COVID-19 vaccine gives 5 times the protection of 'natural immunity,' data show

SARS-CoV-2 viruses highly magnified
SARS-CoV-2 viruses highly magnified


US adults who previously had COVID-19 contracted the disease at more than five times the rate of those who were fully vaccinated, according to data published today in Morbidity and Mortality Weekly Report (MMWR).

Rolling out vaccines during a pandemic is not easy, and people can get confused by evidence that shows COVID vaccines don't work perfectly, including a study yesterday showing that household spread with the Delta (B1617.2) variant still happens after vaccination, albeit not as readily in the unvaccinated and not leading to severe cases (see today's CIDRAP News story).

Yet the body of evidence continues to grow that, despite their imperfections, COVID-19 vaccines continue to work very well, and today's study adds to that. Officials with the Centers for Disease Control and Prevention (CDC), who led the study, say of the results, "All eligible persons should be vaccinated against COVID-19 as soon as possible, including unvaccinated persons previously infected with SARS-CoV-2."

Unvaccinated at 5.5 times the risk

The researchers looked at data from nine states on 201,269 hospitalizations for COVID-like illness from Jan 1 to Sep 2, 2021. Of these, 94,264 previously had molecular testing for SARS-CoV-2, and 7,348 (7.8%) had had at least one other SARS-CoV-2 test result 14 or more days before hospitalization and were thus included in the study.

Among that group, 1,020 hospitalizations were among previously infected and unvaccinated people, and 6,328 cases were among fully vaccinated people who were not previously infected. A recent lab-confirmed COVID-19 infection was found in 324 (5.1%) of the fully vaccinated people and in 89 (8.7%) of the unvaccinated, previously infected people.

In comparing unvaccinated people who were infected 90 to 179 days after a previous infection compared with those who were vaccinated 90 to 179 days before their COVID infection, the researchers found the incidence of infection to be 5.49 times higher in the unvaccinated (95% confidence interval, 2.75 to 10.99).

The authors conclude, "These findings suggest that among hospitalized adults with COVID-19–like illness whose previous infection or vaccination occurred 90–179 days earlier, vaccine-induced immunity was more protective than infection-induced immunity against laboratory-confirmed COVID-19."

Daily cases near 100,000

In what could be an anomaly, the United States reported 99,384 new cases yesterday and 1,776 deaths, according to the Johns Hopkins COVID-19 tracker. The day before officials noted 76,957 new COVID-19 cases and 2,141 deaths. All told, the country now has had 45,892,544 COVID cases and 744,955 deaths.

The 7-day average of new daily COVID-19 cases is 72,569, with 1,381 daily deaths, according to the New York Times tracker.

And the CDC COVID Data Tracker shows that 57.8% of Americans are now fully vaccinated against COVID-19, 66.5% have received at least one dose of vaccine, and 8.7% of fully vaccinated people have received a booster dose.

Pandemic economic impact

Hamstrung by COVID-19 and supply shortages, the US economy slowed sharply to a 2% annual growth rate in July through September, the lowest quarterly growth since the recovery from the pandemic recession began last year, the Associated Press reported.

In other industry news, the Biden administration's vaccine mandate for private-sector employers will allow companies to force workers who refuse to get the COVID-19 vaccine to pay for required weekly tests and masks, Bloomberg News reports.

New York City is bracing for a shortage of police and firefighters as its COVID vaccination deadline approaches today, according to the New York Times. And Citigroup says that US-based employees must submit proof of COVID vaccination by Jan 14 if they want to stay employed, according to CNN.

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