COVID-19 survivors might only need one shot of the new vaccines from Moderna Inc and Pfizer/BioNTech, instead of the usual two doses, because their immune systems have gotten a head start on learning to recognize the virus, according to two separate reports posted this week on medRxiv ahead of peer review.

In one study of 59 healthcare workers who recovered from COVID-19 and received one of the vaccines, antibody levels after the first shot were higher than levels usually seen after two doses in people without a history of COVID-19.

In a separate study, researchers found that 41 COVID-19 survivors developed "high antibody titers within days of vaccination," and those levels were 10 to 20 times higher than in uninfected, unvaccinated volunteers after just one vaccine dose.

"The antibody response to the first vaccine dose in individuals with pre-existing immunity is equal to or even exceeds" levels found in uninfected individuals after the second vaccine dose, the authors of that paper said.

"Changing the policy to give these individuals only one dose of vaccine would not negatively impact on their antibody titers, spare them from unnecessary pain and free up many urgently needed vaccine doses," they said.