A study in Germany showed that 81% had preexisting T cell immunity against Covid-19. This might explain why Covid was DOA in Germoney.
Researchers at University Hospital Tübingen in Germany studied the blood of 365 people, 180 of whom had had Covid-19 and 185 who hadn't. When the researchers exposed people's blood to SARS-CoV-2, the virus that causes Covid-19, people who had had the illness already produced the strongest immune response. But surprisingly, there was also an immune reaction in 81 per cent of the people (150) who had never had Covid-19. This, the scientists said, was because they had already been infected with one or more of the common cold coronaviruses known to infect humans - named OC43, 229E, NL63 and HKU1 - and their immune systems cross-reacted as a result. The reaction the researchers were studying is caused by T cells, which are a type of white blood cell that produce long-lasting protection from serious infection.
https://www.researchsquare.com/article/rs-35331/v1
https://www.dailymail.co.uk/news/article-8475639/Catching-colds-protect-Covid-19-scientists-say.html
