Most Covid Vaccines Will Work As Boosters, Study Finds
People looking for a Covid-19 vaccine booster probably don’t need to worry about the brand: Many vaccine combinations are likely to provide strong protection, large new study finds .
In a comparison of seven different vaccine brands, British researchers found that most of them elicited a strong immune response, with mRNA injections from Moderna and Pfizer-BioNTech eliciting the most prominent responses. The study was published Thursday in The Lancet.
“This is welcome data for policy makers,” said Merryn Voysey, a statistician at the University of Oxford who was not involved in the study. “The most important take home message here is that there are a number of great third dose booster options.”
It is too early for researchers to say much about the effectiveness of the various booster shots against the new Omicron variant, which has mutations that could allow it to escape some of the antibodies produced by existing Covid-19 vaccines. Some researchers suspect that people need a very high level of antibodies to protect themselves from them.
All 2,878 study volunteers initially received two injections of AstraZeneca or Pfizer vaccines. (Both of these vaccines are approved in Britain; injections from Pfizer, Moderna, and Johnson & Johnson have been approved in the United States.)
The researchers then tested seven different vaccines as boosters: together with AstraZeneca and Pfizer, they tried three brands that were licensed in different countries: Johnson & Johnson, Moderna and Novavax. They also tried two injections that were not authorized anywhere: an mRNA vaccine from CureVac and a vaccine from Valneva made from inactivated coronaviruses. Finally, some of the volunteers received a meningitis vaccine as a control.
After four weeks, the researchers took blood samples from the volunteers and measured their antibody levels. They also looked for immune cells, called T cells, which specifically attack other cells infected with the coronavirus.
Antibody and T cell levels increased in people who were boosted with Covid-19 compared to those who received the meningitis vaccine. The range was however quite wide. People who received the Valneva booster after a Pfizer vaccine saw only a 30% increase compared to the control group. But a Moderna booster produced at least a 1,000 percent increase.
The new study also found that the boosters increased T cells that recognize the coronavirus. Antibodies can be effective in clearing the coronavirus early in an infection, when the virus colonizes the nose. But deep in the airways, T cells can provide a second line of defense.
The trial did not follow volunteers to see how well the booster shots actually prevented infection or disease. But in recent months, researchers have shown that measuring antibody levels can be a pretty good way to predict the effectiveness of a vaccine.
Most of the boosters used in the study raised antibodies to a level that would equate to at least 90% protection against infection. And the mRNA vaccines from Pfizer and Moderna produced much higher levels of antibodies than other vaccines.
“I would say whatever you got the first time around, having an mRNA booster is probably a good idea,” said Eleanor Riley, an immunologist at the University of Edinburgh who was not involved in the new study.
Yet, according to other scientists, most of the other vaccines in the study gave results that were potent enough that people would feel comfortable receiving them as well.
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“If your country or region of the world has only one of the vaccines that we have shown can boost, it will be good to use as a booster and safe,” said Saul Faust, infectious disease expert at the ‘University. from Southampton and co-author of the study. “It’s not just about mRNA.”
John Moore, a virologist at Weill Cornell Medicine in New York who was not involved in the study, said people shouldn’t take too much advantage of the modest differences between most vaccines.
“I don’t see it as a beauty pageant, in the sense that one is slightly superior to another,” he said. “We can’t afford to be too precious about this.”
Dr Moore said the new study could give public health officials the confidence to turn to different vaccines for boosters, whichever is more practical. Novavax and Johnson & Johnson, for example, make vaccines that can be stored in refrigerators, while mRNA vaccines must be stored frozen.
An inevitable shortcoming of the new study was that the researchers had not measured the boosters against the new Omicron variant. Discovered only last month, Omicron has raised serious concern among researchers due to its numerous mutations. A booster that is 90 percent effective against the original strain could do worse against Omicron.
How much of the worst is unknown. Experiments on Omicron have not started because scientists must first figure out how to grow the variant in the lab. Dr Faust and his colleagues have already sent blood samples from the trial volunteers to UK government labs, where researchers will see how their enhanced antibodies and immune cells work against Omicron. “I think we’ll start to see these results in a few weeks,” Dr. Faust said.
If the boosters don’t work well against the variant, vaccine developers will have to give new injections, said Dr. Stanley Plotkin, vaccine expert and professor emeritus at the University of Pennsylvania. MRNA vaccines could be quickly adapted to target Omicron mutations, he added, or researchers could try a more difficult approach: a universal vaccine against any coronavirus.
“Assuming Omicron escapes the antibodies from the original virus and the current variants, then we have to have a different philosophy,” he said.