Why vaccinate people who have had Covid?

Vaccinating people who have had covid-19: why doesn’t natural immunity count in the US?
[BMJ feature.] The substantial number of infections, coupled with the increasing scientific evidence that natural immunity was durable, led some medical observers to ask why natural immunity didn’t seem to be factored into decisions about prioritising vaccination. “The CDC could say [to people who had recovered], very well grounded in excellent data, that you should wait 8 months,” Monica Gandhi, an infectious disease specialist at University of California San Francisco, told Medpage Today in January. “Many of us were saying let’s use [the vaccine] to save lives, not to vaccinate people already immune,” says Marty Makary, a professor of health policy and management at Johns Hopkins University. Real world data have also been supportive. Several studies (in Qatar, England, Israel, and the US) have found infection rates at equally low levels among people who are fully vaccinated and those who have previously had covid-19. But as the delta variant and rising case counts have the US on edge, renewed vaccination incentives and mandates apply regardless of infection history.

Prevention of host-to-host transmission by SARS-CoV-2 vaccines
Here we discuss the available data on the existing, approved SARS-CoV-2 vaccines' capacity to reduce transmissibility by reducing primary infection, viral replication, capacity for transmission, and symptomaticity. The potential for mucosal-targeted SARS-CoV-2 vaccine strategies to more effectively limit transmission than intramuscular vaccines is considered with regard to known immunological mechanisms. Finally, we enumerate the population-level effects of approved vaccines on transmission through observational studies following clinical trials and vaccine distribution in real-world settings.

Real-World Effectiveness of the mRNA-1273 Vaccine Against COVID-19: Interim Results from a Prospective Observational Cohort Study
[Preprint.] This analysis included 352,878 recipients of 2 doses of mRNA-1273 matched to 352,878 unvaccinated individuals. Vaccine effectiveness (VE) (99·3% CI) against COVID-19 diagnosis was 87·4% (84·8-89·6%). VE against COVID-19 hospitalization and hospital death was 95·8% (90·7-98·1%) and 97·9% (66·9-99·9%), respectively. VE was higher against symptomatic (88·3% [98·3% CI: 86·1%-90·2%]) than asymptomatic COVID-19 (72·7% [53·4%-84·0%]), but was generally similar across age, sex, and racial/ethnic subgroups. VE among individuals with history of COVID-19 ranged from 8·2-33·6%. These interim results provide reassuring evidence of the VE of 2 doses of mRNA-1273 across age, sex, and racial/ethnic subgroups, and against asymptomatic and symptomatic COVID-19, and severe COVID-19 outcomes. Among individuals with history of COVID-19, mRNA-1273 vaccination may offer added protection beyond immunity acquired from prior infection.

Ineffective neutralization of the SARS-CoV-2 Mu variant by convalescent and vaccine sera
[Preprint.] Here, we demonstrate that the Mu variant is highly resistant to sera from COVID-19 convalescents and BNT162b2-vaccinated individuals. Direct comparison of different SARS-CoV-2 spike proteins revealed that Mu spike is more resistant to serum-mediated neutralization than all other currently recognized variants of interest (VOI) and concern (VOC). This includes the Beta variant (B.1.351) that has been suggested to represent the most resistant variant to convalescent and vaccinated sera to date. Our results will help to better assess the risk posed by the Mu variant for vaccinated, previously infected and naïve populations.

Emerging SARS-CoV-2 variants of concern evade humoral immune responses from infection and vaccination
We assessed the recognition of three VOCs (B.1.1.7, B.1.351, and P.1) in cohorts of COVID-19 convalescent patients (n = 69) and Pfizer-BioNTech vaccine recipients (n = 50). Spike binding and neutralization against all three VOCs were substantially reduced in most individuals, with the largest four- to sevenfold reduction in neutralization being observed against B.1.351. While hospitalized patients with COVID-19 and vaccinees maintained sufficient neutralizing titers against all three VOCs, 39% of nonhospitalized patients exhibited no detectable neutralization against B.1.351. Moreover, monoclonal neutralizing antibodies show sharp reductions in their binding kinetics and neutralizing potential to B.1.351 and P.1 but not to B.1.1.7. These data have implications for the degree to which pre-existing immunity can protect against subsequent infection with VOCs and informs policy makers of susceptibility to globally circulating SARS-CoV-2 VOCs.