Johnson & Johnson said its single-dose vaccine protects against breakthrough COVID-19 for up to six months. Citing a study that it sponsored, Johnson & Johnson said in a release Thursday that protection against infection from its single-dose vaccine starts to wane only from the fourth month compared to the second month in the case of two-dose vaccines from rivals Pfizer and Moderna, which use mRNA technology whereas the J&J shot uses an adenovirus. The study was conducted between Jan. 1 and Sept. 7, and it was before the Omicron variant was discovered in late November. Published in MedRxiv, the study hasn’t been peer-reviewed. No waning of protection was found for ICU admissions for all three vaccines, J&J said. The company said the study was carried out by collecting claims and laboratory data covering 168 million people. “We continue to undertake extensive efforts to study the durability of protection offered by the Johnson …