Attorney Robert F. Kennedy Jr. and his US followers over the last 25 years have staunchly opposed vaccines, latching on to any claim that they cause autism or should be available for lawsuits even if they harm no one.

They really won’t like a new experimental vaccine for Smallpox and Monkeypox that avoids the side effects of a current live virus version while not needing two doses, as the replication-deficient virus version does. It uses the horsepox virus as a protective agent to confer the safety of a multi-dose vaccine in a single shot. 

Smallpox, caused by the variola virus beginning thousands of years ago, is highly contagious disease with a fatality rate between 30% and 97%, 300,000,000 in the 20th century alone. Though the World Health Organization (WHO) said it could never be eradicated, the US government took it upon themselves and was so successful that in 1980 WHO conceded American scientists were right. 

(L) Dr. D.A. Henderson and (R) Dr. Bill Foege saved hundreds of millions of lives using a surveillance–containment strategy for smallpox that the UN said was flawed.

The article claims the experimental vaccine is substantially more attenuated than the vaccinia virus used in the single-dose vaccine already approved by the U.S. Food and Drug Administration. 

Monkeypox (mpox) is caused by the monkeypox virus, similar to variola in that it is a member of the genus Orthopoxvirus but with a much lower fatality rate, Because of their similarity the two FDA-approved vaccines for smallpox are also use to prevent mpox. To get a single-dose version without risk of side effects, scientists used a virus 99% genetically similar to  another Orthopoxvirus, horsepox. Previous studies reported that the experimental vaccine provoked an antibody response but did not cause disease in animal tests and conferred 100% protection. The new paper used human cell lines and mouse models, so it is only EXPLORATORY, but found that the horsepox virus is attenuated up to 1,000-fold more than the vaccinia virus strains, which means it contained a much lower concentration of infectious particles.

Mice given the vaccinia-based vaccine strains often developed severe symptoms, while mice given the experimental horsepox vaccine showed no adverse effects. 

The researchers are now planning phase I human clinical trials to test the safety of the vaccine in people.