What monkeypox tells us about how well vaccines work and how vulnerable we are without them

The United Kingdom has detected seven cases of monkeypox in the last month; Portugal, five and Spain has at least eight suspected patients awaiting confirmation. Due to the international extension and the number of infections between people, these outbreaks are on the way to being the most important outside of African territory. It is not the first time that this disease, rare but present in West and Central Africa, has been exported to other countries. In fact, it is becoming more prevalent inside and outside of Africa. Why?

The first and largest outbreak of monkeypox outside of Africa occurred in 2003 in the United States.: 47 people were affected, but there was no human-to-human transmission. Those responsible—or victims, depending on how you look at it—were prairie dogs owned by an animal dealer, who had been in contact with rodents imported from Ghana infected with the virus.

Prairie dogs became infected and were sold as pets. A later study showed that those who had touched an infected animal, or received a bite or scratch, had a higher risk of infection. Cleaning the cage or the area where the animal rested also posed a higher risk.

However, the researchers found that three people had been asymptomatically infected and generated high levels of antibodies against the virus. The reason: they had received the vaccine against the eradicated smallpox 13, 29 and 38 years earlier, respectively.

The monkeypox virus belongs to the Orthopoxvirus genus, to which smallpox (Variola virus) also belongs, declared eradicated in 1980. Both are therefore very similar.

It was known that the smallpox vaccine can protect for decades. Data taken in England during an outbreak at the beginning of the 20th century showed that 93% of those over 50 years of age vaccinated in childhood avoided serious illness and death. By comparison, half of those infected at that age without vaccination died.

This protection can last a lifetime. "We found that 90% of volunteers vaccinated between 25 and 75 years ago still had humoral immunity. [de anticuerpos] and cell phone [de linfocitos T]or both, against the smallpox virus," the researchers wrote in a paper published in Natural Medicine in 2003.

For this reason, it was suspected that people vaccinated against smallpox might have some cross-immunity against monkeypox. An observational study conducted in Zaire (today the Democratic Republic of the Congo) between 1980 and 1984 had already shown that the protection was 85%.

The authors warned: "The magnitude and duration of monkeypox epidemics will increase as protection from vaccines [de la viruela] decrease in the population". Of course, the lower transmissibility would make it not persist in human populations for too long "even in the total absence of vaccination".

The prairie dog outbreak was a once-in-a-lifetime opportunity to study this in more detail. With no endemic orthopoxvirus in North America, the possibility of cross-immunity acquired by re-exposure to other viruses could be eliminated. The only population protection was the smallpox vaccine, which ceased to be used in 1972 and which 50% of the US population had received at that time.

The protection observed in the 2003 outbreak was not complete: five other vaccinated people did become infected with symptoms, compared to three who did not. The low number did not allow protection to be calculated, but it did support what was shown by previous studies: the human smallpox vaccine protects against this virus for decades, but also against similar ones such as monkeypox.

Despite all this, the original smallpox vaccines are no longer in circulation. The EMA and the FDA authorized (in 2013 and 2019, respectively) a new vaccine based on live attenuated viruses against human and monkey pox, but it is also not available to the general public. According to the CDC, experts believe that using these vaccines after exposure to monkeypox could help prevent the disease or make it less severe.

"There is very little of both right now, it would not be quick to have enough for everyone, but it would not be like starting from scratch without a vaccine," clarified the president of the Association of Foreign Health Doctors, Mar Faraco, in statements to Science Media Center.

Monkeypox was discovered in 1958 in laboratory monkeys, hence its name. In fact, it is usually transmitted by small mammals such as rats and squirrels, although apes may also play a role. The disease was first detected in humans in 1970 in the Democratic Republic of the Congo and has since been seen in 11 African countries. As usual when talking about the continent, the true burden of the disease is unknown.

In recent years, just as the researchers in the 1988 study feared, cases have increased. Nigeria has detected 558 cases and 8 deaths since 2017. The Democratic Republic of Congo has experienced hundreds of cases so far this year, with 704 reported in January and February, of which 37 died. Since January 2020, the African country has reported more than 10,000 infections and 342 deaths.

A study carried out in that country and published in 2010 concluded that cases of monkeypox had increased twenty times in 2006-2007compared to the 1980s. "Thirty years after the end of mass smallpox vaccination campaigns, the incidence of monkeypox in humans has increased dramatically in rural areas of the Democratic Republic of the Congo."

The loss of population immunity does not have to be the only factor responsible for the increase in the number of cases. "The second is the possibility that the distribution of the virus in the West African fauna has been altered in some way, increasing or broadening its spectrum, making it more likely that humans will be infected," explained the virologist at Imperial College London (United Kingdom) Michael Skinner.

There are two strains of this virus, West Africa and Congo. The lethality ranges from 1% of the mildest - that of West Africa, detected in the British cases, one of which had traveled to Nigeria - and up to 10% - that of the Congo, which is probably better transmitted. In any case, these are figures from African countries and cannot necessarily be extrapolated to places with better health services and the health status of the population.

"The risk of a major outbreak in Spain is very low," explains the president of the Association of Foreign Health Physicians, Mar Faraco, in statements to the Science Media Center. The director of the University Institute of Tropical Diseases and Public Health of the Canary Islands of the University of La Laguna, Jacob Lorenzo, agrees: "It is unlikely that monkeypox will generate significant transmission, but we must be vigilant."

Even so, the presence of numerous cases without travel history has worried health agencies around the world and suggests that, although the outbreaks can be controlled, there are more cases to appear even in other countries. Given the incubation periods, it is possible that there was invisible community transmission before the alert was raised.

"This is rare and unusual," said Susan Hopkins, UK Health Security Agency (UKSHA) chief medical adviser. "Evidence suggests there may be community transmissionspread by close contact".

Similarly, an official from the US CDC showed STAT your worry: "This is very different from what we typically associate with monkeypox. We have some concern that there may be spread outside of the UK."

To further complicate matters, all suspected and confirmed cases have been in men who have sex with men, although it is unclear whether there has been sexual or close contact transmission. So UKSHA epidemiologist Mateo Prochazka He explained that this "would have implications for the response and control of the outbreak", but warned about the importance of "addressing the discourses that reinforce inequalities and stigmas".

For all these reasons, monkeypox allows for many levels of analysis. It brings together the problem of zoonoses, emerging diseases, vaccination —or lack of it—, wildlife trafficking and the use of wild animals as pets, the stigmatization of affected population groups, the erosion of ecosystems and how health is a global problem. And, above all, it reminds us that we live on a planet full of viruses.



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