Immunity from natural infection vs vaccination: systematic review
Equivalency of Protection from Natural Immunity in COVID-19 Recovered Versus Fully Vaccinated Persons: A Systematic Review and Pooled Analysis
[Preprint.] Nine clinical studies were identified. Vaccination in COVID-recovered individuals provided modest protection from reinfection (RR=1.82 [95%CI 1.21-2.73], P=0.004), but the absolute risk difference was extremely small (AR= 0.004 person-years [95% CI 0.001-0.007], P=0.02). The number needed to treat to prevent one annual case of infection in COVID-recovered patients was 218, compared to 6.5 in COVID-naïve patients, representing a 33.5-fold difference in benefit between the two populations. While vaccinations are highly effective at protecting against infection and severe COVID-19 disease, our review demonstrates that natural immunity in COVID-recovered individuals is, at least, equivalent to the protection afforded by full vaccination of COVID-naïve populations. There is a modest and incremental relative benefit to vaccination in COVID-recovered individuals; however, the net benefit is marginal on an absolute basis. COVID-recovered individuals represent a distinctly different benefit-risk calculus.
Infections, hospitalisations, and deaths averted via a nationwide vaccination campaign using the Pfizer–BioNTech BNT162b2 mRNA COVID-19 vaccine in Israel: a retrospective surveillance study
In this retrospective surveillance study, we used national surveillance data routinely collected by the Israeli Ministry of Health from the first 112 days (Dec 20, 2020, up to our data cutoff of April 10, 2021) of Israel's vaccination campaign to estimate the averted burden of four outcomes. We estimated that Israel's vaccination campaign averted 158 665 (95% CI 144 640–172 690) SARS-CoV-2 infections, 24 597 (18 942–30 252) hospitalisations, 17 432 (12 770–22 094) severe or critical hospitalisations, and 5532 (3085–7982) deaths. Without the national vaccination campaign, Israel probably would have had triple the number of hospitalisations and deaths compared with what actually occurred during its largest wave of the pandemic to date, and the health-care system might have become overwhelmed.
Seroprevalence of SARS-CoV-2 antibodies and reduced risk of reinfection through six months: a Danish observational cohort study of 44,000 healthcare workers
From April to October 2020 we screened 44,698 healthcare workers (HCW) of which 2,811 were seropositive at least once. The seroprevalence increased from 4.0% (1,501/37,452) to 7.4% (2,022/27,457) during the period (p<0.001). Seropositive HCW had a RR of 0.35 (0.15-0.85, p=0.012) of reinfection during the following six months and 2,115 (95%) out of 2,248 of those who were seropositive during rounds one or two remained seropositive after four to six months. The 133 of 2,248 (5.0%) participants who seroreverted were slightly older and reported fewer symptoms than other seropositive participants. Seropositivity against SARS-CoV-2 persisted for at least six months in the vast majority of HCW and was associated with a significantly lower risk of reinfection.
An Analysis of SARS-CoV-2 Vaccine Breakthrough Infections and Associated Clinical Outcomes
[Preprint.] Using detailed disease investigation data from Washoe County, Nevada we sought to assess the rate of symptomatic infection and serious illness among vaccine breakthrough infections (VBT) cases compared to non-vaccinated individuals with COVID-19. From February 12 - July 29, 2021, the Washoe County Health District identified and traced 6,128 out of 6,399 reported cases across the sample period. 338 (5.5%) of all cases were identified as breakthrough infections, and 289 (86%) vaccinated individuals had symptomatic infections. Severe clinical outcomes were infrequent with 17 hospitalizations (5% of VBT) and no deaths. Cycle threshold values were not statistically different between vaccinated and unvaccinated individuals.
Public Health Measures and the Control of COVID-19 in China
With prompt, vigorous, and coordinated control measures, mainland China contained the spread of the epidemic within two months and halted the epidemic in three months. Aggressive containment strategy, hierarchical management, rational reallocation of resources, efficient contact tracing, and voluntary cooperation of Chinese citizens contributed to the rapid and efficient control of the epidemic, thus promoting the rapid recovery of the Chinese economy. This review summarizes China’s prevention and control strategies and other public health measures, which may provide a reference for the epidemic control in other countries.