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A registered nurse administers a dose of the Moderna Covid-19 vaccine on April 17, in Gardena, California.
A registered nurse administers a dose of the Moderna Covid-19 vaccine on April 17, in Gardena, California. Patrick T. Fallon/AFP/Getty Images

People who have recovered from coronavirus infections get a big boost of extra immunity from one dose of Pfizer’s vaccine, British researchers reported Friday.

The extra boost comes from immune cells that don’t develop at the same rate after natural infection — and it gives good protection against some of the worrying variants circulating, the researchers reported in the journal Science.

People who have not been infected need both doses of the vaccine to see the same boost, they found.

The team led by Dr. Rosemary Boyton of Imperial College London analyzed blood samples from health care workers at various stages. Some had been infected with coronavirus and recovered, while others had not.

The team looked for both antibodies and immune calls called T cells, which attack invaders, and B cells, which help produce new antibodies over time. They checked these immune responses after vaccination, and tested their blood samples against variants of the virus such as B.1.1.7, first seen in Britain, and B.1.351, first seen in South Africa.

These variants have worrying mutations in the virus’s spike protein, used to enter the cells it infects. B.1.351, especially, evades the human immune response and appears also to evade some of the immune response elicited by vaccines.

“After one dose, individuals with prior infection showed enhanced T cell immunity, antibody secreting memory B cell response to spike and neutralizing antibodies effective against B.1.1.7 and B.1.351,” the team wrote. They found 96% of their volunteers who had been infected already produced T cells that homed in on the virus after getting one dose of vaccine, compared to 70% of people who had not been infected and who had received just one dose of vaccine.

“By comparison, healthcare workers receiving one vaccine dose without prior infection showed reduced immunity against variants,” they said. Each person’s individual genetic makeup affected this response, they found.

Adding a second dose of vaccine to people who had been infected did not add to the immune response. Two doses have been found to greatly boost the immune response of people who have not had coronavirus. The team said their research supported the argument that coronavirus survivors only need one dose of vaccine to enjoy full immunity.