Rotavirus vaccine(Sinovac)

Severe acute respiratory syndrome-coronavirus 2 and its variants are still a concern for the World. The effectiveness of the BioNTech and Sinovac vaccines against the B.1.617.2 variant, particularly in the intensive care unit, has been unclear. This study aimed to investigate the vaccine effectiveness of BioNTech and Sinovac vaccines in reducing severe disease, intubation, and mortality rates in B.1.617.2 infected patients followed in the intensive care unit. The data of 208 unvaccinated and 234 vaccinated B.1.617.2 variants were retrospectively reviewed. Severe disease status, complaints, the percent oxygen saturation in the blood at the first admission, and other clinical information during follow-up were recorded. With the BioNTech and Sinovac vaccines being the most common in the region, mortality rate, severe disease, and intubation were more frequent in the unvaccinated group. As for survival rates, 58.5 (137) of the vaccinated and 35.1 % (73) of the unvaccinated survived. In the vaccinated group, 64.3 % (27) of vaccinated with 3 Sinovac, 80 % (16) of 2 Sinovac and 1 BioNTech, and 71.7 % of 2 BioNTech survived. Vaccination with 2 doses of BioNTech and 3 doses of Sinovac reduces mortality. Furthermore, 2 doses of Sinovac and 1 dose of BioNTech are more protective.

In 2022, SARS-CoV-2 Omicron variants circulated globally, generating concerns about increased transmissibility and immune escape. Hong Kong, having an infection-naive population with a moderate 2-dose vaccine coverage (63% by the end of 2021), experienced a COVID-19 epidemic largely seeded by Omicron BA.2 variants that led to the greatest outbreak in the region to date. Little remains known about the protection of commonly-administered vaccines against transmission of Omicron BA.2 variants.

In this retrospective cohort study, we identified 17 535 laboratory-confirmed COVID-19 cases using contact tracing information during the Omicron-predominant period between January and June 2022 in Hong Kong. Demographic characteristics, time from positive test result to case reporting, isolation, or hospital admission, as well as contact tracing history and contact setting were extracted. Transmission pairs were reconstructed through suspected epidemiological links according to contact tracing history, and the number of secondary cases was determined for each index case as a measurement for risk of transmission. The effectiveness of mRNA vaccine (BNT162b2) and inactivated vaccine (Sinovac) against transmission of BA.2 variants was estimated using zero-inflated negative binomial regression models.

Vaccine effectiveness against transmission for patients who received the 2-dose BNT162b2 vaccine was estimated at 56.2% (95% CI: 14.5, 77.6), 30.6% (95% CI: 13.0, 44.6), and 21.3% (95% CI: 2.9, 36.2) on 15 - 90, 91 - 180, and 181 - 270 days after vaccination, respectively, showing a significant decrease over time. For 3-dose vaccines, vaccine effectiveness estimates were 41.0% (95% CI: 11.3, 60.7) and 41.9% (95% CI: 6.1, 64.0) on 15 - 180 days after booster doses of Sinovac and BNT162b2, respectively. Although significant vaccine effectiveness was detected in household settings, no evidence of such protective association was detected in non-household settings for either Sinovac or BNT162b2.

Moderate and significant protection against Omicron BA.2 variants' transmission was found for 2 and 3 doses of Sinovac or BNT162b2 vaccines. Although protection by 2-dose BNT162b2 may evidently wane with time, protection could be restored by the booster dose. Here, we highlight the importance of continuously evaluating vaccine effectiveness against transmission for emerging SARS-CoV-2 variants.