How well does the monkeypox vax work? Nobody knows for sure

In an American gay men’s community worried about catching monkeypox, news suggests this is all temporary: A few months of sexual caution plus vaccination will herald a worry-free fall.

“For your own safety and to spare you the horrors of this disease,” said sex columnist Dan Savage suggested on Twitter Last weekend: “You might want to consider recalling it maybe for a couple of weeks while we roll out the vaccine.” The AIDS Magazine POZ advises readers to “wait and see for a messy summer” and wait for the fall, when “we hope to have enough Jynneos vaccines for everyone who wants it”.

Yet nobody knows how well the Jynneos vaccine will serve as an infection-free map.

A number that has undoubtedly been quoted by various media organizations – “85% effective” or “at least 85% effective” – ​​is based solely on a small study conducted in Africa in the 1980s and has major limitations. A data expert calls his results “pretty weak”. Other studies have only been done on animals.

Still, “I’ve heard from a lot of people in the community that they expect almost no risk of infection two weeks after their first injection,” she said Michael Donnelly, MSc, a New York data scientist and LGBT health advocate, in an interview with MedPage today. “Or they think they won’t get any symptoms if they were exposed before their needle.”

The lack of accurate information about the vaccine is “a major concern,” said Jay Varma, MD, director of the Cornell Center for Pandemic Prevention and Response in New York, in an interview. “It is absolutely critical that public health officials work to pass this uncertainty on to those who need to be vaccinated.”

Vaccine assumptions based on a small, “weak” study from 1988

As of July 29, the CDC reports that the current outbreak has caused 5,189 infections in the United States, hitting almost every state (all except Montana, Wyoming, and Vermont) plus Puerto Rico. New York is by far the hardest-hit with 1,345 cases, followed by California with 799, Illinois with 419, Florida with 373, and Texas and Georgia with 351 each. Washington DC has a particularly high number with 218 cases in a city of 702,000 per capita rate.

Men who have sex with men are thought to be the most vulnerable – accounting for 98% of 528 cases worldwide, according to a recent analysis – and many gay men have taken to social media or spoken to reporters about severe pain, horrific lesions and to describe barriers care.

Hundreds of thousands of Jynneos smallpox/monkeypox vaccines are now available in the US, and the CDC recommends vaccination for those who have been exposed to, or are at higher risk of, monkeypox.

Health officials prefer the Jynneos vaccine, made by Danish company Bavarian Nordic and approved by the FDA, to prevent both smallpox and monkeypox. An alternative vaccine, ACAM2000, is complicated to administer, produces an uncomfortable and infectious pustule, and may affect some people, e.g. B. in people with a weakened immune system, cause side effects vox

As the CDC notes, “no data is yet available on the effectiveness of these vaccines in the current outbreak.” As with previous outbreaks, only one study — a retrospective analysis published in 1988 — has examined whether a smallpox vaccine could prevent monkeypox.

In this study, researchers traced the household contacts of 209 people infected with monkeypox in Zaire in the early 1980s. Those with scars from previous smallpox vaccinations (70%) were 85% less likely to be infected. The vaccine appeared to be 89% effective at protecting contacts outside the home from infection.

Statistical analysis is limited because it doesn’t have a confidence interval or adjustment for factors like age, said Ira Longini, PhD, a biostatistician at the University of Florida MedPage today. Also, he said, the data is based solely on physical signs of vaccination. The study “is the only shred of evidence we have [in regard to vaccine effectiveness], which is pretty weak. In principle it should work, but we don’t know.”

Jynneos and ACAM2000 are newer generations of vaccines like Dryvax that were used in the 1980s. “These vaccines have not been tested directly against smallpox or monkeypox,” said Dr. Richard Kennedy, co-director of the Mayo Vaccine Research Group in Rochester, Minnesota, in an interview MedPage today. “The immune responses they elicit are very similar to those of first- or second-generation vaccines: a little weaker, but not by much.”

Kennedy added that the vaccines were also tested against monkeypox in five to 10 different animal studies. “These data are also clear and consistent with very good protection from disease, with animals showing very little or no disease symptoms post-challenge,” Kennedy said. “The animal data were strong enough that the FDA approved Jynneos for the prevention of monkeypox.”

A unique outbreak can weaken the effectiveness of the vaccine

To complicate matters further, the new outbreak is very different from the past. This time around, the virus appears to be transmitted primarily through sexual rather than other types of contact, with an overwhelming majority of cases occurring in men who have sex with men. (There is now a debate in the medical world about whether to call monkeypox a sexually transmitted disease [STD].) Previous outbreaks in Africa appeared to have been spread through households in a variety of ways.

“The vaccine was evaluated under the assumption that most or all exposures would be through skin-to-skin contact,” Varma said MedPage today. “The head of the penis and the inside of the anus can have characteristics that make them more susceptible to infection, such as: B. a lower dose of virus needed, less antibodies or other components of the immune system or concomitant sexually transmitted diseases that increase the risk. It’s possible. The level of protection may be the same, but we shouldn’t assume it’s the same without evaluating it.”

He also said: “It is theoretically possible for a monkeypox virus to develop mutations that make it more contagious or virulent to humans. The scientific consensus is that this is less likely to happen as quickly as with COVID, given the nature of the virus. COVID is an RNA virus and monkeypox is a DNA virus.”

Kennedy agreed. “The current outbreak is caused by a strain that has some genetic differences but is still very similar to the strains that caused monkeypox in the 1980s,” he said. “It’s not like COVID-19 where you have a new strain with significant immune evasion every few months. There is a lot of cross-protection with smallpoxviruses – an immune response to one smallpoxvirus can recognize most other smallpoxviruses.”

Fine-tuning a monkeypox prevention message

Despite the weak evidence, the 85 percent effectiveness can be found everywhere – sometimes with limitations, sometimes not. Even Yale University and Harvard University have issued health warnings citing the figure of 85% without mentioning its uncertainty.

Meanwhile, monkeypox prevention messages aimed at gay and bisexual men continue to vary. Vaccinations are being heavily touted along with other strategies as officials worry about stigma against gay men.

Last week, the head of the World Health Organization suggested “reducing the number of sexual partners, reconsidering sex with new partners, and sharing contact details with all new partners to enable follow-up if necessary.”

The CDC gave advice about sex when someone might be infected: Stay 6 feet apart during mutual masturbation and avoid kissing. And the magazine POZ suggests using condoms, wearing more clothes to circuit parties and bars, and creating sex “pods” similar to the groups of friends and relatives who only came into contact with each other during the COVID-19 pandemic.

Suggestions about condoms can be particularly difficult for men who have sex with men to accept. Many gay men prefer to reduce their risk of HIV transmission by taking preventive medications such as emtricitabine/tenofovir (Descovy, Truvada) or, if they are HIV positive, by taking medication to lower their viral load to undetectable levels.

“The prevention message should be that vaccination will be an essential part of controlling this outbreak and we need to get everyone vaccinated as soon as possible,” said Donnelly, a data scientist and LGBT public health advocate. “But even if you’re vaccinated, you’re still at risk, and unprotected anal sex can be the highest risk.”

“Even after vaccination,” he added, “you may want to consider reducing the number of your sex partners and using condoms or other safer sex approaches.”