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BA.4 and BA.5 Variants of Omicron Responsible for Rise in U.S. COVID Cases


The related omicron subvariants BA.4 and BA.5 that emerged in the Republic of South Africa are now the predominant strains in the U.S.  At the beginning of June CDC estimated that BA.5 accounted for seven percent of cases rising to 70 percent for the two subvariants combined at the beginning of July.  Studies conducted in the U.S. and South Africa show that the two subvariants are capable of evading immunity from previous exposure to COVID or from vaccination.  Both subvariants show increased transmissibility compared to Omicron BA.1.  It is estimated that BA.5 has the potential to increase incident cases to the high level recorded in January following the appearance of this strain. During the first week of July the average number of cases attained 105,000 per day.


On the positive side, neither BA.4 nor BA.5 appears to be more pathogenic than other Omicron variants.  South Africa noted an increase in hospitalizations as a result of the mutation of SARS-COV-2 to BA.5 but mortality remained at a constant level.


In response to the new Omicron subvariants, FDA has requested vaccine manufacturers to modify mRNA vaccines to provide enhanced protection.  It is anticipated that more effective vaccines will be available in the fall to mount a National booster campaign.


The poultry industry is well aware of the ability of coronaviruses to undergo mutation and to demonstrate a range of tissue tropism.  Variants of infectious bronchitis are constantly emerging, impacting the respiratory or reproductive tracts with evidence of prolonged shedding.  At the present time, the deleterious effects of IB are constrained by administration of live vaccines as primers followed by an inactivated oil emulsion booster for parents and commercial egg flocks. Live attenuated vaccines are administered sequentially to commercial broiler and pullet progeny to extend maternal immunity. 


The current practice of administering live attenuated vaccines to large concentrations of chickens although relatively effective over the past 70 years will have to be reevaluated. It is possible that research on SARS-CoV-2 may possibly lead to introduction of broad-spectrum mRNA infectious bronchitis vaccines applying technology developed during the past three years to control COVID.  At this time all mRNA vaccines are administered by the parental route. More effective alternative vaccines that can be administered by the spray route will be required to protect commercial flocks.