Within weeks, scientists at the Walter Reed Army Institute of Research expect to announce that they have developed a vaccine that protects people from COVID-19 and all its variants, even Omicron, as well as from previous SARS-origin viruses that have killed millions of people worldwide.

While breakthrough infections have increased with the emergence of the delta and omicron variants, the vaccines remain quite effective at preventing hospitalizations and deaths. The success of the new technology has led scientists to try to figure out why mRNA vaccines are so effective and whether the protection they provide is likely to endure as new variants arise.

A new study from researchers at Washington University School of Medicine in St. Louis and St. Jude Children's Research Hospital shines light on the quality of the immune response triggered by mRNA vaccines. The study shows that the Pfizer vaccine strongly and persistently activates a kind of helper immune cell that assists antibody-producing cells in creating large amounts of increasingly powerful antibodies, and also drives the development of some kinds of immune memory. Known as T follicular helper cells, these cells last for up to six months after vaccination, helping the body crank out better and better antibodies. Once the helper cells decline, long-lived antibody-producing cells and memory B cells help to provide protection against severe disease and death, the researchers said.

We performed complete autopsies on 44 patients with COVID-19 to map and quantify SARS-CoV-2 distribution, replication, and cell-type specificity across the human body, including brain, from acute infection through over seven months following symptom onset.

We show that SARS-CoV-2 is widely distributed, even among patients who died with asymptomatic to mild COVID-19, and that virus replication is present in multiple extrapulmonary tissues early in infection. Further, we detected SARS-CoV-2 RNA in multiple anatomic sites, including regions throughout the brain, for up to 230 days following symptom onset.

Despite extensive distribution of SARS-CoV-2 in the body, we observed a paucity of inflammation or direct viral cytopathology outside of the lungs. Our data prove that SARS-CoV-2 causes systemic infection and can persist in the body for months.