GlobalHealth Threats

In the 19 January Morbidity and Mortality Weekly Report (MMWR) from the U.S. Centers for Disease Control and Prevention (CDC), evidence shows that in California and New York between May to November 2021, both COVID-19 vaccination and surviving a prior infection protected individuals against infection and hospitalization from COVID-19.

Four group of adults over the age of 18 years were considered: persons who were

1. unvaccinated with no previous laboratory-confirmed COVID-19 diagnosis,
2. vaccinated (14 days after completion of a primary COVID-19 vaccination series),
3. unvaccinated with a previous COVID-19 diagnosis,
4. vaccinated with a previous COVID-19 diagnosis.

COVID-19 incidence was highest in both California and New York in those who were unvaccinated and did not have prior COVID-19 infection across this entire period. Specifically looking at data in October after the Delta variant became the most prominent variant in the U.S., compared to individuals who were unvaccinated and did not have previous COVID-19 diagnosis, COVID-19 case rates in vaccinated persons without previous COVID-19 diagnosis were 6.2-fold and 4.5-fold lower in California and New York, respectively. Rates were even lower in both groups who had previous COVID-19 infection; in California, COVID-19 case rates were 29.0-fold lower among unvaccinated persons with a previous diagnosis and 32.5-fold lower among vaccination persons with a previous COVID-19 diagnosis; in New York, rates were 14.7-fold lower in those who are unvaccinated but had previous diagnosis, and 19.8-fold lower among those who were vaccinated and had previous COVID-19 diagnosis.