Reinfection, Vaccination, and Post-Recovery Shots

Reinfection. It seems to be on everyone’s mind right now and in our third year of the COVID-19 pandemic, it’s increasingly hard to avoid infection with SARS-CoV-2. For a substantial period in time, we felt well protected with the 90-day window following an acute infection.

The Centers for Disease Control and Prevention (CDC) even states that if you are within 90 days of a recent COVID infection and are exposed again, you don’t need to quarantine if you don’t develop symptoms, meaning that the agency believes the risk for reinfection is quite low during this time frame. More recently though, we’ve been seeing a shortening window of infection-induced protection, in which reinfection with COVID-19 and subvariants like BA.4 and BA.5 is much more common and possible in as little as 30 days.

What happens though, if you recover from COVID-19 and get vaccinated? Boosted? How are your odds against reinfection impacted? A recent article published in JAMA Infectious Diseases, sought to address these nuances and determine how effective vaccination is after COVID-19 recovery in terms of protecting against reinfection. The researchers assessed a nearly 100,000 person cohort of Rhode Island residents between March 2020 to December 2021 within long-term care facilities. While this was pre-Omicron, where reinfection was less likely, this nonetheless amplifies the need for more studies along these lines. The authors noted that completion of the primary vaccine series (e.g. two doses of a two-dose vaccine) after recovery from COVID-19 was associated with a 49% protection from reinfection in residents, but also a 47% protection in employees. In terms of the general population, they saw a 62% protection in the general population during this time period in which variants Alpha and Delta were the most prominent.

The authors breakdown their findings further, noting that “ 3124 LTCC residents (median [IQR] age, 81 [71-89]; 1675 [53.6%] females), 2877 LTCC employees (median [IQR] age, 41 [30-53]; 2186 [76.0%] females), and 94 516 members of the general population (median [IQR] age, 35 [24-52] years; 45 030 [47.6%] females) met eligibility criteria. Probability of reinfection at 9 months for those who remained unvaccinated after recovery from prior COVID-19 was 13.0% (95% CI, 12.0%-14.0%) among LTCC residents, 10.0% (95% CI, 8.8%-11.5%) among LTCC employees, and 1.9% (95% CI, 1.8%-2.0%) among the general population.”

Overall, this study emphasizes the efficacy of vaccines in protecting against reinfection when the full series is completed, and definitely after recovering from an infection. These findings are important in understanding immune protection and defense against COVID-19, but a bit outdated given that neither Delta or Alpha are really in circulation anymore. The overall focus of this study though is important and should be performed against with Omicron and the subvariants like BA.4 and BA.5, but also with the added need for boosters to stay up-to-date. Understanding immunity, but vaccine, but also infection-induced, and a hybrid of the two is increasingly important as non-pharmaceutical interventions are increasingly dropped by public health agencies like the CDC.