New data from a pair of laboratory tests shows that the level of antibodies produced by the combination of the Pfizer/BioNTech and the omicron variant of COVID-19 is significantly reduced. However, those who have received a booster shot may enjoy about the same level of protection against omicron that those with the initial two-shot regime had against delta.

From its first detection, the number of genetic differences found in the omicron variant raised concerns that it would be more evasive of vaccines, as well as of antibodies produced through past infection. That suspicion seemed to be borne out in South Africa, where the number of people getting reinfected after previously being ill with a different variant appears to be much higher than at any point in the past.

That left the question of how much protection is being provided by vaccines. The number of people seeing “breakthrough” infections in South Africa is relatively low, but then, so is the vaccination rate. It was difficult to determine what level of protection is being provided to those who got a jab. Or two. Or three.

Overnight, tests in both South Africa and Germany show that the level of antibody expression against omicron is 37 to 41 times lower than against other variants. Even so, the level of antibodies produced is still high enough to have an impact, and those who have been fully vaccinated—especially those who are a few weeks past receiving a booster—can still expect to see a significant level of protection.

The study from the Africa Health Research Institute delivers a gut-punch right in its title: Omicron incompletely escapes immunity induced by the Pfizer vaccine. In the study, they took live examples of the omicron virus extracted from patients in South Africa, and placed them in incubators with human lung cells. They took blood samples from people who had been fully vaccinated (in the two-shot sense) using the Pfizer/BioNTech vaccine, and samples from people who had been vaccinated after being previously infected by some variant of COVID-19. Adding those blood samples to the combination of virus and lung cells, they looked for the level of antibody response that was generated.

In both cases, they found that the level of antibody production was reduced by orders of magnitude when compared to previous tests. 

The number of people tested was quite small—just 14 samples split between those with no past infection and those with a past infection—but the results were consistent with another small study completed overnight by Pfizer and BioNTech in Germany. The six patients in the study who had been infected were infected in 2020 during the initial wave of cases in South Africa, and not during the delta wave. 

For the patients in the vaccination plus infection group, the response was very strong, indicating that this combination should be highly protective against omicron. Expectations are that people who have received a booster shot should have a reaction on the same level as those who had a past infection plus two-shot regime.

For the patients in the vaccine alone group, the drop in antibody expression was enormous—41 times lower than against past variants. This level of reaction should still provide some level of protection, but much less than what can be expected with a booster, or with the past infection plus vaccine combination.

The full study (as submitted to MedRxiv) also looked into another aspect of omicron: Does it still attach to human cells using only the ACE2 receptor? Genetic analysis suggests that omicron has incorporated sequences of RNA, either from humans or from other coronaviruses, that might allow it to attach to cells at another site. This could help to explain the speed with which omicron has spread within regions of South Africa, as well as making it even more evasive of existing immune responses. 

The results of the study indicate that omicron still attaches to cells only through the ACE2 receptor, attaching using the same spike protein as other variants—though there are multiple changes in that protein.

The Pfizer/BioNTech results backed up the idea that a booster shot gives the vaccine the necessary increase needed to push back against omicron’s evasion. In those results, antibody levels increase 25 times in samples where patients had received a booster. The results were high enough that Pfizer described it this way:

The results of both studies show that people who have had a booster, or those who had full vaccination following a past infection with another COVID-19 variant, are likely to be well protected against omicron—though more real world results are definitely needed. How well protected people are who have had two shots and no booster remains an open question.

In the meantime, statistics and anecdotal reports out of the part of South Africa with the highest level of omicron-related cases continues to generate a level of hope. Despite a surge of cases that’s now been underway for two weeks, there has not been a matching surge in reported deaths. Because COVID-19 patients typically experience weeks of failing health before dying, this isn’t by any means a promise that “omicron is less deadly,” but it remains a hopeful sign. On the other hand, hospitalization levels in the area are up, so omicron is still clearly capable of causing severe illness.