How effective is the original vaccine against Omicron

Ina Research published in Open JAMA Network Today, scientists report on the effectiveness of the original vaccine and booster shot against COVID-19 Delta and Omicron variants.

Researchers in Ontario analyzed data from more than 134,000 people, including those who tested positive for Delta and Omicron infections in December 2021. They found that those who had been vaccinated The full strain (with two doses of vaccine mRNA, from Moderna or Pfizer-BioNTech) reduced the effectiveness of the vaccine against both Delta and Omicron infections, but the decrease was greater for Omicron than against Delta . Among vaccinations, the effectiveness of the shots decreased from 36% until two months after the second dose of the main series, to 1% until four months later (or six months after the second dose).

The booster dose helped restore some of the vaccine’s effectiveness, bringing it back up to 61% from Omicron starting a week after people received the booster shot.

“The key message is that against Omicron, you really need three doses to protect yourself,” said Dr. Jeff Kwong, senior scientist at ICES (a nonprofit research institute) and lead author of the study. optimal protection from serious results. “Two doses were good enough against Delta, but since last December, when Omicron took over, two doses have not provided sufficient protection.”

Read more: I had COVID-19. Do I still need Omicron Booster?

The study did not find out how long that protection lasted after the third shot, or the first booster dose. US health officials now recommend that people receive another booster dose, the first dose specifically targeted at Omicron. The booster contains the genetic sequence of Omicron BA.4/5, which currently causes nearly all new infections of COVID-19. Based on data from his study, which showed reduced protection after the primary vaccination, Kwong predicts that the same will happen after the first booster. If the antibodies weaken, then the person is less protected from infection with the virus.

On the plus side, Kwong’s study confirms previous data showing that vaccinated people who also received their first booster are still protected from becoming seriously ill with COVID-19, even if they contaminated with Omicrons; The vaccine’s effectiveness against severe disease is about 95% a week or more after the third dose. The new one Booster based on Omicron, targeting both the original variant and Omicron BA.4/5, “definitely a good move,” said Kwong, to improve its ability to protect people from infection. However, he says, “my worry is that there might be another variant that comes up with other mutations. And this Omicron booster may or may not help combat that. “

Read more: Should You Combine Omicron Boosters? Here’s what you need to know

The study data are a good reminder that vaccines cannot provide perfect protection, especially against infection, Kwong said. So other measures may be more effective, including wearing masks and avoiding large gatherings in homes with poor ventilation. “We need other measures to better protect ourselves, and wearing a mask is one measure regardless of the variant circulating,” he said. “It’s unfortunate that masks have become politicized, but the more people wear masks, the more people are protected.”

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