Health

Efficacy of booster vaccine dose wanes after 10 weeks – VnExpress


Data from the UK show that booster doses of the vaccine attenuate the ability to prevent symptomatic nCoV infection within 10 weeks of vaccination.

Follow NY Times, The British study, published on December 23, was conducted on people who had received the AstraZeneca, Pfizer or Moderna vaccines. Experts said that in both vaccines, the effect of the booster dose on the Omicron strain was lower than the Delta strain.

In humans who received two doses of AstraZeneca vaccine and a booster dose of Moderna or Pfizer vaccines, the effectiveness in symptom prevention was 60% two to four weeks after injection. However, after 10 weeks, the booster dose of Pfizer was only 35% effective. Moderna booster dose is 45% effective for up to 9 weeks.

For people who received three doses of the Pfizer vaccine, the effectiveness decreased from 70% to 45% in 10 weeks. People who injected two doses of Pfizer and a booster dose of Moderna had better results. The vaccine still provides up to 75% protection for up to 9 weeks.

A new report from the UK Health Security Agency (UKHSA), says: “It takes several weeks to estimate the effectiveness of Omicron against severe symptoms. But based on experience with previous strains, the vaccine still provides protection. significantly”.

Since Omicron was discovered, many studies have shown that the strain is capable of avoiding antibodies produced after vaccination or natural infection. Still, experts believe that booster doses of the vaccine are effective in preventing hospitalizations and deaths.

Healthcare workers prepare a dose of the Covid-19 vaccine in San Rafael, California, September 2021. Photo: NY Times

The report also found that people infected with the Omicron variant were less likely to be hospitalized than those infected with Delta. UKHSA notes that this result should be interpreted with caution, because the number of Omicron infections is not high. As such, the volunteers in the study were not representative of the majority.

The US has recommended that people get a booster dose when the Omicron strain spreads. Israel has just decided to give a fourth dose of the vaccine to high-risk people.

Answer VnExpressDr. Nguyen Huy Luan (Head of Immunization Unit, University of Medicine and Pharmacy Hospital, Ho Chi Minh City) said, The effectiveness of the Covid-19 vaccine over time depends on many factors According to research by British scientists published in November, most vaccines lose their effectiveness after about 6 months. Protection for two doses of Moderna decreased from 90% to 58%. Meanwhile, the Pfizer vaccine reduced effectiveness from 87% to 45%. The effectiveness of the AstraZeneca vaccine decreased from 77% to 67% after 4 months. Vaccine Sputnik V decreased effectiveness from 96% to 31% after 6 months.

“Antibodies after vaccination will gradually decrease after 3-6 months, but can still protect the body by the mechanism of cells. Some studies show that the Covid-19 vaccine can provide protection for up to 11 months. The new strain of Omicron can reduce the effectiveness of the vaccine, and the early administration of additional doses and boosters will help increase the level of protection for each individual and the community, “said Dr. Luan.

In the share posted on ABC In mid-December 2021, Dr. Simone Wildes, infectious disease specialist at Shore Health Health System in Massachusetts, USA, said that the booster dose of vaccine helps restore antibodies after injection to peak levels, effectively preventing Omicron. . “Antibodies peak 10 to 14 days after injection, then everything slows down. Antibodies then decline, but the booster dose will help them stabilize again,” he said.

Currently, 36 countries around the world have injected three doses of Covid-19 vaccine after the basic injection course, according to data published by the National Institutes of Health Our World in Data. Germany, Austria, Canada and France were the first countries to introduce booster shots. According to WHO, booster doses are given to people who have completed primary immunization (one dose or two doses based on the type of vaccine administered), when their immunity and clinical protection have been established. falls below the required level over time. The purpose of booster injection is basically to restore the effectiveness of the vaccine in the body to the required level.

In Vietnam, from the beginning of December, the Ministry of Health also allows a booster injection for those who have completed the basic dose, with an interval of three doses after two and three months.

Thuc Linh – Le Cam

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