A new study finds in New York that people who know they were infected with SARS-CoV-2 in the past may need only one shot of the Pfizer vaccine to gain strong immunity. Moreover, it is found that in previously infected individuals with positive SARS-CoV-2 spike IgG levels, "the second dose did not significantly increase IgG levels compared with the first dose, suggesting that first dose may be acceptable in this group".

The study, published in the JAMA Network Open, included 29 Chicago-area residents with a prior case of Covid infection based on PCR testing, and another group of 30 people with no such histories. The team evaluated the SARS-CoV-2 spike immunoglobulin G antibody levels after 1 and 2 BNT162b2 doses in previously infected individuals compared with those without previous infection. However, it is important to note that a positive PCR diagnosis alone was not enough to discount the need for a second vaccine dose.

"This study highlights the potential for recommending a single dose for previously infected individuals and may be useful for discussions surrounding vaccination strategy," the researchers said. They also noted the study limitations such as small sample size, diversity of participants (sex, race, nationality), lack of neutralization studies, and lack of T-cell response studies.

Study suggests antibodies produced by a Covid variant neutralise others

Moderna clinical trial: Covid booster shot produced robust response against Delta variant

Scientists identify protein in the blood could be responsible for inflammatory response