Six months ago, as the first vaccines were becoming available, I wrote, “Why Are We Vaccinating People Who Have Recovered From COVID-19?” Now that vaccines are plentiful here, but remain in short supply worldwide, the question is even more pertinent.
People can become immune to viruses through either vaccine immunity or by natural immunity after recovery from infection. Natural viral infection and recovery generally causes better immunity than vaccines.
The public health community argued that people who have recovered from COVID-19 should be vaccinated because the long-term durability of natural immunity is unknown. The Center for Disease Control and Prevention still gives this advice. Yet the durability for vaccine immunity is also unknown. In fact, there is longer follow-up on natural immunity than on vaccine immunity, and it indicates natural immunity to COVID-19 is real and long-lasting. A recent study published in Nature found that “Individuals who have recovered from COVID-19 have a substantially lower risk of reinfection” and that even “mild” COVID–19 infection “induces … long-lived humoral immune memory in humans.”
COVID-19 is caused by a coronavirus—SARS-CoV-2. There are six other coronaviruses with known human chains of transmission: four common cold coronaviruses that circulate endemically and cause mild symptoms and SARS-CoV-1 and MERS-CoV, which in recent decades caused limited outbreaks with relatively high infection fatality rates.
SARS-CoV-1 and MERS-CoV are closely related to COVID-19’s SARS-CoV-2, and natural immunity from them lasts for years. Studies of the endemic cold viruses also indicate long-lasting immunity so that even if reinfection occurs, the resulting disease is mild.
Natural SARS-CoV-2 immunity appears to be similar to the other coronaviruses. Reinfection in the months following initial infections in Qatar was very rare and associated with mild disease. A study of English hospital workers found that recovery from infection, as indicated by positive antibodies, nearly eliminated the risk of new SARS-CoV-2 infection over the following six months.
Now there is definitive evidence that natural immunity is as good or better than vaccine immunity in COVID-19. Researchers at the Cleveland Clinic followed 52,238 health system employees after vaccination started in December 2020. Previously infected, unvaccinated employees had no higher incidence of SARS-CoV-2 infection than vaccinated employees, including those who had been previously infected and those who had not. Not one of the 1,359 previously infected subjects who remained unvaccinated was reinfected. The authors concluded people who previously had COVID-19 are “unlikely to benefit” from vaccination and “vaccines can be safely prioritized to those who have not been infected before.”
There is no point in using vaccines here or worldwide for people who are already immune. While the need and demand for additional vaccines in the U.S. are decreasing, COVID-19 vaccines remain scarce in developing countries. Fewer than 5 percent of people in Africa have been vaccinated and COVID-19 infections and deaths are spiking there. Even India, where many vaccines are made, has vaccinated under 15 percent of its people. Stretching the available supply for developing countries is important.
Confirmed cases who have not yet been vaccinated can hold off. And people who have reason to believe they were infected but do not yet have confirmation should have serology testing and be placed at the back of the queue if the results indicate previous infection and immunity.
Not vaccinating people with natural immunity will protect them from rare severe vaccine side effects like heart inflammation (myocarditis) and blood clots and the more common COVID-19 like symptoms that sometimes follow a second vaccine dose. It will stretch vaccine supplies to maximize the number of people protected. This will benefit all countries. The biggest risk developed countries with high vaccination rates face is the emergence of viral variants that the existing vaccines are ineffective against. Cutting the global circulation of SARS-CoV-2 is the surest way of lowering the likelihood of variant emergence.
Both our knowledge of viral infections in general and coronavirus infections in particular, along with accumulating evidence on COVID-19, indicate that vaccination of people with natural immunity from previous infection makes little sense while there are large numbers of unvaccinated people. The time has come to follow the science. We should stop vaccinating people with natural immunity and redirect vaccines toward those people and countries where they are most needed.