The effectiveness of Pfizer and Modern mRNA vaccines against covid infection was 91 percent. However, a recent study by US health workers found that the rate had dropped to 66 percent after the spread of Delta variant infections.
The Centers for Disease Control and Prevention (CDC) in the United States has been monitoring the effectiveness of vaccines in large-scale vaccination of health workers and emergency workers since the vaccines were approved.
Healthcare workers in six states of the country are tested every week on the basis of Covid-19 symptoms. Through this, the researchers tested the effectiveness of the vaccine against asymptomatic and asymptomatic covid infections.
From December 14, 2020 to April 10, 2021, the researchers found that the vaccine’s efficacy rate was 91 percent, based on the number of people who had or had not been vaccinated during the initial period of the study and the length of time they had been monitored.
However, in the weeks leading up to August 14, when more contagious delta variants spread at a higher rate, the effectiveness of the vaccine dropped to 66 percent.
Researchers say there may be a number of reasons why the vaccine’s effectiveness is declining. This includes the fact that the vaccine’s effectiveness has declined over time. On top of that, the issue of an 66 percent efficacy rate has come up in a very small number of people tested for infection in a very short period of time.
Several more recent studies have shown that the efficacy rate of the vaccine against the Delta variant has decreased, but the results of different studies have shown different efficacy rates.
A recent CDC study of patients in New York found that while vaccines have reduced their effectiveness against infections, they still provide more than 90 percent protection against serious illness.
Another CDC study of patients in Los Angeles found that people who had not been vaccinated were 29.2 percent more likely to be hospitalized with covid than those who had been vaccinated.
The Delta variant has the highest number of covid victims in the United States since early July.
A recent study published in the Journal of Virology found that the first test of covid infected people in 2020 showed a thousand times more viruses than those infected with the delta variant.