EVANSTON, IL — A new study published this week finds that two months after inoculation with the Pfizer or Moderna vaccine, antibody response drops by 20% in adults who had a previous COVID-19 infection.
A team of scientists at Northwestern University is hoping their new study will help unlock the mysteries of the COVID vaccine's protection over time.
“This new protocol that we've developed here in this facility is called a surrogate virus neutralization test, and it detects the presence of neutralizing antibodies,” said Thom McDade a biological anthropologist and faculty fellow at the Institute for Policy Research at Northwestern University.
Earlier this year, McDade and his team developed a home antibody test. It focused on these neutralizing antibodies— proteins made by the immune system that disarms the coronavirus.
Testing for these neutralizing antibodies, he says, can help measure how robust of an immune response a person has following an infection.
“Let's say you got COVID. We could measure your antibodies after infection and to see how strong of an antibody response your body mounted to that and have some sense of the level of antibody protection moving forward,” said McDade.
In a 10,000-person study, investigators explored community spread and how much protective immunity has developed.
“We've been focusing more on the level of protection and the response to the vaccine and how that can prevent subsequent waves of infection in the future,” he said.
Researchers say the data underscores the importance of receiving that second dose of vaccine.
“The big takeaways are that the vaccine works. Antibody levels do go down a little bit over time, and that's probably contributing to the breakthrough infections we're seeing,” said McDade. “But those infections are mild and asymptomatic primarily.”
The data also indicated that exposure to COVID-19 doesn't guarantee a high level of antibodies or a robust antibody response after just getting one dose of the two-dose vaccines. It's a strong refutation to the assumption that getting infected with COVID will make someone naturally immune to re-infection.
“Our data says that's not the case. Pretty much everyone needs two full doses, particularly in the context of waning immunity over time and these new variants,” he said.
While the study included testing of emerging variants-- like the ones from South Africa, Brazil and the UK – the newer and more infectious delta variant and the phenomenon of breakthrough cases they say will be part of their next study.
“As people start to get boosters, we'll get some blood samples before and after that so we can monitor the magnitude of that response. But we need to tie that information to infections,” said McDade.
It could provide a better understanding of the intersection between more infectious variants, waning immunity, and the responsiveness of third doses ahead.