Ten months ago, the results of large clinical trials seemed almost too good to be true: Two messenger RNA vaccines reduced symptomatic cases of Covid-19 by more than 90% in nearly every group that received them.
Now subtle differences emerge over time between the Pfizer Inc.-BioNTech SE and Moderna Inc. vaccines between patient groups. A small US study found declining levels of antibodies with Pfizer’s vaccine, especially in an older group of people. And a larger study from Belgium found that Moderna’s injection can generate more antibodies than Pfizer’s.
But what all this means in the real world is still unclear. While billions of doses of vaccine have been administered around the world, researchers are still working to understand the nuances of how long their protection lasts and how it varies from person to person.
Getting answers to those questions is a critical step in determining who needs a booster shot, especially for the elderly and those with weakened immune systems. The more contagious delta variant, whose emergence has coincided with a slight decline in vaccine effectiveness, has raised the stakes and has led governments to begin rolling out a third dose of the injections. The Food and Drug Administration will hear public arguments on Sept. 17 about whether or not to continue with booster shots of Pfizer’s vaccine.
Much attention has been paid to levels of antibodies, which serve as one of the immune system’s first defense mechanisms. One theory about Moderna’s vaccine is that it makes more of those antibodies because it uses a larger dose and the two doses are delivered over a week-longer period than Pfizer’s.
But antibodies are only one part of immunity and it’s not clear if they’re the most important, especially in the long run.
“Do we know of an antibody level that protects against Covid? The simple answer is we still don’t know,” Moderna chief medical officer Paul Burton said in a conversation with reporters on Friday. Still, Moderna’s research data shows that a third injection six months after the second raises antibody levels “well in that comfort zone” above the levels seen in the first Phase 3 study.
Along with short-term antibodies, Covid vaccines also activate what is essentially long-term memory in the immune system. That memory seems to increase and get better at making variant-fighting antibodies over time. This longer-term protection, including so-called T cells and memory B cells, is more difficult to measure in the laboratory than antibodies. But it is thought to play an important role in preventing serious illness and hospitalizations.
But less than a year into the vaccine campaign, much of the research has focused on vaccine-derived antibodies, which help trap an invading pathogen and mark it for attack by the rest of the immune system.
A small US study examined a group of nursing home patients and staff who received two doses of the Pfizer vaccine. It found that antibody levels in both groups decreased over time. But the 120 residents in the study, with a median age of 76, started out with much lower levels of antibodies than the younger staff.
Over several months, “they end up in an even worse place,” said David Canaday, an infectious disease physician and professor of medicine at Case Western Reserve University in Cleveland, Ohio, who led the study, which was released as a preprint for publication at the end of August.
Two weeks after a second inoculation, neutralizing antibodies had fallen below detection level in 16% of nursing home residents who had not had Covid before their vaccinations. Six months after vaccination, 70% had extremely low levels. In contrast, only 16% of 64 younger caregivers had such lean antibodies after six months, the study found.
“Certainly, the protection will diminish quite a bit with these levels of antibody loss,” Canaday said. But such a loss is unlikely to mean zero protection.
A second study compared antibody levels in 167 University of Virginia health system employees immunized with the Moderna or Pfizer vaccine. Antibody levels after the second vaccine were about 50% higher in people who received the Moderna injection, the researchers said in a letter to Jama Network Open Thursday.
But when the researchers dug further, they found the difference was largely explained by an inferior response to the Pfizer vaccine in people 50 and older, said Jeffrey Wilson, an immunologist at the University of Virginia and co-author of the study. . With the Moderna vaccine, the antibody response after two injections did not differ dramatically by age group.
“There are probably subtle differences between Pfizer and Moderna,” Wilson says. “Whether that has a clinically meaningful impact on protection against the virus remains to be seen.”
The finding from the University of Virginia is broadly consistent with a larger study of more than 1,600 workers at a hospital in Belgium, which found that people who received the Moderna vaccine had, on average, double the antibody level of those who received Pfizer. But the Belgian study, published Monday in the Journal of the American Medical Association, found that Moderna produced higher antibody levels in all age groups.
None of the studies measured whether fewer antibodies lead to less protection over time. But as the delta variant has gained the upper hand, emerging data increasingly show a deteriorating level of protection against immunizations, leading to more reports of breakthrough infections in which a vaccinated person becomes ill.
Protection against serious illness and hospitalization – the main public health benefit of vaccination – has generally remained strong.
“We don’t see the hospitals filling up with vaccinated people,” said Angela Rasmussen, a virologist with the Vaccine and Infectious Disease Organization at the University of Saskatchewan in Saskatoon. “What we’re seeing is mostly unvaccinated people who still make up the bulk of new cases.”
(This story was not edited by NewsMadura staff and was generated automatically from a syndicated feed.)