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


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 had molecular testing for SARS-CoV-2, and 7,348 (7.8%) had lab-confirmed COVID-19. 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.

Lab-confirmed COVID-19 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).