People looking for a booster shot of a Covid-19 vaccine probably don’t need to worry about which brand it is: Many vaccine combinations can provide strong protection, according to a large new study.
Comparing vaccines from seven different brands, British researchers found that most elicited a strong immune response, with mRNA injections from Moderna and Pfizer-BioNTech eliciting the greatest response. The study was published Thursday in The Lancet.
“This is useful data for policymakers,” said Merry Voysey, a statistician at the University of Oxford who was not involved in the study. “The most important takeaway here is that there are many excellent amplification options for third doses.”
It’s too early for researchers to tell how well different vaccine boosters will work against a new variant of Omicron, which has mutations that could allow it to evade some of the antibodies produced by existing Covid-19 vaccines. Some researchers suspect that humans will need very high levels of antibodies to protect themselves from it.
All 2878 volunteers in the study initially received two vaccines, either AstraZeneca or Pfizer. (Both of these vaccines are licensed in the UK; vaccines from Pfizer, Moderna, and Johnson & Johnson are licensed 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 vaccines that are not permitted anywhere: the mRNA vaccine from CureVac and the Valneva vaccine made from inactivated coronaviruses. Finally, some of the volunteers received a meningitis control vaccine.
Four weeks later, the researchers collected blood samples from the volunteers and measured their antibody levels. They also looked for immune cells known as T cells, which specifically attack other cells infected with the coronavirus.
Antibody and T-lymphocyte levels increased in people who received the Covid-19 booster compared to those who received the meningitis vaccine. However, the range was quite large. The people who got the Valneva booster after the Pfizer vaccine only had 30% more than the control group. But the Moderna booster has increased by at least 1,000 percent.
The new study also showed that boosters increase the number of T-lymphocytes that recognize the coronavirus. Antibodies can neutralize coronavirus well in the early stages of infection, when the virus colonizes the nose. But deep in the airways, T cells can provide a second line of defense.
During the trial, the volunteers did not observe how well the booster vaccines actually prevent 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.
December 2, 2021 5:27 PM ET
Most of the boosters used in the study raised antibody levels to levels equivalent to at least 90 percent protection against infection. And mRNA vaccines from Pfizer and Moderna produced much higher levels of antibodies than other vaccines.
“Whatever you try the first time, I would say, 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.
However, according to other scientists, most of the other vaccines in the study performed well enough for people to feel comfortable getting them too.
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“If your country or region of the world has only one vaccine that we have shown can be effective, it can be used as an enhancer and safely,” said Saul Faust, an infectious disease expert at the University. Southampton and co-author of the study. “It’s not just mRNA.”
John Moore, a virologist at Weill Cornell Medicine in New York who was not involved in the study, said people shouldn’t rely too heavily on the modest differences between most vaccines.
“I don’t consider this a beauty pageant in the sense that one is slightly higher than the other,” he said. “We cannot afford to value this too much.”
Dr. Moore said the new study could give public health officials confidence that they can use a variety of booster vaccines, whichever is most convenient. Novavax and Johnson & Johnson, for example, make vaccines that can be stored in refrigerators, whereas mRNA vaccines must be kept frozen.
An inevitable flaw in the new study was that the researchers did not compare the boosters with the new Omicron variant. Omicron, discovered just last month, has raised serious concerns among researchers due to its many mutations. A booster that is 90 percent effective against the original strain may be worse against Omicron.
How much worse is unknown. Experiments on Omicron have not yet begun because scientists must first figure out how to grow this variant in a laboratory. Dr. Faust and his colleagues have already sent blood samples from volunteers to British government laboratories, where researchers will see how well their boosted antibodies and immune cells work against Omicron. “I think we will start seeing these results in a few weeks,” said Dr. Faust.
If boosters don’t work against this option, vaccine developers will have to get new vaccines, according to Dr. Stanley Plotkin, a vaccine expert and professor emeritus at the University of Pennsylvania. He added that mRNA vaccines could be quickly adapted to target Omicron mutations, or researchers could try a more sophisticated approach: a universal vaccine against any coronavirus.
“Assuming Omicron is eluding antibodies to the original virus and current variants, then we should have a different philosophy,” he said.