Most of the world's vaccines likely won't prevent infection from Omicron

The Pfizer and Moderna shots use the new mRNA technology, which has consistently offered the best protection against infection with every variant. All of the other vaccines are based on older methods of triggering an immune response.

The Chinese vaccines Sinopharm and Sinovac — which make up almost half of all shots delivered globally — offer almost zero protection from omicron infection. The great majority of people in China have received these shots, which are also widely used in low- and middle-income countries such as Mexico and Brazil.

A preliminary effectiveness study in Britain found that the Oxford-AstraZeneca vaccine showed no ability to stop omicron infection six months after vaccination. Ninety percent of vaccinated people in India received this shot, under the brand name Covishield; it has also been widely used across much of sub-Saharan Africa, where COVAX, the global COVID vaccine program, has distributed 67 million doses of it to 44 countries.

Researchers predict that Russia’s Sputnik vaccine, which is also being used in Africa and Latin America, will show similarly dismal rates of protection against omicron.

Demand for the Johnson & Johnson vaccine had been surging in Africa, because its single-shot delivery regimen makes it easy to deliver in low-resource settings. But it too has shown a negligible ability to block omicron infection.

Antibodies are the first line of defense induced by vaccines. But the shots also stimulate the growth of T cells, and preliminary studies suggest that these T cells still recognize the omicron variant, which is important in preventing severe disease.

“What you lose first is protection against asymptomatic mild infection, what you retain much better is protection against severe disease and death,” said John Moore, a virus expert at Weill Cornell Medicine in New York. He called it “a silver lining” that omicron so far appears less lethal than the delta variant.

But this protection will not be enough to prevent omicron from causing global disruption, said J. Stephen Morrison, director of the Global Health Policy Center at the Center for International and Strategic Studies.

“The sheer scale of infection will overwhelm health systems, simply because the denominator will be potentially so big,” he said. “If you have a burst of infection worldwide, a shock, what does the world look like on other side of it? Is it, ‘The war is over,’ or, ‘The war has just entered another phase’? We haven’t begun thinking about any of that.”

People with breakthrough cases may experience only asymptomatic infection or mild illness, but they can pass the virus to unvaccinated people, who could fall more severely ill, and become a source of new variants.

Dr. Seth Berkley, CEO of Gavi, the global vaccine alliance, said that more data was needed before drawing conclusions about vaccines’ effectiveness against omicron — and that accelerated vaccination should continue to be the focus of pandemic response.

Preliminary data from South Africa suggest that with omicron, there is a much higher chance of people who already had COVID getting reinfected than there was with the original virus and previous variants. But some public health experts say they believe that countries that have already been through brutal waves of COVID, such as Brazil and India, may have a buffer against omicron, and vaccination after infection produces high antibody levels.

“The combination of vaccination and exposure to the virus seems to be stronger than only having the vaccine,” said Ramanan Laxminarayan, a public health researcher. India, he noted, has an adult vaccination rate of only about 40% but 90% exposure to the virus in some areas.

“Without a doubt omicron is going to flood through India,” he said. “But hopefully India is protected to some extent because of vaccination and exposure.”

China does not have this layer of protection to back up its weak vaccines. Because of China’s aggressive efforts to stop spread of the virus within its borders, relatively few people have previous exposure. Only an estimated 7% of people in Wuhan, where the pandemic began, were infected.

Much of Latin America has relied on the Chinese and Russian vaccines, and on AstraZeneca. Mario Rosemblatt, a professor of immunology at the University of Chile, said that more than 90% of Chileans had had two doses of one vaccine, but the great majority of these were Coronavac, the Sinovac shot. High vaccination coverage combined with early reports that omicron does not cause serious illness is leading to a false sense of security in the country, he said.

“We have to get people to understand that it doesn’t work like that: If you get high transmissibility you’re going to have the health system saturated because the number of people getting ill will be higher,” he said.

Laxminarayan said the Indian government, to which he is an occasional adviser, was considering booster shots, but the delta variant still poses a significant threat in India, and two vaccine doses offers protection against delta. That presents the government with a difficult choice between focusing on getting people who remain unvaccinated, or only partly vaccinated, to two doses, or trying to get boosters to older people and those with high-risk medical conditions as protection against omicron.

The news that the non-mRNA vaccines offer little protection against infection from omicron may further erode demand for shots in countries already struggling to build demand, Morrison said.

“This challenges the whole value of vaccines,” he said. “If you’re so far behind and then you suffer this, it’s going to feed anti-vaccine sentiment and weaken confidence.”