Cases surge in Chile despite high vaccination and lockdown
Chile has one of the world’s best vaccination rates. Covid is surging there anyway
[Media report.] Almost 40% of the South American country’s total population have now received at least one dose of a Covid-19 vaccine. Nonetheless, Chile has endured a sharp uptick in coronavirus infections in recent weeks, even with its world-renowned vaccine rollout and strict lockdowns in place for much of its 19 million inhabitants.
Vaccines: Coronavac reduces mortality by 97%, Pfizer by 80%
[Media report.] The Chinese vaccine Coronavac against COVID-19 reduces the mortality of the disease by 97%, while American Pfizer has an 80% effect, according to preliminary results of a study published in Uruguay on Thursday.
Immunological memory and neutralizing activity to a single dose of COVID-19 vaccine in previously infected individuals
Healthcare workers (n = 280) were enrolled after obtaining written informed consent and grouped under previously infected (RT-PCR positive) and no prior exposure group (RT-PCR negative). Blood was drawn at baseline and post vaccination (single dose of COVISHIELD). A higher antibody response (1124.73 ± 869.13 vs94.23 ± 140.06 AU/ml; p = 0.0001), CD4 memory T-cells; central memory CCR7+CD45RA- (p = 0.0001), effector memory CCR7-/CD45RA- (0.01), total CD8+T cells; (p = 0.004), CD8+naïve T cells CCR7+CD45RA+; (p = 0.01) and memory B cells CD20+CD27+; (p = 0.0001) was seen in previously infected individuals with a single dose of vaccine. Single dose vaccination elicited higher neutralizing antibody response and protective immunity in individuals who were previously infected. Hence single dose strategy may be pursued to increase population coverage.
Single-dose BNT162b2 mRNA COVID-19 vaccine significantly boosts neutralizing antibody response in health care workers recovering from asymptomatic or mild natural SARS-CoV-2 infection
Forty-one HCW recovering from mild or asymptomatic infection were evaluated on the day of first-dose vaccination (T1_inf) and 21 days later (T2_inf). Sixteen uninfected HCW were evaluated 20 days after the first dose (T2_uninf) and 20 days after the second dose of vaccine (T3_inf). At T2_inf, but not at T1_inf, there was a significant correlation between days from diagnosis (median [IQR] 313 [285-322]) and NtAb levels (p = 0.011). NtAb titres increased at T2_inf with respect to T1_inf (1544 [732-2232] vs. 26 [10-88]; p < 0.001). Likewise, there was a significant increase in NtAb titres at T3_uninf with respect to T2_uninf (183 [111-301] vs. 5 [5-15]; p < 0001). However, NtAb levels at T2_inf were significantly higher than those at T2_uninf and T3_uninf (p < 0.0001 for both analyses). A single vaccination in people with mild or asymptomatic previous infection further boosts SARS-CoV-2 humoral immunity to levels higher than those obtained by complete two-vaccination in uninfected subjects.
Single-dose SARS-CoV-2 vaccine in a prospective cohort of COVID-19 patients
[Preprint.] We evaluated SARS-CoV-2 specific antibody responses following a single-dose of BNT162b2 (Pfizer-BioNTech) mRNA vaccine in 155 previously SARS-CoV-2-infected individuals participating in a population-based prospective cohort study of COVID-19 patients. Within one week of vaccination, IgG antibody levels to virus spike and RBD proteins increased 27 to 29-fold and neutralizing antibody titers increased 12-fold, exceeding titers of fully vaccinated SARS-CoV-2-naive controls (95% credible interval (CrI): 0.56 to 0.67 v. control 95% CrI: −0.16 to −0.02). Pre-vaccination neutralizing antibody titers had the largest positive mean effect size on titers following vaccination (95% CrI (0.16 to 0.45)). COVID-19 severity, the presence of comorbidities and the time interval between infection and vaccination had no discernible impact on vaccine response. A single dose of BNT162b2 mRNA vaccine up to 15 months after SARS-CoV-2 infection provides neutralizing titers exceeding two vaccine doses in previously uninfected individuals. These findings support wide implementation of a single-dose mRNA vaccine strategy after prior SARS-CoV-2 infection.