BACKGROUND

We investigated the effect of preexisting antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and seasonal human coronaviruses (hCoVs) on infection outcomes in Omicron BA.1/BA.2-exposed household members from January to March 2022.

METHODS

Data from a prospective household study in the Netherlands were used including 63 households with 195 household members exposed to a SARS-CoV-2 Omicron BA.1/BA.2 index case. The protocol included repeated nose-throat swab and saliva reverse-transcription polymerase chain reaction (RT-PCR) testing, paired serology, and self-reported daily symptom scoring by household members. Infection outcomes included the occurrence of secondary infections, symptom burden, and cycle threshold (Ct) value trajectories. We studied the effect of baseline binding antibody levels for SARS-CoV-2 and seasonal hCoVs NL63, 229E, HKU1, and OC43 spike protein, on SARS-CoV-2 infection outcomes.

RESULTS

One hundred thirty-two of 195 (68%) exposed household members developed a SARS-CoV-2 infection. Among exposed household members, higher levels of SARS-CoV-2 at baseline were associated with a reduced risk of secondary infection (adjusted odds ratio, 0.73 [95% confidence interval, .55-.99]). No significant differences between antibody levels and symptom burden or Ct value trajectories were observed.

CONCLUSIONS

Our study suggests that prior SARS-CoV-2 antibodies provide some protection against Omicron BA.1/BA.2 infection, while effects on symptom burden or Ct value could not be demonstrated. The results highlight the relatively limited, but not negligible role of cross-protective antibodies, especially when facing immune escape variants of SARS-CoV-2.