Pfizer COVID-19 Vaccine Protects for 6 Months or More, Study Shows

Damian McNamara
April 01, 2021

The Pfizer/BioNTech COVID-19 vaccine affords at least 6 months of protection after the second dose, the companies announced today.

The vaccine was 91.3% effective against COVID-19 in an analysis of 927 symptomatic people through March 13, as indicated by real-world data compiled since the vaccine was given emergency use authorization. This compares to 95% efficacy reported in the interim results that were announced on November 18, 2020.

Furthermore, data released today show that the vaccine affords 100% protection against severe COVID-19, as defined by the US Centers for Disease Control and Protection.

The vaccine was likewise effective in preventing COVID-19 in South Africa, where the variant of concern B.1.351 was first identified.

'Very Encouraging' Finding

"Real-world data are often different than what was found in clinical trials. That is because the people enrolling in clinical trials have to meet certain inclusion and exclusion criteria," John Segreti, MD, told Medscape Medical News.

"Often the real-world results are worse than the trial results. This finding is therefore very encouraging," said Segreti, hospital epidemiologist, medical director of infection control and prevention, and professor of internal medicine at Rush Medical College, Chicago, Illinois.

"The finding that efficacy lasts at least 6 months is not surprising," he added, but it is "very encouraging."

William Schaffner, MD, agreed that this is "very good news." The 6-month duration of protection and the vaccine's efficacy against the South African variant make "the light at the end of the tunnel a little bit brighter," he told Medscape Medical News when asked to comment. Schaffner is professor of medicine in the Division of Infectious Diseases, Vanderbilt University Medical Center, Nashville, Tennessee.

"We're delighted that we can now say rather firmly that it will last at least 6 months. That's how much we can measure securely at the present time, and the clock is still running," he said. The trial is ongoing.

Protection Against Major Variant

The South African variant "has been the most concerning variant so far," Segreti said. "While current vaccines may be less effective in preventing infection with this variant, the finding that the vaccine is effective in decreasing hospitalizations and death is very important news," he said. He noted that it should convince more people to get vaccinated.

Schaffner said he was "a little more cautious" but that "it's great that it offers protection against the South African variant." He said that repeated infections have been reported in that country, "so that's the one we're most worried about.

"If Pfizer's antibodies really do provide some protection ? maybe even a lot of protection ? against this strain, that would be a terrific bonus," he said.

Schaffner pointed out that it is unknown whether the finding is generalizable to the Moderna or Johnson & Johnson vaccine. "We can feel a degree of comfort that at least the Pfizer product does also protect against the South African strain, and we're really quite sure it will protect against the British strain ? that would reduce the need for us to have a booster program right away."

Details From the Data Release

The 91.3% vaccine efficacy rate comes from a total 850 COVID-19 cases identified in the placebo group, vs 77 cases in the cohort that received the Pfizer/BioNTech vaccine.

Investigators reported 32 cases of severe COVID-19, all of which occurred in the placebo group.

The companies noted that efficacy was generally consistent with regard to age, gender, race, and ethnicity and among participants with a variety of underlying conditions.

In South Africa, where the B.1.351 lineage is prevalent, 800 participants were enrolled. Nine cases of COVID-19 occurred, all in the placebo group, yielding an efficacy rate of 100% (95% CI, 53.5 – 100.0).

In addition, no serious safety problems occurred in participants up to 6 months after receiving the second dose.

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Reviewed on 4/2/2021
SOURCE: Medscape, April 01, 2021.

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