-called second-generation vaccines can cause rare but serious side effects because they contain a vaccine that can replicate in a person’s cells. Third-generation versions have fewer side effects because they contain a weakened virus that cannot replicate.
These smallpox vaccines are thought to be about 85% effective against monkeypox infection, according to the CDC and WHO, which both cite “past data from Africa,” where outbreaks have occurred. produced for decades, to support their assessments. But the much-quoted number is “fragile,” warns Dean.
It comes from a 1988 observational study1 conducted in Zaire (now the Democratic Republic of the Congo) that studied 245 people infected with monkeypox and 2,278 of their contacts, according to McCollum. Because the second- and third-generation smallpox vaccines produce a comparable antibody response in humans to the now-outdated first-generation vaccines administered in the study, scientists believe the new vaccines would have similar efficacy against smallpox. of the monkey. There is also compelling evidence from animal studies that they may work against monkeypox, but they have not been directly tested against this disease in humans, Dean says.
Unlike how countries have responded to COVID-19, public health officials are not currently considering a mass vaccination campaign against monkeypox. This is because the side effects of second-generation smallpox vaccines, which have been stockpiled by countries at a much higher level than third-generation versions, make it impossible to give them to children, pregnant people, immunocompromised people or to a range of skin conditions that fall under the classification of ‘eczema’. Third-generation vaccines, which fewer countries have access to, have fewer side effects and could therefore be given to a greater proportion of people.
At this time, the risk posed by monkeypox to the general public is not high enough to warrant mass vaccination, given the side effects and availability issues, says Daniel Bausch, director of emerging threats and Global Health Security at the Foundation for Innovative New Diagnostics in Geneva, Switzerland. But if the virus begins to spread in vulnerable populations such as pregnant women or children, or if it turns out to have a higher than expected death rate, this risk-benefit calculation could change.
No deaths from monkeypox have been reported outside of Africa so far this year; however, 4.7% of people who contracted monkeypox in seven West and Central African countries in 2022 died. This makes the discussion of a ring vaccination campaign – or even wider – in non-African countries for African researchers who have been fighting monkeypox epidemics for decades, says Ifedayo Adetifa, director of the Nigeria Center for Disease Control in Abuja . WHO member countries have pledged more than 31 million doses of smallpox vaccine to the agency for use in smallpox emergencies, but those doses have never been used against monkeypox in Africa.
Usually, monkeypox causes fever, swollen lymph nodes, and sometimes painful fluid-filled lesions that form on a person’s skin. Without treatment, the infection can clear up within weeks, especially for those who have access to healthcare.
Bavarian Nordic, a biotech company based in Hellerup, Denmark, which created the third-generation smallpox vaccine MVA-BN, said May 30 that it was taking orders in response to global demand. If countries had a larger stockpile of third-generation smallpox vaccines, Raina MacIntyre, an infectious disease epidemiologist at the University of New South Wales in Sydney, Australia, says it would be “insane to use them for a robust monkeypox vaccination campaign.
So far, the United States has offered a second- or third-generation smallpox vaccination regimen for people at “high” or “intermediate” risk of exposure, which the CDC defines as someone who has had “unprotected contact” with the skin or bodily fluids of someone with monkeypox or who was within 6 feet (1.8 meters) of an infected person. Smallpox vaccines are thought to protect against monkeypox infection if given within four days of exposure, according to the CDC.
But there is little real data to back up these directions. Although the second-generation vaccine stocked in the United States is intended to be given as a single dose, MVA-BN is a two-dose vaccine, given with 28 days between injections. Due to the lack of testing for monkeypox in humans, it’s unclear if a single dose of MVA-BN would be enough to stop an infection, even if given within four days of exposure, says McCollum.
Even if more countries buy smallpox vaccines and launch a ring vaccination campaign, there’s a big difference between theory and reality when it comes to implementing the strategy, MacIntyre warns. In theory, monkeypox is conducive to a ring vaccination approach because it spreads slowly compared to most human viruses and has a long incubation period. But in reality, a successful ring vaccination campaign relies on a robust testing and contact tracing infrastructure, as well as the ability to vaccinate all high-risk contacts quickly, she says.
And getting people to get vaccinated could be difficult. As of May 24, only 15 of 107 community contacts and 169 of 245 healthcare workers in the UK have elected to take an MVA-BN vaccine after possible exposure to monkeypox during current outbreaks, according to a report published in Eurosurveillance2.
To avoid tension and misinformation, health officials will need to communicate very clearly to the public why the campaign is needed and why only certain people are getting vaccines, says Bausch, who has worked for the WHO and the UK government to cope. to Ebola outbreaks. Another concern is the stigma building up around the current outbreaks of monkeypox: many cases involve men who have sex with men. Bausch says if the disease continues to be stigmatized, people might not want to comply with contact tracing efforts, which would make ring vaccination much more difficult.
To stop the spread of the virus, health officials will likely need to look beyond vaccination and focus on quarantine and isolation, as well as community education, he adds. As Bausch wrote in a 2021 comment in natural medicine3although ring vaccination has had its successes, “it is far from being a panacea”.
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