Jan 6 (Reuters) - Johnson & Johnson (JNJ.N) said on Thursday that a real-world study showed its single shot COVID-19 vaccine protects against breakthrough infections and hospitalizations for up to six months. The study, sponsored by the vaccine developer, was conducted between Jan. 1 and Sept. 7 last year, before the Omicron variant was discovered. It is also yet to be peer-reviewed. J&J said 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 Inc (PFE.N) and BioNTech"s (22UAy.DE) as well as Moderna (MRNA.O). No waning of protection was found for ICU admissions for all the three vaccines, J&J said. The company said the study was carried out by collecting claims and laboratory data covering 168 million people.