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CDC: Natural immunity stronger than vaccines alone in delta wave

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DENVER (KDVR) — Natural immunity was six times stronger during the delta wave than vaccination, according to a new report from the U.S. Centers for Disease Control and Prevention.

The report, released Jan. 19, analyzed COVID outcome data from New York and California, which account for about one in six of the country’s total COVID deaths.

The study has limitations, namely that it was carried out before the omicron wave and does not take into account any information on the boosters. However, it is broadly in agreement with studies from other countries.

Vaccines were more effective in preventing serious infection or disease than natural immunity against previous infections before the delta variant became the dominant strain. After delta became the main strain, vaccines alone weakened against the virus and natural immunity became much stronger. This could largely be due to the fact that vaccines began to fade around the time delta spread, according to the study.

“Importantly, infection-derived protection was greater after the highly transmissible Delta variant became predominant,” reads the report, “coinciding with the early decline in vaccine-induced immunity in many people”.

In California, during the week of May 30, 2021, COVID-19 case rates were 19.9 times lower in vaccinated people with no previous cases, 7.2 times lower in unvaccinated people with a previous one case of COVID-19 and 9.6 times lower among vaccinated people with a previous case of COVID-19 than they were among unvaccinated people without any previous infection.

At a time when the delta variant was the dominant strain on October 3, it changed. Case rates in vaccinated people without a previous diagnosis of COVID-19 were only 6.2 times lower than those in uninfected and uninfected people – three times less effective than pre-delta people. They increased to 29 times less in unvaccinated people who had already been diagnosed and to 32.5 times in vaccinated people who had already been diagnosed with COVID-19.

Similar numbers came from New York.

The study also follows the same trend with hospitalizations. In California, the increase in critical illness protection was even more dramatic. It shows that the protection offered by previous infections increased ninefold in the delta wave.

The effectiveness of natural immunity with omicron, however, is not yet fully understood. The CDC warns that vaccines and natural immunity have waned with the new dominant variant.