Data Suggests Omicron Is Better At Evading Vaccines, But Milder

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The omicron variant is offering more hints about what it may have in store as it spreads around the globe: A highly transmissible virus that may cause less severe disease, and one that can be slowed — but not stopped — by today’s vaccines.

An analysis Tuesday, December 14, 2021, of data from South Africa, where the new variant is driving a surge in infections, suggests the Pfizer vaccine offers less defense against infection from omicron and reduced, but still good, protection from hospitalization.

The findings are preliminary and have not been peer-reviewed — the gold standard in scientific research — but they line up with other early data about omicron’s behavior, including that it seems to be more easily spread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

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

U.S. health officials estimate that a small, but growing proportion of new COVID-19 infections are due to the omicron variant and that the rise is particularly dramatic in some places.

Two weeks ago, the omicron variant accounted for less than 0.5% of the coronaviruses that were genetically sequenced in the U.S. That rose to about 3% last week, the Centers for Disease Control and Prevention reported Tuesday.

But it varies from place to place and is as high as 13% in the New York/New Jersey area, according to the agency.

The CDC is tracking how fast the percentage doubles, and as more cases come in, may be better able to predict whether — or when — the omicron variant becomes the dominant version of the coronavirus in the U.S, health officials say.

In the new South Africa findings, people who received two doses of the Pfizer-BioNTech vaccine appeared to have just 33% protection against infection, compared to those who were unvaccinated, during the country’s current omicron-fueled surge, but 70% protection against hospitalization. The analysis was 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 has indicated improves protection.

The Pfizer vaccine’s 70% protection against hospital admission during the omicron surge compares to a 93% protection level seen in South Africa’s delta-driven wave, according to the new analysis.

That’s a big drop in vaccine protection from a severe illness requiring hospitalization, said Dr. Eric Topol, head of the Scripps Research Translational Institute.

“What we don’t know yet is whether the booster will restore that back to greater than 90% and for how long,” Topol said.

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 one 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 omicron accounts for more than 90% of all new infections in South Africa, according to Discovery Health chief executive Dr. Ryan Noach, and it is also picking up steam in other countries.

Researchers around the world are rushing to figure out what the variant will mean for the coronavirus pandemic, now well into its second year. More information came Tuesday from Pfizer, which announced that its experimental pill to treat COVID-19 — separate from it its vaccine — appears effective against omicron.

In the weeks since the variant was detected, South Africa has experienced rapid spread of the virus. The seven-day rolling average of daily new cases in the country rose over the past two weeks from 8.07 new cases per 100,000 people on Nov. 29 to 34.37 new cases per 100,000 people on Dec. 13, according to Johns Hopkins University. The death rate hasn’t increased during that same period.

Many are now looking to South Africa for clues about what the world could be in for.

“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.

Although case numbers are rising, hospital admissions for adults diagnosed with COVID-19 are 29% lower compared to the wave that South Africa experienced in mid-2020, after adjusting for vaccination status, according to the analysis.

The study indicated significant protection against hospital admission even among older age groups, with 67% for people aged 60 to 69 and 60% for people aged 70 to 79.

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

“Their analyses cover 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, 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?” asked Head. “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 U.K. authorities.

The U.K. Health Security Agency said Friday that new data from the U.K. confirm 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, though preliminary data show that effectiveness appears to rise to between 70% and 75% after a third booster dose.

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