New research from the Centers for Disease Control and Prevention and health officials in California and New York indicates that a previous case of Covid-19 protected humans from infection better than vaccinations did during the delta wave last summer and fall.
The findings, published Wednesday in the CDC's Morbidity and Mortality Weekly Report, appear to contradict public health announcements pushing for vaccinations.
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But experts argue that the shots remain the safest way to protect against the most serious consequences of Covid. Even below the height of the delta wave last summer, virtually all hospitalized Covid patients were unvaccinated.
"Vaccines continue to reduce a person's risk of contracting the virus that causes Covid-19 and are extremely effective in preventing serious illness," said Benjamin Silk, one of the study's authors and an epidemiologist for infectious diseases at the CDC. during a conversation with journalists. Wednesday.
The new research is based on analyzes of Covid infections among more than 1.1 million adults in California and New York from May to November last year.
This time frame is limited to a period when the highly transmissible delta variant was catching steam, and immunity among the first vaccinated in the early days of last year began to decline. Booster shots were not yet widely available.
As such, the results cannot be applied to the current omicron variant rise, which accounts for more than 99 percent of new Covid cases in the United States.
"Omicron has changed things completely," said Dr. Paul Sax, an infectious disease expert at Brigham and Women's Hospital and Harvard Medical School. The Omicron variant has led to "much higher rates of reinfections and a much higher rate of breakthrough infections," he said.
The CDC is expected to release research on how vaccines and boosters perform against omicron later this week.
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The study was published Wednesday by researchers at the CDC, the California Department of Public Health, the New York State Department of Health and the New York City Department of Health and Mental Hygiene, found that individuals who had been infected with coronavirus were better protected against reinfections during the delta wave than those who had never been infected but had been vaccinated.
And the most robust protection against the delta variant was seen in people who had both been vaccinated and had previously been diagnosed with the virus - sometimes referred to as "hybrid immunity."
However, this level of protection may change as the virus progresses.
"Although the epidemiology of Covid-19 may change with the emergence of new variants, vaccination remains the safest strategy to prevent SARS-CoV-2 infections and associated complications," the study authors wrote.
The number of cases and hospitalizations was highest among people without immunity: those who had never been diagnosed with Covid and were never vaccinated.
And Covid-19 infection comes with serious risks. By the end of the study period, more than 130,000 people in California and New York had died from the disease.
Anyone aged 12 years and older is eligible for a Covid booster shot five months after their last dose of either the Pfizer-BioNTech or Moderna vaccine. A booster for those who originally received the Johnson & Johnson syringe is given after two months.
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