The Modern vaccine produces more antibodies than Pfizer. Does it matter?

Ten months ago, the results of large clinical trials seemed far too good to be true: two messenger RNA vaccines reduced symptomatic cases of COVID-19 by more than 90% in almost all groups that obtained them.

Now, over time, subtle differences arise between the Pfizer Inc.-BioNTech SE and Moderna Inc. vaccines. A small American study found declining levels of antibodies with the Pfizer vaccine, particularly in a larger group of people. And a larger study in Belgium found that the Modern shot can generate more antibodies than Pfizer.

But what all this means in the real world is still unclear. Although hundreds of millions of doses of vaccines have been administered worldwide, researchers continue to work to understand the nuances of how long their protection lasts and how it differs from person to person.

Getting answers to these questions is a crucial step in determining who may need a booster shot, especially when it comes to older people and people with weakened immune systems. The most infectious delta variant, the rise of which has coincided with slight declines in vaccine effectiveness, has raised stakes and led governments to begin deploying a third dose of the shots. The U.S. Food and Drug Administration will hear public arguments on Sept. 17 about whether or not to proceed with booster shots of the Pfizer vaccine.

Much of the focus has been on antibody levels, which serve as one of the foremost defenses of the immune system. One theory about Moderna’s vaccine is that it creates more of these antibodies because it uses a larger dose and both doses are given over a one-week period longer than Pfizer’s.

But antibodies are only one component of immunity and it is unclear if they are the most important, especially in the long run.

“Do we know a level of antibodies that protects against COVID? The simple answer is that we don’t know yet, “Paul Burton, Moderna’s chief medical officer, told reporters on Friday. However, data from Moderna’s trial show a third shot six months after the second increases antibody levels “up to this comfort zone” above the levels seen in the initial trial in the final phase.

Immune memory

Along with shorter antibodies, COVID-19 vaccines also trigger what is essentially a long-term memory in the immune system. This memory appears to increase and improve antibody production against the variant over time. This long-term protection, which includes what are known as T cells and memory B cells, is more difficult to measure in the laboratory than antibodies. But it is believed to play an important role in the prevention of serious illnesses and hospitalizations.

But less than a year into the vaccine campaign, much of the research has focused on antibodies derived from the vaccine, which help to target an invasive pathogen and mark it to attack the rest of the system. immune.

A small U.S. study examined a group of patients and nursing home staff who received two doses of the Pfizer vaccine. Antibody levels in both groups were found to decrease over time. But the study’s 120 residents, who had a mean age of 76, started with a much lower level of antibodies than younger staff.

For several months, “they end up in an even worse place,” said David Canaday, an infectious disease doctor and professor of medicine at Case Western Reserve University in Cleveland, Ohio, who led the study, which was published as prepress before publication in late August.

Two weeks after a second inoculation, neutralizing antibodies had fallen below the detection level in 16% of nursing home residents who had not had COVID-19 before their vaccinations. Six months after vaccination, 70% had extremely low levels. In contrast, only 16% of the 64 youngest caregivers had such scarce antibodies for six months, the study found.

“Protection will definitely fall a good amount with these levels of antibody loss,” Canaday said. But this loss is unlikely to mean zero protection.

A second study compared antibody levels in 167 University of Virginia health system officials immunized with the Modern or Pfizer vaccine. Antibody levels after the second vaccine were about 50 percent higher in people who received the Modern shot, researchers said Thursday in a letter to Jama Network Open.

Subtle differences

But when the researchers delved deeper, they found that the difference was mostly explained by a lower response to the Pfizer vaccine in people 50 and older, says Jeffrey Wilson, a University of Virginia immunologist and co-author of the study. With the Modern vaccine, the antibody response after two shots did not differ drastically by age group.

“There are probably subtle differences between Pfizer and Modern,” Wilson said. “It remains to be seen whether this has a clinically significant impact on virus protection.”

The University of Virginia’s finding is generally consistent with a larger study of more than 1,600 workers at a hospital in Belgium that found that people who received the Modern vaccine had, on average, twice the levels of antibodies. of those who received Pfizer. But the Belgian study, published Monday in the Journal of the American Medical Association, found that Moderna produced higher levels of antibodies in all age groups.

None of the studies measured whether fewer antibodies result in less protection over time. But as the delta variant has taken over, emerging data is increasingly showing a deterioration in the level of protection against vaccinations, leading to more reports of advanced infections in which a vaccinated person becomes ill.

Protection against serious illness and hospitalization – the most important health benefit of vaccination – has generally remained strong.

“We’re not seeing hospitals being filled with vaccinated people,” says Angela Rasmussen, a virologist with the University of Saskatchewan’s Vaccine and Infectious Diseases Organization in Saskatoon. “What we’re seeing is that most unvaccinated people continue to make up the majority of new cases.”