WASHINGTON, United States (AFP) — Johnson & Johnson said Wednesday a second dose of its Covid-19 vaccine boosted immunity beyond the first dose. In two clinical studies that have not yet been peer-reviewed, the additional shot evoked a nine-fold increase in antibodies to the coronavirus, the company said in a news release. President Joe Biden’s administration has announced plans for all Americans vaccinated with mRNA vaccines — Pfizer and Moderna — to receive a third […]