What does data say about COVID, vaccines and natural immunity?

Both COVID-19 vaccinations and previous coronavirus infections provide some level of protection against the virus. However, a recently released report from the Centers for Disease Control and Prevention (CDC) showed that vaccination “significantly enhances” immunity for people previously infected with coronavirus.

Additionally, a series of federal and state-level datasets make it easier to compare immunity from vaccines versus a previous infection of COVID-19.

One measure from the CDC tracks the presence of COVID-19 antibodies present in samples from blood donors. The agency then estimates the “proportion of the population with some presumed protection against infection.” The data is limited. The samples represent most — but not all — of the US, and the CDC says that blood donors may be likelier to be more vaccinated than the overall population.

However, the data does show a trend that immunity increased with the introduction of vaccines. In January, the agency estimated 21% of people 16 and older had developed COVID-19 antibodies. Less than 1% of that population had at least one vaccine dose at the time.

By August, the antibodies number rose to an estimated 90% and those receiving at least one vaccine dose climbed to 59%.

At least three state agencies also have published data addressing reinfection rates and vaccinations.

North Carolina had 10,812 COVID-19 cases among those who had previously contracted the virus as of early September. Of those cases, 200 occurred after vaccination.

In Oklahoma, there were 1,094 new cases among every 100,000 previously infected people as of September. During the same period, there were 557 breakthrough cases for every 100,000 fully vaccinated persons.

During the most recent surge in cases, the Alaska Division of Public Health noted in a September report that uninfected people were 5.4 times more likely to get COVID-19 than the previously infected. Among the previously infected, the unvaccinated had a 26% higher case rate than the vaccinated.

Neither the report nor these datasets say precisely how well people are protected against COVID-19 through vaccination, previous infection, or both. However, all could be used to develop an understanding of vaccine effectiveness. Future data releases from the CDC and state agencies can help illuminate understanding further.

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