DENVER (KDVR) – Natural immunity was six times stronger during the delta wave than vaccination, according to a new report from the US Centers for Disease Control and Prevention.
That report, published January 19thanalyzed 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 limits – it was done before the omicron wave and does not take into account any information about boosters. However, this is broadly in line with studies from other countries.
Vaccines were more effective in preventing infection or serious illness than natural immunity from previous infections before the delta variant became the predominant strain. After delta became the main strain, vaccines alone became weaker against the virus and the natural immunity became much stronger. This may be largely due to the fact that vaccines began to decline around the time the delta spread, according to the study.
“Importantly, infection-derived protection was greater after the highly transmissible Delta variant became prevalent,” the report reads, “coinciding with early declines in vaccine-induced immunity in many individuals.”
In California in the week beginning May 30, 2021, the number of cases of COVID-19 was 19.9 times lower among vaccinated individuals without a previous case, 7.2 times lower among unvaccinated persons with a previous case of COVID-19 and 9.6 times lower among vaccinated individuals with a previous case of COVID-19 than they were among unvaccinated individuals without any previous infection.
At a time when the delta variant was the dominant strain on October 3, that changed. The number of cases in vaccinated humans without a previous COVID-19 diagnosis was only 6.2 times lower than in unveiled, uninfected humans – three times less effective than pre-delta. They grew to 29-fold lower among unvaccinated individuals with a previous diagnosis and 32.5-fold among vaccinated individuals with a previous diagnosis of COVID-19.
Similar numbers came from New York.
The study also follows the same trend with admissions. In California, the leap in protection from serious illness was even more dramatic. It shows that the protection from previous infections increased nine times in the delta wave.
However, the effectiveness of natural immunity with omicron is not fully understood yet. The CDC warns that both vaccines and natural immunity have declined with the new dominant variant.
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