In what could further underline the importance of vaccination, a new study shows that infection with the Omicron variant of the Covid virus may not generate broad immunity in unvaccinated individuals who may protect against other variants.
However, the US pre-print study shows that in vaccinated people, an Omicron infection can boost existing immunity, allowing the individual to better fight off another infection.
The study was conducted by a team including Nobel laureate Jennifer Doudna, researchers from the University of California, San Francisco; University of California, Berkeley; California Department of Public Health; and Covid-19 testing startup Curative Inc.
According to the study, mice were infected with the type of virus first identified in the United States in 2020, the Delta variant and the Omicron variant, and tested whether their serum (a blood component) could effectively neutralize or fight against the original virus, and the Alpha (first found in the UK), Beta (first found in South Africa), Delta (first found in India) and Omicron (found for the first time in South Africa).
The researchers found that mice infected with Delta developed the best protection against other variants, with the exception of the Beta variant which is known to be highly immune evasive. In contrast, infection with Omicron was only effective in combating the Omicron variant but did not sufficiently neutralize – meaning it did not effectively protect against – other variants, according to the study. .
On the other hand, sera from mice infected with the original virus could effectively protect against another infection with the same virus, as well as the Alpha and Delta variants. It could not effectively protect against Beta or Omicron infections.
Almost all of the vaccines currently in use use modified spike proteins from the wild type of the virus to trigger an immune response. This could be one of the reasons why Omicron causes a high proportion of breakthrough infections in fully vaccinated individuals.
Vaccines, however, remain effective against serious illness and death. Several countries, including India, have started administering a third booster to provide better protection for the most vulnerable.
After the mouse study, the researchers used sera from those who had a breakthrough infection during the Delta wave and the Omicron wave to see their degree of protection against the wild type as well as against all other variants.
Sera from those with breakthrough Delta infection (infection after full vaccination) could effectively neutralize all variants, although neutralization was weak for Omicron.
But the researchers also realized that sera from confirmed Omicron infection conferred good protection against all variants.
“These results suggest that Omicron infection can effectively boost existing immunity conferred by vaccination against other variants, eliciting a ‘hybrid immunity’ that is effective not only against itself but also against other variants” , the researchers noted.
The researchers stated that since Omicron infection alone could not provide broad protection against all variants, but could enhance existing immunity, and Delta could create broad immunity, multivalent vaccines using both Omicron and Delta could be developed in the future.
Dr Anurag Agarwal, Director of the Institute of Genomics and Integrative Biology, said: “Omicron is not a natural vaccine. Infection with Omicron does not provide protection against infection with other variants in unvaccinated individuals. Previously reported effects against Delta were due to the enhanced immune response induced by the vaccine which protects well against earlier variants.
He said people should not confuse the virus which is known to cause milder upper respiratory tract symptoms in most patients with a natural vaccine, as it can still cause serious illness and death in people whose the immune system is weakened.
K Srinath Reddy, Chairman of the Public Health Foundation of India and member of the National Covid-19 Task Force, said: “This would mean that if Omicron itself has immune evasion capability due to 36 spike protein mutations , the limited immunity it evokes adds to previous spike protein immunity and may result in a sufficiently protective effect against serious disease.
Dr Samiran Panda, who heads the Department of Epidemiology and Communicable Diseases at the Indian Council of Medical Research and is also part of the task force, said: “The results are interesting, but we cannot extrapolate the results from a one-population mouse model. as big as India. We have to wait and see what will happen. Of course, when there is antigenic exposure, there will be immunological changes. »