Waning of mRNA-1273 vaccine effectiveness against SARS-CoV-2 infection in Qatar

ABSTRACT

BACKGROUNDIn early 2021, Qatar launched a mass immunization campaign with Modernas mRNA-1273 COVID-19 vaccine. We assessed persistence of real-world mRNA-1273 effectiveness against SARS-CoV-2 infection and against COVID-19 hospitalization and death. METHODSEffectiveness was estimated using test-negative, case-control study design, between January 1 and December 5, 2021. Effectiveness was estimated against documented infection (a PCR-positive swab, regardless symptoms), and against any severe (acute-care hospitalization), critical (ICU hospitalization), or fatal COVID-19. RESULTSBy December 5, 2021, 2,962 breakthrough infections had been recorded among those who received two mRNA-1273 doses. Of these infections, 19 progressed to severe COVID-19 and 4 to critical, but none to fatal disease. mRNA-1273 effectiveness against infection was negligible for the first two weeks after the first dose, increased to 65.5% (95% CI 62.7-68.0%) 14 or more days after the first dose, and reached its peak at about 90% in the first three months after the second dose. Effectiveness declined gradually starting from the fourth month after the second dose and was below 50% by the 7th month after the second dose. Effectiveness against severe, critical, or fatal COVID-19 reached its peak at essentially 100% right after the second dose, and there was no evidence for declining effectiveness over time. Effectiveness against symptomatic versus asymptomatic infection demonstrated the same pattern of waning, but effectiveness against symptomatic infection was consistently higher than that against asymptomatic infection and waned more slowly. CONCLUSIONSmRNA-1273-induced protection against infection appears to wane month by month after the second dose. Meanwhile, protection against hospitalization and death appears robust with no evidence for waning for several months after the second dose.