Vaccination of smallpox begins – Can the global epidemic be stopped?

On June 6, a person will be vaccinated at the Monkey Clinic in Montreal, Canada.Credit: Christina Muschi / Reuters

As the global incidence of smallpox increases, public health officials and researchers are questioning whether current epidemics can be contained. The World Health Organization says the situation is unlikely to turn into a full-blown pandemic. However, more than 1,000 people have been diagnosed with the virus in nearly 30 countries, where epidemics are not uncommon (see “Any Prevalence”).

Countries such as Canada, the United Kingdom and the United States have launched a so-called “ring vaccination” strategy to try to stop the spread of the virus. This involves injecting smallpox vaccines, which are thought to be effective against smallpox, into known individuals only because they are in close contact with a person who has been infected with the virus.

But there are uncertainties and challenges in using this strategy against monkeys, says Natalie Dean, a biostatrist at Emory University in Atlanta, Georgia. Although the vaccines are considered safe and effective for use in people with smallpox, the vaccines have undergone limited testing against monkeys. The strategy also relies on the search for a very strong link that may not be feasible in every country, and people must agree to be vaccinated with vaccines that are rare but have serious side effects.

Ring vaccination can be a powerful tool, says Dean, but it needs to be used sooner to be effective, and the number of cases is still manageable. “As the numbers increase and the number of contacts with each person increases, so does the logistics,” he said, adding that there is a narrow window of opportunity to prevent the virus from taking a permanent place in humans. or animal populations in countries where global epidemics are occurring.

These concerns were exacerbated on June 3 when the U.S. Centers for Disease Control and Prevention (CDC) released genomic data suggesting that there were two different strains of the monkey smallpox virus responsible for the epidemic. This finding indicates that the virus has been spreading internationally for longer than expected. But Andrea McCollum, an epidemiologist who heads the CDC’s poxvirus team, said that while new genomic data did not change the agency’s efforts to contain the virus, it did make it harder to investigate the outbreaks.

Smallpox stocks

In some countries, there are stocks of smallpox vaccines, especially public health officials, who fear that smallpox, a disease that was eradicated more than 40 years ago and kills about 30 percent of those infected, could still be accidentally spilled from laboratories where samples are stored. or may be armed. Today, there are two main types of smallpox vaccines, each containing a live smallpox virus called vaccinia, which is closely related to smallpox. Second-generation vaccines are rare, but can cause serious side effects because they contain vaccines that can replicate in human cells. Third-generation versions have fewer side effects because they contain a weakened virus that cannot be replicated.

These smallpox vaccines are considered to be approximately 85% effective against monkey smallpox infection, both according to the CDC and the WHO, citing “previous data from Africa” to support their price. But Dean warns that the figure quoted above “shakes.”

This is based on observations made in 19881 According to McCollum, in Zaire (now the Democratic Republic of the Congo), 245 people were diagnosed with smallpox and 2,278 people were in contact with them. Because second- and third-generation smallpox vaccines are relatively antibody-responsive in humans compared to obsolete first-generation vaccines used in the study, scientists believe that the new vaccines will be just as effective against monkeys. There is also compelling evidence from animal studies that they work against monkeys, but they have not been directly tested for the disease in humans, Dean says.

Contrary to how countries have responded to COVID-19, public health officials are no longer considering a mass vaccination campaign against smallpox. This is because the side effects of second-generation smallpox vaccines, which are produced by countries that are much higher than third-generation versions, prevent them from being given to children, pregnant women, people with weakened immune systems or the sick. The spectrum of skin diseases included in the classification of “eczema”. Third-generation vaccines have access to fewer countries, they have fewer side effects and can therefore be given to more people.

At present, the risk of monkey disease to the general public, given the adverse effects and access issues, is not sufficient to require mass vaccination, says Daniel Baush, director of emerging threats and global health security at the Innovation New Foundation. Diagnostics in Geneva, Switzerland. However, if the virus begins to spread in vulnerable populations, such as pregnant women or children, or if the death rate is higher than expected, this risk-benefit calculation may change.

To date, no monkey deaths have been reported outside Africa; but in 2022, 4.7% of people infected with monkey disease died in seven countries in West and Central Africa. This is a ring in non-African countries, or more broadly – a discussion of the vaccination campaign for African researchers who have been battling monkeys for decades, said Ifedayo Adetifa, head of the Nigerian Center for Disease Control in Abuja. WHO member states have promised the agency more than 31 million doses of smallpox vaccine for use in emergencies, but these doses have never been used against monkeys in Africa.

limited date

Leprosy often causes fever, swollen lymph nodes, and sometimes painful fluid-filled sores on the skin. If left untreated, the infection can clear up in a few weeks – especially for people who have access to medical care.

Bavarian Nordic, a biotechnology firm based in Hellerup, Denmark, which developed the third-generation MVA-BN vaccine against smallpox, said on May 30 that it was taking orders in response to global demand. Raina McIntyre, an epidemiologist at the University of New South Wales in Sydney, Australia, says it would be “unwise” to use third-generation smallpox vaccines if countries had more stocks. The monkey smallpox vaccination campaign.

So far, the United States has recommended a second- or third-generation smallpox vaccine regimen for people at “high” or “medium” risk, which the CDC defines as “unprotected skin contact.” The monkey was at a distance of 6 feet (1.8 meters) from the body fluids of an infected person or an infected person. According to the CDC, smallpox vaccines are believed to protect against monkey smallpox infection if given within four days of illness.

However, there is limited real-world data to support this guidance. Although the second-generation vaccine accumulated in the United States is to be administered as a single dose, MVA-BN is a two-dose vaccine administered at 28-day intervals. It is unclear whether a single dose of MVA-BN will be enough to stop the infection due to the lack of testing for smallpox in humans, McCollum said.

Challenges ahead

Although many countries are looking for smallpox vaccines and launching a ring vaccination campaign, McIntyre warns that there is a big difference between theory and reality when it comes to implementing a strategy. Theoretically, smallpox is more suitable for ring vaccination because it spreads more slowly than most human viruses and has a longer incubation period. But in reality, a successful ring vaccination campaign relies on strong testing and contact retrieval infrastructure, as well as the ability to quickly vaccinate against any dangerous contacts, he says.

And it can be difficult for people to get vaccinated. According to the report, as of May 24, only 15 of the 107 people in public contact in the UK and 169 of the 245 health workers had decided to receive the MVA-BN vaccine after contracting smallpox during the current epidemic. Eurosurveillancetwo.

To avoid tensions and misinformation, health workers need to make it clear to the public why the campaign is needed and why only selected people are getting vaccines, said Bausch, who has worked with the WHO and the British government to tackle the Ebola epidemic. Another concern is the stigma surrounding the modern monkey smallpox epidemic: it has often occurred in men who have sex with men. According to Baush, if the disease continues to be stigmatized, people may be reluctant to submit to contact-seeking efforts, which makes ring vaccination more difficult.

To stop the spread of the virus, health workers need to look beyond quarantine and focus on quarantine and isolation, as well as community education, he added. Baush wrote in a comment in 2021 Nature Medicine3Despite the success of the ring vaccination, “it’s far from a panacea”.

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