Natural immunity after covid-19 infection appears to last for at least the one year in which the virus has been circulating at large. Extrapolating from research on the SARS and MERS coronaviruses, it could be much longer. In one study of 176 people infected with SARS, immunity lasted for an average of two years. Another long-term analysis of health-care workers previously infected with SARS found antibodies up to 12 years later. Protective antibodies for the MERS coronavirus have similarly been documented to last for at least three years. And while the 1918 pandemic was caused by an influenza virus, the immune systems of those infected were able to make antibodies to the virus nearly nine decades later, a 2008 Nature study found.
Even mild infections appear to elicit a persistent and functional immune response. One recent European study found that people who had mild or asymptomatic covid-19 mounted a “robust T-cell immunity” afterward. A separate French study affirmed this, noting that some people who lived with a confirmed covid-infected person developed T-cell immunity even when they did not test positive for covid.
These scientific observations and the growing prevalence of natural immunity in the United States have significant implications for our national vaccine strategy. To maximally preserve human life, we should prioritize our limited vaccine supply to those who have never had covid-19. Given the scarcity of the vaccine, it doesn’t make sense to administer it to those who already had the disease while vulnerable seniors are sitting ducks in this pandemic war.