[1][5] In 2020, Kulldorff was a co-author of the Great Barrington Declaration, which advocated lifting COVID-19 restrictions on lower-risk groups to develop herd immunity through infection before vaccines became available, while promoting the fringe notion that vulnerable people could be simultaneously protected from the virus.

[6][7][8][9] The declaration was widely rejected, and was criticized as being unethical and infeasible by Tedros Adhanom Ghebreyesus, the director-general of the World Health Organization.

[10] During the pandemic, Kulldorff opposed disease control measures such as vaccination of children, lockdowns, contact tracing, and mask mandates.

[1][14] He moved to the United States for his postgraduate studies as a Fulbright fellow,[1] obtaining a doctorate in operations research from Cornell University in 1989.

[14] His doctoral thesis, titled Optimal Control of Favorable Games with a Time Limit, was written under the direction of David Clay Heath.

[11] In December 2021, Kulldorff became one of the first three fellows, along with Bhattacharya and Scott Atlas, at the Academy for Science and Freedom, a program of the private, conservative Hillsdale College, a liberal arts school.

His efforts resulted in the Great Barrington Declaration, an open letter co-authored with Oxford’s Sunetra Gupta and Stanford’s Jay Bhattacharya for the AIER.

[31][8][32][33][34] Scientists dismissed the policy as impossible in practice, unethical and pseudoscientific,[6] warning that attempting to implement it could cause many unnecessary deaths with the potential of recurrent waves of disease spread as immunity decreases over time.

Instead, the authors wrote that "[w]ith the new CDC guidelines, strategic age-targeted viral testing will protect older people from deadly COVID-19 exposure and children and young adults from needless school closures".

[42] At the time the video was published, the Centers for Disease Control recommended universal indoor masking for children two years and older.