COVID-19 Update - Omicron primer - what we know so far
Key takeaways
- We still have limited data and all estimates and conclusions are subject to changes, as more data and studies are available. Most studies are preprints and not peer-reviewed yet.
- Higher risk of re-infections and breakthrough cases because of omicron, as e.g. vaccine effectiveness against infection is much lower compared to delta. Household transmission is higher for omicron compared to delta. Non-household secondary attack rates are very similar for omicron compared to delta.
- Vaccine efficacy against symptomatic disease after two vaccine doses declines significantly for omicron compared to delta. Effectiveness is restored after the booster. We still do not know for how long protection lasts but a German study suggests protection against omicron wanes after three months, just like after the two first doses against delta.
- Still relatively high vaccine efficacy against hospitalisation after two doses of mRNA. Likely higher after the third jab. Most likely also high for previously infected.
- Many of the new treatments (Pfizer's Paxlovid, Merck's Molnupiravir and GSK's Xevudy) remain effective against omicron. Effectiveness of most current monoclonal antibodies is reduced significantly.
- It is too early to conclude that omicron is a milder variant in itself. The reason for mild-to-moderate cases may simply be due to high immunity degrees across countries where omicron is/about to become dominating. One explanation why it may spread faster but is milder is that it infects human bronchus faster than in the lung.
- Lower micro/individual risk may still lead to worse outcomes from a macro perspective. If the waves become big enough more people may be admitted to hospitals despite a weaker relationship between new cases and hospitalisations.
Key questions going forward
- How fast will omicron spread? Will the daily growth rate start to decline after the very rapid spreading in the early stage?
- Is omicron milder or are lower hospitalisations due to a higher degree of immunity from vaccines and/or infections?
- Vaccine efficacy waned quickly after two doses of Pfizer or Moderna. Is the third dose more long-lasting?
- Will countries start using updated vaccines against omicron once ready? And when are they ready?
