Omicron Appears to Cause Less Severe Illness but Is More Resistant to Pfizer Vaccine

A large study of patients in South Africa found that Pfizer’s COVID-19 vaccine dropped to just 30% effectiveness against the omicron variant, but cases produced just mild illness

A dose of Pfizer's COVID-19 vaccine. Photo: Daniel Pockett/Getty

A large, real-world study of COVID-19 patients in South Africa brought good and bad news about the new, faster-spreading variant omicron: It produces milder symptoms, but is more resistant to Pfizer's vaccine.

The study, from South Africa's largest health insurer Discovery Health, looked at data from 211,000 COVID0-19 cases, 78,000 of which were traced to the omicron variant. Nearly half of the patients had received two doses of Pfizer's COVID-19 vaccine, while the others were unvaccinated.

Among those who were vaccinated, Pfizer's formulation was just 30% effective in preventing infection with omicron, a significant drop from the 80% protection it had against earlier variants. The low numbers indicates that omicron will likely cause a high number of breakthrough infections for people who are vaccinated.

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However, Pfizer's vaccine was still highly effective in preventing severe illness from omicron. The two-dose series still protected people from needing hospitalization 70% of the time: "very good protection," the study authors said.

Additionally, most of the infections with omicron have been mild, with people recovering within three days. After an incubation period of three to four days, patients first reported experiencing a scratchy throat, which then transitions into nasal congestion, a dry cough and muscle aches and pains.

Hospitals have said that most patients they saw with omicron were unvaccinated, and they were less likely to have respiratory issues or require oxygen with this variant compared to past ones like delta.

"What is encouraging at this stage is a flatter trajectory of hospital admissions indicating likely lower severity of this wave," Ryan Noach, Discovery Health's chief executive, said at a press briefing, according to The Washington Post.

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The study did not look at if boosters provided better protection against omicron, as they are not yet available in South Africa. U.S. health experts have urged Americans to get their booster shot as soon as possible now that they are authorized for anyone aged 16 and up who was fully vaccinated at least 6 months prior.

Dr. William Schaffner, professor of infectious diseases at Vanderbilt University Medical Center, tells PEOPLE that with omicron now in the U.S. — and with the delta variant still causing severe illness in unvaccinated people — everyone needs to get their shots.

"We have this large vaccination deficit we need to make up," he says. "We have a lot of people who still haven't gotten dose one. We have a lot of children who are age five and older that need to be vaccinated before we go out and celebrate Christmas with all our family. And then we have a lot of people who are eligible for boosters. They've been coming in steadily, but we need to see even more of them come in."

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