New studies suggest a vaccine after infection can give 'bulletproof' immunity Two studies show evidence that natural immunity can last at least a year against the Alpha variant, but the strength of immunity is unclear against other variants. Author: Chris Hrapsky Updated: 10:53 PM CDT July 25, 2021 GOLDEN VALLEY, Minn. — Four new studies are helping to answer just how protected people are after a coronavirus infection and how potent a vaccine can be after infection. The research shows good evidence that natural immunity lasts at least a year and could last much longer, according to experts, but it’s unclear if the protection is enough to neutralize several variants of the SARS-CoV-2 virus.