Study Shows Prior COVID Infection Was Best Protection from Delta Surge, but Vaccines Helped Too

A significant new study is showing that natural immunity from a previous COVID infection provided the best protection against the Delta variant.

And Americans who had a prior bout of COVID-19 and later received the vaccinations were even better protected against Delta than those who just received the inoculations alone. 

Numerous media outlets report the research by the Centers for Disease Control and Prevention suggested that natural immunity was a more potent shield than vaccines against the variant.

Agence France-Presse reports, “During America’s last surge of the coronavirus driven by the Delta variant, people who were unvaccinated but survived Covid were better protected than those who were vaccinated and not previously infected.” 

Johns Hopkins researcher Dr. Marty Makary tweeted this takeaway from the new study: “The data are now abundantly clear. Natural imm(unity) is more effective than vax imm(unity).”

The study examined infections in New York and California last summer and fall and found people who were both vaccinated and had survived a prior bout of COVID-19 had the most protection.

The Washington Examiner’s Jerry Dunleavy noted the report is significant because natural immunity isn’t always counted as valid protection by officials who enforce vaccine mandates. He tweeted, “Important to note that prior infection and natural immunity are not taken into account whatsoever when it comes to vaccine mandates such as the one in Washington, D.C.”

The CDC, which released its U.S. Centers for Disease Control and Prevention (CDC) Morbidity and Mortality Weekly Report, noted several caveats to the research, but added that “vaccination remains the safest and primary strategy to prevent SARS-CoV-2 infections, associated complications, and onward transmission.”

“The bottom line message is that from symptomatic COVID infection you do generate some immunity,” said immunologist E. John Wherry of the University of Pennsylvania. “But it’s still much safer to get your immunity from vaccination than from infection.”

The results do not apply to the Omicron variant of the virus, which now accounts for 99.5% of COVID-19 cases in the United States, according to Reuters. 

The researchers looked at infections in California and New York, which together account for about 18% of the U.S. population. They also looked at COVID-19 hospitalizations in California.

Overall, about 70% of the adults in each state were vaccinated; another 5% were vaccinated and had a previous infection. A little under 20% weren’t vaccinated, and roughly 5% were unvaccinated but had a past infection.

The researchers looked at COVID-19 cases from the end of last May until mid-November and calculated how often new infections happened in each group. As time went on, vaccine-only protection looked less and less impressive.

By early October, compared with unvaccinated people who didn’t have a prior infection, case rates were:

• 6-fold lower in California and 4.5-fold lower in New York in those who were vaccinated but not previously infected.
• 29-fold lower in California and 15-fold lower in New York in those who had been infected but never vaccinated.
• 32.5-fold lower in California and 20-fold lower in New York in those who had been infected and vaccinated.

But the difference in the rates between those last two groups was not statistically significant, the researchers found.

Hospitalization data, only from California, followed a similar pattern.

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