Pfizer says 3 of its shots work against Omicron, citing lab tests, but that 2 appear less effective

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Nurse Samantha Reidy gives Alan Kramer, 74, a cancer patient, his Pfizer-BioNTech Covid-19 booster shot at Hartford Hospital in Hartford, Connecticut on August 24, 2021.
A man receives a booster shot with the Pfizer COVID-19 vaccine in Hartford, Connecticut.JOSEPH PREZIOSO/AFP/Getty Images
  • Pfizer and BioNTech new data about how their vaccine works against the Omicron variant.

  • They said that two doses produced fewer antibodies against Omicron than against other variants.

  • But, they said, a third dose significantly improved the immune response — a hopeful sign.

Pfizer and BioNTech said Wednesday that their vaccine against the coronavirus appeared effective against the Omicron variant under a three-dose regime, but that two doses alone produced a much lesser response.

The companies gave the update in a press release describing lab tests that sought to assess the effectiveness of the vaccine against Omicron, a new and fast-spreading variant discovered last month.

The tests compared the level of protective antibodies against Omicron after two and three doses. The early data provides an indication of how well the vaccines combat the virus, though it is not a perfect test.

The companies — as well as scientists around the world — are racing to figure out how Omicron behaves and how well vaccines will hold up against it. The variant is causing worry because of its large array of mutations.

As part of the news release, Pfizer CEO Albert Bourla said: "Although two doses of the vaccine may still offer protection against severe disease caused by the Omicron strain, it's clear from these preliminary data that protection is improved with the third dose of our vaccine,"

Here are the findings in summary:

  • People who received two doses of Pfizer's vaccine had, on average, 25 times fewer neutralizing antibodies against Omicron as against the original strain of the coronavirus.

  • A month after a third dose of the vaccine, the level of neutralizing antibodies against Omicron rose back up to the levels seen after two doses of vaccine against the original strain.

  • CD8+ T cells, other immune cells that don't depend on antibodies to kill the virus, can still recognise about 80% of the targets on the Omicron that they saw with the original strain.

  • The level of these CD8+ cells is also higher after a third dose of vaccine.

Early evidence suggests the Omicron variant may be easier for people to catch than the Delta variant, but could result in less serious infections.

Pfizer is working on an updated vaccine to target the Omicron variant.

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