Natural Immunity Better Than Protection From COVID-19 Vaccination: Study

People with protection against COVID-19 following recovery from the illness were better protected than those who received a COVID-19 vaccine, according to a new study.

People who received a vaccine were nearly five times as likely as the naturally immune to test positive for COVID-19 during the Delta era and 1.1 times as likely to test positive for COVID-19 during the Omicron era, researchers in Estonia found.

The vaccinated were also seven times as likely to be admitted to a hospital for COVID-19 amid the spread of the Delta variant and two times as likely to be admitted to a hospital during the Omicron period, when compared with the naturally immune, the researchers found.

“Our study showed that natural immunity offers stronger and longer-lasting protection against infection, symptoms, and hospitalization compared to vaccine-induced immunity,” Dr. Anneli Uusküla, with the Department of Family Medicine and Public Health at the University of Tartu, and her co-authors wrote.

Previous studies have also found that post-infection immunity is superior to or similar to the protection bestowed by vaccines.

Dr. Uusküla and her colleagues said they felt there were gaps in the literature on the subject, prompting them to work on the study.

They drew from a pool of 329,496 adults and matched many of the adults in three cohorts. One compared people with natural immunity to those who received a vaccine; one compared the naturally immune to people who did not have documented prior infection or vaccination; and one compared the naturally immune to people with hybrid immunity, or both prior infection and vaccination.

People were defined as vaccinated if they had received a full primary series of a COVID-19 vaccine and did not have a documented infection.

The primary outcome was laboratory-confirmed COVID-19 occurring at any time for people without any immunity, after 60 days of recovery from a prior infection for the naturally immune, at least 14 days after completion of a vaccine for the vaccinated group, and at least 14 days after vaccination or 60 days after recovery for people with hybrid immunity.

The second outcome, hospitalization, was defined as hospitalization with COVID-19 and with certain medical codes.

Researchers utilized national health care records and examined data from between Feb. 26, 2020 and Feb. 23, 2022. The Delta era ended in December 2021.

In the cohort comparing the naturally immune to people without prior immunity or vaccination, researchers found that the naturally immune were much better protected against hospitalization, used as a measure of protection against severe disease.

“During both periods, natural immunity proved to be highly effective in protecting against reinfections progressing to severe disease and was associated with a significantly lower risk of COVID hospitalization than no SARS-CoV-2-specific immunity,” the researchers said.

But they also discovered that the naturally immune, while much less likely to be infected during the Delta era, were actually more likely to test positive during the Omicron era.

In the comparison of the naturally immune to people with hybrid immunity, the researchers determined those with hybrid immunity were better protected against infection during the Delta era, but they were at slightly higher risk during the Omicron period. In the hybrid immunity group, just one COVID-19 hospitalization was recorded, compared to nine among the naturally immune.

“Irrespective of the infection-causing variant, the protective effect of hybrid immunity in preventing infection progression to severe COVID-19 significantly exceeded that of natural immunity (although the absolute numbers of hospitalizations in the hybrid immunity subcohort were small),” the authors said.

Limitations included some people being admitted to hospitals with COVID-19 but not for it, though researchers tried minimizing the issue by only including hospitalizations with codes indicating patients had respiratory disease.

The research was funded by the European Regional Development Fund, Estonian Research Council, and European Social Fund.

Authors declared no competing interest.