Oxford: Initial laboratory studies using “live” omicron virus isolated from a patient confirm the suspicion that the new variant of SARS-CoV-2 largely circumvents the immunological protection provided by dual vaccination with AZD1222 or BNT162b2. The results were in medRxiv (2021; DOI: 10.1101/2021.12.10.21267534) published.

The omicron variant is spreading faster than the delta variant this summer and the alpha variant last winter. In the UK there were 4,713 confirmed cases and a first death. The Health Authority UKHSA however, he estimates the real number to be around 200,000 new infections every day. In London, Omicron already accounts for more than 44% of cases and will overtake Delta there in a matter of days.

The reason for the rapid spread is suspected to be the numerous mutations clustered around the receptor-binding motif with which the virus attaches to the ACE2 receptor. This could explain the increased portability. However, the total of 30 amino acid sequence changes plus deletions and an insertion in the spike gene could also mean that antibodies generated by previous infections or vaccinations are ineffective. Without this immune evasion, the rapid spread in South Africa, where 60-80% of the population is predominantly seropositive from previous infections, and now in the UK, where 70% are fully vaccinated, would be inconceivable.

Over the weekend, a test-negative case-control study had already shown that the protective effect after 2 doses of BNT162b2 is low. After 2 doses of AZD1222 it was completely absent. Now, a team led by Matthew Snape of the University of Oxford provides the explanation. The researchers carried out neutralization tests on the omicron variant isolated from an infected person in the UK.

The trial examined whether sera from vaccinees could prevent Omikron from infecting and destroying cell cultures. Sera were from 22 subjects who had received their second dose of AZD1222 4 weeks earlier. Another 21 people had received their second dose of BNT162b2 4 weeks ago. At this point, the antibody concentrations have reached approximately their maximum and the sera must prevent the cells from being killed by the omicrons in the tests.

With the BNT162b2, this was the case only to a limited extent. The median neutralizing antibody titer had fallen from 1,609 in the Victoria strain (which is generally wild-type) to 54 in the omicron variant. The titer fell below the detection limit in 1 participant. For AZD1222, the titer was below the detection limit in all but one participant.

The study shows that there is indeed significant immune evasion through omicrons. Hopes now rest on a push that could restore partial protection. According to Snape, a reliable effect would only be achieved with a special vaccine against Omicron.

Due to numerous changes, this may no longer be effective against other variants. Therefore, it should be considered, according to Snape, to replace the current monovalent vaccine with polyvalent ones. © rme / aerzteblatt.de