As people around the world grapple with the prospect of living with the coronavirus for the foreseeable future, a question arises: how long before they need another vaccine?
Not for months, and possibly years, according to a wave of new studies.
Three doses of a Covid vaccine – or even just two – are enough to protect most people from serious illness and death for a long time, the studies suggest.
“We are now starting to see diminishing returns on the number of additional doses,” said John Wherry, director of the Institute of Immunology at the University of Pennsylvania. Although people over 65 or at high risk of disease may benefit from a fourth dose of the vaccine, it may be unnecessary for most people, he added.
Federal health officials, including Dr. Anthony S. Fauci, the Biden administration’s top Covid adviser, also said they were unlikely to recommend a fourth dose until the fall.
The Omicron variant can dodge antibodies – immune molecules that prevent the virus from infecting cells — produced after two doses of a Covid vaccine. But a third injection of the mRNA vaccines made by Pfizer-BioNTech or by Moderna prompts the body to make a much wider variety of antibodies, which would be difficult to evade any variant of the virus, according to the most recent studyposted on Tuesday.
The diverse repertoire of antibodies produced should be able to protect people against new variants, even those that differ significantly from the original version of the virus, the study suggests.
What’s more, other parts of the immune system can remember and destroy the virus for many months or even years, according to at least four studies published in leading journals in the past month.
Specialized immune cells called T cells produced after immunization by four Covid vaccine brands – Pfizer-BioNTech, Moderna, Johnson & Johnson and Novavax – are about 80% as potent against Omicron as other variants, according to research. Given the difference between the Omicron mutations and previous variants, it is very likely that T cells would mount an equally robust attack against any future variant, the researchers said.
This matches what scientists found for the SARS coronavirus, which killed nearly 800 people in a 2003 outbreak in Asia. In people exposed to this virus, T cells lasted over 17 years old. Evidence so far indicates that the new coronavirus’ immune cells – sometimes called memory cells – may also decline very slowly, experts have said.
“Memory responses can last for centuries,” said Wendy Burgers, an immunologist at the University of Cape Town who led one of the studies, published in the journal Nature. “Potentially, the T-cell response is extremely long-lasting.”
Throughout the pandemic, a disproportionate amount of research attention has been focused on antibodies, the body’s first line of defense against a virus. This is partly because these molecules are relatively easy to study: they can be measured from a drop of blood.
Analyzing immune cells, on the other hand, requires milliliters of blood, skill, specialized equipment – and a lot of time. “It’s orders of magnitude slower and more laborious,” Dr. Burgers said.
Few laboratories have the means to study these cells, and their discoveries are several weeks behind those on antibodies. Perhaps as a result, scientists have often overlooked the importance of other parts of the immune system, experts said.