Understanding Breakthrough Infections Following mRNA SARS-CoV-2 Vaccination

The current surge in infections with the SARS-CoV-2 Delta variant has made it clear to health care workers and the public alike that fully vaccinated people remain at risk for SARS-CoV-2 infections. It is also apparent that breakthrough infections in fully vaccinated people can sometimes be serious. As of October 21, 2021, for example, 35% of the 519 patients hospitalized with COVID-19 in Massachusetts had been fully vaccinated.1 Furthermore, multiple reports have documented that if fully vaccinated individuals do become infected, their viral loads may be as high as the levels seen in unvaccinated individuals.

Coverage and Estimated Effectiveness of mRNA COVID-19 Vaccines Among US Veterans

Question What was the COVID-19 vaccination coverage and estimated mRNA COVID-19 vaccine effectiveness (VE) among US veterans in the first 3 months following vaccine rollout? Findings In this case-control study including 6 647 733 veterans, 23% of veterans received at least 1 COVID-19 vaccination during the first 3 months of vaccine rollout. VE against infection was estimated to be 95% for full vaccination; estimated VE against COVID-19-related hospitalization was 91%, and there were no COVID-19–related deaths among fully vaccinated veterans. Meaning These findings suggest that early vaccination rollout for veterans was efficient, and estimated VE was high for this diverse US population.

Protection of BNT162b2 Vaccine Booster against Covid-19 in Israel

Background: On July 30, 2021, the administration of a third (booster) dose of the BNT162b2 messenger RNA vaccine (Pfizer-BioNTech) was approved in Israel for persons who were 60 years of age or older and who had received a second dose of vaccine at least 5 months earlier. Data are needed regarding the effect of the booster dose on the rate of confirmed coronavirus 2019 disease (Covid-19) and the rate of severe illness. Conclusions: In this study involving participants who were 60 years of age or older and had received two doses of the BNT162b2 vaccine at least 5 months earlier, we found that the rates of confirmed Covid-19 and severe illness were substantially lower among those who received a booster (third) dose of the BNT162b2 vaccine.

Surveillance for Adverse Events After COVID-19 mRNA Vaccination

Question Are mRNA COVID-19 vaccines associated with increased risk for serious health outcomes during days 1 to 21 after vaccination? Findings In this interim analysis of surveillance data from 6.2 million persons who received 11.8 million doses of an mRNA vaccine, event rates for 23 serious health outcomes were not significantly higher for individuals 1 to 21 days after vaccination compared with similar individuals at 22 to 42 days after vaccination.

Variants of SARS-CoV-2

When a virus develops a new mutation, it is called a variant of the original virus. As viruses spread, they constantly change through mutations to their genetic code. Most mutations in the SARS-CoV-2 genome do not affect the functioning of the virus. However, mutations in the spike protein of SARS-CoV-2, which binds to receptors on cells lining the inside of the human nose, may make the virus easier to spread or affect how well vaccines protect people. Other mutations may lead to SARS-CoV-2 being less responsive to treatments for COVID-19.