Omicron threat may be countered with additional dose of Covid-19 vaccine

The earliest studies on Omicron are in and the glimpse they’re providing is cautiously optimistic: while vaccines like the one made by Pfizer Inc and BioNTech SE may be less powerful against the new variant, protection can be fortified with boosters.

Studies from SA and Sweden are showing Omicron does, as feared, cause a loss of immune protection, but not a complete one. In a study of blood plasma from people given two doses of the Pfizer-BioNTech shot, there was a 41-fold drop in levels of virus-blocking antibodies compared with the strain circulating at the start of the pandemic. 

A separate study from Stockholm’s Karolinska Institute was more optimistic, finding the decline in antibodies against Omicron was only slightly worse than for Delta, the strain causing most Covid-19 cases worldwide. 

The loss of immune protection is “robust but not complete”, said Alex Sigal, head of research at the Africa Health Research Institute in Durban, who presented the findings of the first study over Zoom late on Tuesday.

“A good booster probably would decrease your chance of infection, especially infection leading to more severe disease,” he said.

The results of the first reported experiments on the effectiveness of vaccines against Omicron come as governments and financial markets try to gauge if the new variant will have a significant impact on the world’s attempt to move past the pandemic.

Omicron’s rapid spread has raised concern the strain would be sufficiently immune-evasive to require new vaccines, and hundreds of researchers have been working around the clock to answer the question. 

Initial reaction to the study results from some experts was encouraging.

“The Karolinska data is reason for optimism,” said Shane Crotty, a professor in the Centre for Infectious Disease and Vaccine Research at San Diego’s La Jolla Institute for Immunology.

“That is pretty close to the best case scenario I was considering.”

Important weapon

Levels of neutralising antibodies are a key marker of immune protection. Though they naturally decline in the months after an infection or vaccination, their ability to thwart coronavirus variants has been show to improve over time. What’s more, studies have found a third dose six months after the second can bolster levels of these better-quality antibodies, making boosters an important weapon to fight Omicron. 

“There will be more breakthroughs” of vaccine-induced immunity, Sigal said, adding fully vaccinated people should get booster shots and those who’ve been previously infected should get vaccinated. 

Representatives for Pfizer and BioNTech, makers of the first Covid-19 vaccine cleared in the US, didn’t immediately respond to a request for comment. New York-based Pfizer is slated to release its own data today. 

The World Health Organisation (WHO) has that warned Omicron could fuel surges with “severe consequences” amid signs that it makes the coronavirus more transmissible.

The jump in cases in SA after Omicron’s emergence hasn’t overwhelmed hospitals so far, prompting some cautious optimism that the new strain may cause mostly mild illness. 

Preliminary results 

The results are preliminary and exact levels of immune escape may change, said Sigal, whose lab was the first to isolate the Beta variant identified in SA in late 2020. He noted Omicron escapes antibody neutralisation more readily than Beta, which had been considered the most immune evasive of the variants of concern detected previously. 

A key question researchers are trying to address is whether existing Covid-19 vaccines need to be altered to protect against Omicron. 

The Geneva-based WHO is looking to play a co-ordinating role on any such recommendation, as it does with seasonal influenza vaccines, Ana-Maria Henao-Restrepo, who co-leads the WHO’s research and development blueprint for vaccines and innovations during outbreaks and pandemics, said last week. 

Any vaccine changes would require careful consideration, especially since Delta is still the main driver of the pandemic and existing vaccines provide a sufficient shield against it, she said.

More data

The magnitude of the drop in neutralising antibodies against Omicron could indicate a need for Omicron-matched vaccines, though other considerations may play a role, said Stephen Goldstein, an evolutionary virologist at the University of Utah in Salt Lake City.

Larger studies looking at neutralising antibodies from people immunised with other vaccines are also needed, he said.

“More importantly though will be epidemiological studies looking at the frequency of reinfections and breakthrough infections, as well as disease severity in those patients,” Goldstein said.

“I am still optimistic vaccination or prior infection will provide some measure of protection against severe disease.”

Since SA announced the discovery of Omicron on November 25, about 450 researchers globally have been working to isolate the variant from patient specimens, grow it in labs, verify its genomic sequence, and establish methods to test it in blood-plasma samples.

The work in Sigal’s lab involved testing 14 blood plasma samples collected from a dozen people who had been given a second Pfizer-BioNTech shot about a month earlier to gauge the concentration of antibodies needed to neutralise, or block, the live Omicrion virus.

Levels of neutralising antibodies against the variant were significantly higher in a subset of participants who had Covid-19 about a year earlier, Sigal said.

Hybrid immunity

That indicates hybrid immunity, generated by natural infection followed by immunisation, may provide reasonable protection against Omicron. In those who have never had Covid-19, this could be emulated by administering three doses of vaccine, the La Jolla Institute’s Crotty said.

“What many of us want to see is head-to-head comparisons against other variants  because of the broader experience with them,” he said.

Scientists also want to better understand the significance of the reduction in levels of neutralising antibodies against Omicron, and study the antibody responses against Omicron in blood sera from people who have received three doses of either the Pfizer or Moderna vaccines, Crotty said. 

In the weeks ahead, more clarity will also emerge from studies assessing the T cell response to Omicron, including one being run by the La Jolla Institute’s Alessandro Sette. 

It’s possible Omicron will have a less extreme impact on T cells, the white blood cell the immune system uses to kill virus-infected cells, said Dan Barouch, professor of medicine at Harvard Medical School and head of Boston’s Beth Israel Deaconess’ Centre for Virology and Vaccine Research. 

The responses of CD8 or “killer” T cells are likely to be important for protection against severe disease, he said.

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