COVID-19 vaccines are effective, but
breakthrough infections have been increasingly reported. We conducted a test-negative case-control study to assess the durability of protection against symptomatic
infection after vaccination with
mRNA-1273. We fit conditional logistic regression (CLR) models stratified on residential county and calendar date of SARS-CoV-2 PCR testing to assess the association between the time elapsed since vaccination and the odds of symptomatic
infection, adjusted for several covariates. There were 2,364 symptomatic individuals who had a positive SARS-CoV-2 PCR test after full vaccination with
mRNA-1273 ("cases") and 12,949 symptomatic individuals who contributed 15,087 negative tests after full vaccination ("controls"). The odds of symptomatic
infection were significantly higher 250 days after full vaccination compared to the date of full vaccination (Odds Ratio [OR]: 2.47, 95% confidence interval [CI]: 1.19-5.13). The odds of non-COVID-19 associated hospitalization and non-COVID-19
pneumonia (negative control outcomes) remained relatively stable over the same time interval (Day 250 ORNon-COVID Hospitalization: 0.68, 95% CI: 0.47-1.0; Day 250 ORNon-COVID
Pneumonia: 1.11, 95% CI: 0.24-5.2). The odds of symptomatic
infection remained significantly lower almost 300 days after the first
mRNA-1273 dose as compared to 4 days after the first dose, when immune protection approximates the unvaccinated state (OR: 0.26, 95% CI: 0.17-0.39). Low rates of
COVID-19 associated hospitalization or death in this cohort precluded analyses of these severe outcomes. In summary,
mRNA-1273 robustly protected against symptomatic
SARS-CoV-2 infection at least 8 months after full vaccination, but the degree of protection waned over this time period.