During the recent delta-driven coronavirus wave in the United States, unvaccinated people who survived COVID-19 were better protected than those who were previously vaccinated and uninfected, according to a new study published last week.
The finding adds to the debate about the relative strength of natural immunity compared to that acquired by the SARS-CoV-2 vaccine and is endorsed by the United States’ Centers for Disease Control and Prevention of Diseases (CDC).
Getting infected is not a good strategy
However, the paper’s authors warned against relying on infection as a strategy to acquire immunity because the risk of hospitalization, long-term effects and death is higher in unvaccinated individuals compared to those who are vaccinated.
“The level of protection of vaccination and survival after a previous infection changed during the study period. Vaccination remains the safest strategy for protection against COVID-19,” the CDC said in a statement.
Study conducted prior to booster vaccinations
The analysis was performed before booster injections became widely available and also before the appearance of the Omicron variant, for which immunity to both the vaccine and previous infection appeared to be declining.
The new study enrolled patients between May 30 and November 30, 2021 in New York and California.
For the week of October 3, case rates among vaccinated individuals with no prior COVID-19 were about six times lower in California and five times lower in New York than among unvaccinated individuals with no prior COVID-19.
But infection rates were significantly lower in people with prior COVID-19 disease than in those who had been unvaccinated and had COVID-19, up to 29 times in California and 15 times in New York in unvaccinated people with a prior diagnosis .
Change in Protection Ratio
Before Delta became dominant, vaccination conferred greater immunity than infection itself. But the ratio changed when the variant became dominant in late June and July.
The highest protection in the study was among those with vaccines and prior COVID-19, and hospitalization rates followed a similar pattern.
Other research, including a notable paper from Israel in August, also found that natural immunity was stronger than vaccines during the delta rise.
But the US CDC had previously taken the opposite position based on pre-delta data.
“Further studies are needed to determine the duration of protection from prior infection by variant type, severity and symptomatology, including the Omicron variant,” the article concluded.