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‘The Power of Natural Immunity’: COVID Challenge Trials Struggle to Infect Participants, Even at High Doses

By Brenda Baletti, Ph.D.


Scientists trying to reinfect people with the COVID-19 virus so they could test vaccines and treatments found high levels of immunity made it nearly impossible, according to results from the COVID-19 “Human Challenge” trials in the U.K

The results published May 1 in The Lancet Microbe, “raise questions about the usefulness of COVID-19 challenge trials for testing vaccines, drugs and other therapeutics,” Nature reported.

If you can’t get people infected, then you can’t test those things,” Tom Peacock, Ph.D., a virologist at Imperial College London, told Nature.

Brian Hooker, Ph.D., chief scientific officer for Children’s Health Defense told The Defender, “The results show the power of natural immunity as compared to the many breakthrough infections in ‘naive’ vaccinated individuals.”

“Any assertion that vaccination-based immunity is more powerful than natural immunity is complete lunacy — the acquired immune system is a beautiful thing and vaccination is a cheaper and much less effective substitute,” he said.

Challenge trials require deliberately infecting healthy people with a virus, typically so scientists can understand infections and test the effectiveness of existing vaccines and treatments, and develop new ones.

When the U.K. government announced the first human COVID-19 trials in 2021, they were highly controversial.

Proponents argued the trials were necessary to speed the development of countermeasures and that the low relative risk was worth the benefit. Critics countered it was unethical to infect people with a disease for which there is no cure.

After months of ethical debate, the first study launched in March 2021. In that study, researchers exposed 36 people ages 18-29 to the original strain of COVID-19 via nasal droplets.

About 53% of the participants eventually tested PCR-positive for COVID-19 but had very mild or no symptoms. And there was no correlation between symptom severity and viral load…



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