Booster doses vaccine Pfizer/BioNTech and Moderna against COVID-19, which have been modified to target the BA.4 and BA.5 subvariants of the Omicron mutation, received US Food and Drug Administration (FDA) approval yesterday and are expected to follow shortly. will be launched.

How are the new vaccines different from the original ones and how effective are they? Two professors of pathology, microbiology and immunology at the University of South Carolina answered 5 critical questions.

1. How are the updated vaccines different?

The new vaccines are improved versions of the original COVID-19 vaccines introduced at the end of 2020. They use the same mRNA technology as the original vaccines. Their main difference is that the new vaccines can encode the spike protein of both the original SARS-CoV-2 strain and Omicron mutation variants. As of the end of August 2022, sub-options BA.4 and BA.5 prevail worldwide. Currently in the US, 89% of infections are due to BA.5 and 11% are due to BA.4.

2. How do new vaccines activate the immune response?

In COVID-19 infection, the virus uses a spike protein to enter cells. The spike protein triggers the production of so-called neutralizing antibodies that bind to it and prevent the virus from entering other cells. But when a virus mutates, the antibodies previously produced in response to it can no longer bind effectively to the mutated spike protein. In this regard, the SARS-CoV-2 virus acts like a chameleon, eluding the immune system. Ultimately, ongoing mutations cause antibodies produced in response to the original vaccine strains to become less effective over time in preventing infections caused by new variants.

3. How effective will the new vaccines be?

So far, there are no human studies on the effectiveness of the new updated vaccines in preventing reinfections and providing long-term immune protection. However, in human clinical trials and laboratory studies, both Pfizer/BioNTech and Moderna found that a version of the new vaccine against the original SARS-CoV-2 virus and the earlier Omicron strain, BA.1, elicited a strong immune response and provided more protection against both the parental strain and variant BA.1.

In addition, the companies reported that the same vaccine combination elicited a significant humoral response against the newer BA.4 and BA.5 sub-variants, although this response was lower than against BA.1. Based on the available data on previous vaccines, it is very likely that the new booster versions will continue to provide strong protection against serious illnesses that can lead to hospitalization or death. But whether they protect against re-infection and primary infection remains to be seen in practice.

4. Will they only be used as booster doses?

Renewed vaccines can only be used as a booster two months after the completion of the initial vaccination schedule. The Moderna vaccine is approved for use in people 18 years of age and older, while the Pfizer vaccine is for people 12 years of age and older. The newer vaccines contain a lower dose of mRNA and are thus intended only for boosters. That is, people who have never been vaccinated against COVID-19 will not be able to get them.

5. Will they protect against future variants of the virus?

How well the updated vaccines will work against new variants that may arise will depend on the nature of future spike protein mutations. If it is a small mutation compared to the original strain or variants BA.4 and BA.5, the new doses will provide good protection. However, if the hypothetical new strain has completely new mutations in its spike protein, then it is possible that the virus could again evade immune defenses.

On the other hand, the successful development of updated vaccines demonstrates that mRNA technology is innovative enough that, within months of a new variant being introduced, new formulations specifically designed to combat the emerging variant can now be developed and marketed.

^{Source: Conversation}