In one of the most eagerly awaited studies in recent months, South African scientists have established that Pfizer’s mRNA vaccine alone will not be of much use in preventing or neutralizing the new variant of COVID-19 virus, known as Omicron. The results also suggest that other vaccines — which too target only the spike protein of the virus — are unlikely to fare any better.
There is, however, good news for those who have already got infected with COVID-19, as antibodies from previous infections have been shown to be largely effective in neutralizing or limiting the proliferation of Omicron.
In a statement, the Africa Health Research Institute said their research “strongly suggests that the SARS-CoV-2 Omicron variant escapes antibody immunity induced by the Pfizer-BioNTech (Comirnaty) vaccine, but that considerable immunity is retained in people who were both vaccinated and previously infected.”
The test results are not very surprising, given that nearly all the vaccines today contain only the spike protein of SARS-CoV-2 virus, and not the entire virus.
However, the spike protein of the new variant, Omicron. is heavily mutated (modified) compared to the spike protein of the original virus. This means that antibodies (attack chemicals) produced by the human body against the original spike protein (contained in the vaccine) will not be able to identify and attack the new virus with its modified spike protein.
The latest test has justified the misgivings expressed by Stéphane Bancel, CEO of vaccine maker Moderna, that his scientists had predicted a ‘material drop’ in the effectiveness of current vaccines against the Omnicron variant of SARS-CoV-2 — the virus that causes COVID-19.
INFECTION ANTIBODIES STILL WORK
On the other hand, antibodies and ‘immunity memory’ retained from previous infections of COVID-19 fare better against Omicron since these antibodies are not based on just the spike protein, but the ‘whole’ virus.
In other words, while the body produces antibodies only against the spike protein in case of vaccination, it produces antibodies against the whole virus in case of an actual infection.
Moreover, the quantum of change between the original virus and Omicron, when the virus is taken as a whole, is considerably lower than when only their spike proteins are considered.
For example, out of the 50-plus mutations identified in Omicron, more than 30 are concentrated on the spike protein, leaving the rest of the virus largely intact.
Therefore, infection-generated antibodies against the ‘whole virus’ continue to retain some of their firepower even against Omicron.
Even non-mRNA vaccines, such as those used in India, include only the virus’ spike protein, and do not include the whole virus.
This is different from vaccines against diseases like smallpox, which contain the whole virus and not just a protein.
It is possible to create such whole virion vaccines against COVID-19 too, but it would take several years to come up with such a vaccine. Therefore, companies focused on including only the spike protein in their vaccines.
Overall, said the researchers from AHRI, there was a drop of a whopping 41-fold in the effectiveness of the Pfizer-BioNTech vaccine.
In fact, a 3-fold decline was seen in its effectiveness against the Beta variant of SARS-CoV-2, which emerged earlier this year, pointed out the scientists.
The latest study involved 12 people, six of whom were fully vaccinated with the Pfizer vaccine and six of whom were also previously infected by the virus, besides being vaccinated.
While the virus escaped the antibodies in case of the six non-infected people, the immune escape was incomplete in case of those who had been infected. The study did not include anyone who was infected, but not vaccinated.
“The results we present here with Omicron show much more extensive escape. However, escape was incomplete in participants..due to previous infection. Previous infection, followed by vaccination or booster is likely to increase the neutralization level and likely confer protection from severe disease in Omicron infection,” the scientists said in a prepublication paper.
On a positive note, the test also established that the virus is not yet able to penetrate regular human cells, and continues to depend on cells — such as those found in the lungs — that have a lot of ACE2 receptors on their surface for entry.
“We observed that Omicron infected the ACE2-expressing cells in a concentration dependent manner but did not infect the parental H1299 cells, indicating that ACE2 is required for Omicron entry,” they said.