BA.4 and BA.5 transmit faster and can reinfect people with previous Omicron infections more easily
“BA.4 and BA.5 are about 9 per cent more transmissible than BA.2 per day, based on the latest data from South Africa,” states Dr. Sarah Otto, Co-Lead, CoVaRR-Net Computational Analysis, Modelling and Evolutionary Outcomes (CAMEO) Pillar, Canada Research Chair in Theoretical and Experimental Evolution, and Killam University Professor, University of British Columbia. Because of their additional mutations and where they are located within the virus, BA.4 and BA.5 appear to evade immune protection from previous infections, including infections from BA.1 that drove the first Omicron wave. “That means there is a higher chance of contracting BA.4 or BA.5, even if you were recently infected with BA.1, although vaccination on top of a recent Omicron infection, is very highly protective against these variants,” says Dr. Otto.
In South Africa, many people were infected during the first Omicron BA.1 wave, but there wasn’t a second BA.2 driven wave, and so reinfections rates with B.4 and BA.5 are fairly high there. It is hard to predict how these new lineages will spread in countries, like Canada, that had a more recent BA.2 wave as well. “In Canada, there have been two big Omicron waves, primarily BA.1 and then BA.2. Plus, 48 per cent of Canadians have received a booster dose, so we have a pretty big wall of immunity built up that will help protect us from BA.4 and BA.5 in the near future,” says Dr. Otto.
She notes there is a lot that remains unknown, however, with few studies looking at BA.2 infections to see how much protection they offer against BA.4 and BA.5. “We’re keeping an eye on what happens with BA.4 and BA.5 infections and hospitalizations around the world and nationally, and with other subvariants, such as BA.2.12.1, first detected in the United States, and BA.2.21, first detected in Canada, which are both rising in frequency,” says Dr. Otto.
Will current vaccines be effective against BA.4 and BA.5?
Third or fourth doses boost antibody levels, thereby offering greater protection against infection, severe disease and death from all variants, including BA.2, BA.4 and BA.5. “There is no indication yet of any difference in the severity of infection or illness caused by BA.4, BA.5, or any of the new BA.2 sublineages, compared to previous Omicron subvariants. Current vaccines are protecting people very well against severe disease and hospitalization from Omicron variants. But people need to get additional doses when they become eligible to stay protected from getting infected,” says Dr. Otto. “Getting additional doses, as well as wearing masks and avoiding crowded indoor spaces with poor ventilation, are all actions we can take to lower the risk of infection and curb transmission.”
Preparing for a fall wave
“Another wave is likely to hit Canada in the fall – if not sooner – because antibody levels fall over time. In addition, because these variants are so different, we should expect these variants, or others, to drive future rounds of infections. But we don’t know whether these future waves will be similar to Omicron or not. We need to keep a watch out for lineages that could be both more transmissible and more virulent,” says Dr. Otto.
Next-generation vaccines and antivirals to help fight new variants and reduce transmission are being developed
“Progress is being made in developing and delivering next-generation vaccines through multiple platforms, which can offer long-lasting protection and be broadly protective against existing SARS-CoV-2 variants and future unknown variants,” says Dr. Arinjay Banerjee, Deputy, CoVaRR-Net Host-Pathogen Interactions Pillar, Early Career Investigator and Research Scientist, Vaccine and Infectious Disease Organization (VIDO) and Adjunct Professor, University of Saskatchewan.
For example, a nasal spray vaccine that works through the mucosal lining of the airways to neutralize the SARS-Co-V-2 virus offers the potential of protecting against disease and transmission by training a different part of the immune system. “By activating mucosal immunity, you can induce a strong immune response at the site of infection. This is a respiratory pathogen, so you want an immune response in your airway. The immune response can neutralize the virus before it has a chance to take hold,” says Dr. Banerjee.
Some intranasal mucosal vaccines being developed are designed to tackle multiple variants and could help neutralize new strains of the virus, acting as a complement to current intramuscular vaccines, while reducing transmission as well. “Another benefit is that you could have higher uptake with this non-invasive method of delivery compared to a needle,” adds Dr. Banerjee.
Better antiviral drugs could also help to limit transmission and slow the emergence of new variants. “Broadly effective antiviral drugs are critical in helping to protect against severe disease and limit transmission of future unknown variants. Antiviral drugs can be stockpiled and deployed the moment there is an outbreak of a new variant or in the event of the emergence of a novel coronavirus in a post-COVID world. If we had more broadly effective antiviral drugs, we could treat people in the early stages of an outbreak while vaccines are being developed and deployed,” says Dr. Banerjee.
For now, vaccines and antivirals are helping us to protect ourselves against severe disease from continually evolving Omicron subvariants, and we’ll see what the future holds in terms of next-generation vaccines and better, broad-spectrum antivirals.