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After an average of three to four months, it was found that people who were fully vaccinated had a 73% protection against infection.
An analysis of American patients on Monday stated that two doses of Pfizer vaccine remain highly effective against severe Covid (including the Delta variant) for at least six months.
Although previous clinical trial data showed that jabs can prevent hospitalization, the research published in The Lancet measured the effectiveness of a vaccine over time in a real-world environment.
Pfizer and health care provider Kaiser Permanente reviewed the records of 3.4 million residents in Southern California, about a third of whom were vaccinated between December 2020 and August 2021.
After an average of three to four months, it was discovered that a fully vaccinated person can prevent infection by 73% and hospitalization by 90%.
However, although the protection from Delta infection decreased by 40% within five months, the protection of all variant cases against hospitalization was still very high during the study period.
The study pointed out that the results are consistent with preliminary data from the US and Israeli health authorities.
The authors concluded that the reduced infection defense “may be mainly due to weakened vaccine efficacy, rather than delta variants evading vaccine protection.”
“Our findings emphasize the importance of monitoring the effectiveness of vaccines over time and indicate that a booster dose may be needed to restore the initial substantial protection observed early in the vaccination schedule,” it said.
In August, the United States authorized an additional dose of Covid-19 vaccine for people with weakened immune systems, while in France, it provided additional vaccinations for the elderly.
Israel went further, providing a third dose to children 12 years and older, five months after receiving the second injection.
However, a report from the World Health Organization (WHO) in September found that the current vaccine is sufficiently effective against severe Covid, so the general population does not need a third injection.
The WHO last month called for a moratorium on intensified injections before the end of the year to address the serious inequality in dose distribution between rich and poor countries.
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