Dynamic IgG seropositivity after rollout of CoronaVac and BNT162b2 COVID-19 vaccines in Chile: a sentinel surveillance study

Abstract

Background By July 14, 2021, 81•3 % of adults (aged ≥18 years) in Chile had received a first SARS-CoV-2 vaccine and 72•3% had received a second SARS-CoV-2 vaccine, with the majority of people given Sinovac's inactivated CoronaVac vaccine (75•3% of vaccines dispensed) or Pfizer-BioNTech's mRNA BNT162b2 vaccine (20•9% of vaccines dispensed). Due to the absence of simultaneous real-world data for these vaccines, we aimed to compare SARS-CoV-2 IgG positivity between vaccines using a dynamic national monitoring strategy. Methods From March 12, 2021, 28 testing stations for SARS-CoV-2 IgG detection were installed in hotspots based on cellular-phone mobility tracking within the most populated cities in Chile. Individuals voluntarily approaching the testing stations were invited to do a lateral flow test by finger prick and respond to a questionnaire on sociodemographic characteristics, vaccination status (including type of vaccine if one was received), variables associated with SARS-CoV-2 exposure, and comorbidities. We compared the proportion of individuals testing positive for anti-SARS-CoV-2 IgG across sites by week since vaccination between recipients of CoronaVac and BNT162b2. Unvaccinated participants served as a control population and were matched to vaccinated individuals on the basis of date of presentation to the testing station, gender, and age group. Individuals were excluded from the analysis if they were younger than 18 years, had no declared gender, had an invalid IgG test result, had previously tested positive for SARS-CoV-2 infection on PCR, could not recall their vaccination status, or had been immunised against COVID-19 with vaccines other than CoronaVac or BNT162b2. Here, we report data collected up to July 2, 2021. Findings Of 64 813 individuals enrolled, 56 261 were included in the final analysis, of whom 33 533 (59•6%) had received at least one dose of the CoronaVac vaccine, 8947 (15•9%) had received at least one dose of the BNT162b2 vaccine, and 13 781 (24•5%) had not received a vaccine. SARS-CoV-2 IgG positivity during week 4 after the first dose of CoronaVac was 28•1% (95% CI 25•0-31•2; 220 of 783 individuals), reaching a peak of 77•4% (75•5-79•3; 1473 of 1902 individuals) during week 3 after the second dose. SARS-CoV-2 IgG positivity during week 4 after the first dose of the BNT162b2 vaccine was 79•4% (75•7-83•1; 367 of 462 individuals), increasing to 96•5% (94•9-98•1; 497 of 515 individuals) during week 3 after the second dose and remaining above 92% until the end of the study. For unvaccinated individuals, IgG seropositivity ranged from 6•0% (4•4-7•6; 49 of 810 individuals) to 18•7% (12•5-24•9; 28 of 150 individuals) during the 5 month period. Regression analyses showed that IgG seropositivity was significantly lower in men than women and in people with diabetes or chronic diseases for CoronaVac vaccine recipients (p<0•0001), and for individuals aged 60 years and older compared with people aged 18-39 years for both vaccines (p<0•0001), 3-16 weeks after the second dose.Interpretation IgG sero...

Serum anti-Spike antibody titers before and after heterologous booster with mRNA-1273 SARS-CoV-2 vaccine following two doses of inactivated whole-virus CoronaVac vaccine

“…Higher pre-boost IgG levels were associated with documented previous SARS-CoV-2 infection, and, unexpectedly, a longer interval since the second vaccine dose. However, when we assessed time since the most recent documented “virus exposure” (either by vaccine or infection), the pre-boost IgG titers correlated negatively, as expected 19–21 . These findings, coupled with the high rate of documented post-CoronaVac virus breakthroughs, confirm intense SARS-CoV-2 exposure among front line heath care workers during the Delta surge in July 2021 25 .…”

“…Real-world data from Chile reported high prevention of hospitalisation (87.5%), ICU admission (90.3%), and COVID-19-related death (86.3%) 16 . However, recent studies reported CoronaVac to have lower immunogenicity than virus vector or mRNA vaccines 18,19 , and a pronounced decrease of neutralising antibody titres within a few months 19–21 , and reduced effectiveness in the elderly 22,23 . This lack of protection is concerning, especially given the rapid emergence of Omicron 6 .…”

SARS-CoV-2 epidemic in the South American Southern cone: can combined immunity from vaccination and infection prevent the spread of Gamma and Lambda variants while easing restrictions?

“…In order to estimate the proportion of immune individuals around the decoupling time, we summed the estimated number of vaccine-immunized and natural-immunized individuals. The proportion of vaccine-immunized individuals was estimated from the number of fully vaccinated individuals adjusted by the estimated vaccine effectiveness (VE) in South America [17,18], see also [19]. The number of infected people that acquired immunity through previous infection (cumulative infection) was estimated from the cumulative number of deaths assuming a constant (age adjusted) infection fatality rate (IFR) for each country (see subsection 4.1 and Table 1).…”

Booster doses for inactivated COVID-19 vaccines: if, when, and for whom

“…Only one study using an mRNA vaccine shows preliminary results: a 95·6% efficacy of mRNA vaccine booster after 5 months. 7 Because of the pronounced decrease of NAbs titres 2 , 6 , 8 and reduced effectiveness in the older population, 9 WHO's Strategic Advisory Group of Experts on Immunization recommend a third dose of inactivated virus vaccines or a heterologous booster for people aged 60 years and older who already have received the two-dose scheme. 10…”