COVID-19
Immunity
The immune response by humans to CoV-2 virus occurs as a combination of the cell-mediated immunity and antibody production,[275] just as with most other infections.[276] Since SARS-CoV-2 has been in the human population only since December 2019, it remains unknown if the immunity is long-lasting in people who recover from the disease.[277] The presence of neutralizing antibodies in blood strongly correlates with protection from infection, but the level of neutralizing antibody declines with time. Those with asymptomatic or mild disease had undetectable levels of neutralizing antibody two months after infection. In another study, the level of neutralizing antibodies fell four-fold one to four months after the onset of symptoms. However, the lack of antibodies in the blood does not mean antibodies will not be rapidly produced upon reexposure to SARS-CoV-2. Memory B cells specific for the spike and nucleocapsid proteins of SARS-CoV-2 last for at least six months after the appearance of symptoms.[277]
There is immunity provided by nature, that prepares us against an already illness
Reinfection with COVID-19 is possible but uncommon. The first case of reinfection was documented in August 2020.[278] A systematic review found 17 cases of confirmed reinfection in medical literature as of May 2021.[278]
One of the slides [in Internal CDC document] states that there is a higher risk among older age groups for hospitalization and death relative to younger people, regardless of vaccination status. Another estimates that there are 35,000 symptomatic infections per week among 162 million vaccinated Americans.
Vaccinated people infected with delta have measurable viral loads similar to those who are unvaccinated and infected with the variant.
“I finished reading it significantly more concerned than when I began,” Robert Wachter, chairman of the Department of Medicine at the University of California at San Francisco, wrote in an email.
CDC scientists were so alarmed by the new research that the agency earlier this week significantly changed guidance for vaccinated people even before making new data public.
https://www.washingtonpost.com/health/2021/07/29/cdc-mask-guidance/