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Pfizer shots offer 70% protection against Omicron hospitalization, study suggests

Seated people waiting for COVID-19 vaccinations
People wait for COVID-19 vaccinations at a hospital in Soweto, South Africa.
(Jerome Delay / Associated Press)

The Omicron variant appears to cause less severe disease than previous versions of the coronavirus, and the Pfizer vaccine seems to offer less defense against infection from it but still gives good protection from hospitalization, according to an analysis of data from South Africa, where the new variant is driving a surge in infections.

While the findings are preliminary and have not been peer-reviewed — the gold standard in scientific research — they line up with other early data about Omicron’s behavior, including that it seems to be more easily transmitted.

Still, some experts cautioned that it’s too soon to draw conclusions about the outcomes since the Omicron variant is still quite new and hospitalizations can lag weeks behind infections.

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Two doses of the Pfizer-BioNTech COVID-19 vaccine appeared to provide just 33% protection against infection during South Africa’s current Omicron-driven wave of cases but 70% protection against hospitalization, according to the analysis conducted by Discovery Health, South Africa’s largest private health insurer, and the South African Medical Research Council.

The study did not look at booster shots, which are not yet prevalent in South Africa but which data from elsewhere have indicated improves protection.

For the record:

9:14 a.m. Dec. 14, 2021A previous version of this story misstated the time span and nature of the study’s data. The period was from Sept. 1 to Dec. 7, not from Nov. 15 to Dec. 7, and not all of the 211,000 coronavirus test results examined were positive.

The analysis in South Africa was based on examining more than 211,000 COVID-19 test results that date from Sept. 1 to Dec. 7 — 41% of which were for adults who had received two doses of the Pfizer vaccine, which is the most commonly used COVID-19 vaccine in South Africa.

The study split the samples up into two periods: those taken before Oct. 31, when Omicron was likely not very prevalent in South Africa, and those from after Nov. 15, when it was gaining ground. The latter group was used as a proxy for measuring the effects of the Omicron variant.

Experts now say that the Omicron variant accounts for more than 90% of all new infections in South Africa, Discovery Health chief executive Ryan Noach said.

The country is experiencing rapid community spread of the coronavirus, concentrated in its most populous province, Gauteng. The seven-day rolling average of daily new cases in South Africa has risen over the last two weeks from 8.07 new cases per 100,000 people Nov. 29 to 34.37 new cases per 100,000 people Monday, according to Johns Hopkins University. The death rate hasn’t increased during that same period.

“The Omicron-driven fourth wave has a significantly steeper trajectory of new infections relative to prior waves. National data show an exponential increase in both new infections and test positivity rates during the first three weeks of this wave, indicating a highly transmissible variant with rapid community spread of infection,” Noach said.

Pfizer says a booster dose of its COVID-19 vaccine may protect against the new Omicron variant, which early indications show might be more contagious.

Although case numbers are rising, hospitalizations are not increasing at the same rate, leading the scientists to report that the risk of hospitalization from Omicron is lower than from Delta or earlier variants. Hospital admissions for adults diagnosed with COVID-19 are 29% lower compared with the wave that South Africa experienced in mid-2020, after adjusting for vaccination status, according to the analysis.

The results show that people who received two doses of the Pfizer vaccine had 33% protection against infection in the first weeks of South Africa’s current Omicron-driven wave. That’s a significant drop from the 80% protection against infection afforded during earlier periods.

The researchers say it’s encouraging that the results show people fully vaccinated with Pfizer shots had 70% protection against hospital admission during the Omicron-driven surge. That’s still a drop from the 93% protection seen in South Africa’s Delta-driven wave.

The study shows that significant protection against hospital admission continued even among older groups, with 67% protection in people ages 60 to 69 and 60% in people ages 70 to 79.

While jabs and boosters are offered in the U.S. and much of Europe, vaccination rates remain low in southern Africa, where the Omicron variant was first detected.

But some say there’s still not enough data to draw broad conclusions about hospitalizations and the severity of disease caused by Omicron.

“Their analysis covers just three weeks of data. Thus, it is important to avoid inferring too much right now,” Dr. Michael Head, senior research fellow in global health at England’s University of Southampton, wrote of the study.

Although South Africa’s findings indicate that Omicron may cause milder disease, reports from Denmark show the opposite, he wrote. There are many variables that can affect the findings, including any previous infection, potentially waning immunity and the age range of people infected so far.

“Is Omicron milder or more severe than Delta?” Head wrote. “Time will tell. The world’s finest scientists, including many in the global south such as in South Africa, will find out. For now, national-level decision-makers have to consider that discretion is the better part of valor.”

The South African analysis supports an earlier assessment by British authorities.

Britain’s Health Security Agency said Friday that new data confirmed that Omicron is more easily transmissible than other variants. Other studies suggest that both the AstraZeneca and Pfizer vaccines are less effective in preventing symptomatic infections in people exposed to Omicron, but preliminary data show that effectiveness appears to rise to between 70% and 75% after a booster shot.

The South Africa study also found that Omicron poses a higher risk of reinfection. For individuals who have previously had COVID-19, the risk of reinfection with Omicron is significantly higher than that of earlier variants.


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