“Most Transmissible Variant” BA.2 Expected to Overtake Original Omicron Strain

US health experts are predicting an increase in COVID-19 cases amidst the rise of the BA.2 variant. BA.2 is now responsible 75% of new COVID-19 cases worldwide, and 23.1% of cases in the US.

Currently, COVID-19 infections are at the lowest they have been since July 2021. However, rising numbers in China, Australia, and the UK are leading some to predict the US will follow suit. “This is the most transmissible variant we have seen of the SARS-CoV-2 virus to date,” said Maria Van Kerkhove, MD, of the World Health Organization (WHO)

The WHO reported last month that the difference in transmissibility between BA.1 and BA.2 is less than the difference between BA.1 and Delta. Anthony Fauci, MD, the White House chief medical adviser, said BA.2 is approximately 50-60% more transmissible than the original Omicron variant.

It is still unclear whether BA.2 causes more severe illness, hospitalization, and deaths than other COVID-19 variants. Early reports show that like Omicron, BA.2 causes less severe disease. However, one study in hamsters found BA.2 to be more pathogenic than BA.1.

Notably, even if BA.2 is “less severe,” like Omicron, its highly infectious nature means many people will still become extremely or deathly ill, overwhelming hospital resources. Thus, COVID-19 vaccination is still recommended as the best defense against all current variants.

Fauci explained that BA.2 is more transmissible, “However, when you look at the cases, they do not appear to be any more severe and they do not appear to evade immune responses either from vaccines or prior infections.”

The BA.2 variant is also called “stealth Omicron,” due to its ability to evade detection. Initially, the many similarities between BA.1 and BA.2 complicated genomic sequencing. BA.2 differs from BA.1 in its genetic sequence, with amino acid differences in proteins, including the spike protein. Statistical analyses show the effective reproduction number of BA.2 is 1.4-fold higher than BA.1.

Although BA.2 will almost certainly cause cases to increase in the US and worldwide, not all experts are predicting infections to spike as dramatically as they did earlier this year. The massive BA.1 wave means approximately 73% of Americans may now be immune to Omicron. However, those who have not gotten a COVID-19 booster shot, the immunocompromised, and people over 65 years of age are particularly vulnerable.

Though there have been documented cases of BA.2 reinfection after prior COVID-19 infection, initial data suggests infection with BA.1 provides “strong protection” against reinfection with BA.2, according to the WHO.

“COVID-19 vaccines remain the best public health measure to protect people from COVID-19 and reduce the likelihood of new variants emerging,” the US Centers for Disease Control and Prevention said. The CDC’s Vaccine and Related Biological Products Advisory Committee (VRBPAC) is scheduled to meet on April 6 to discuss the necessity of additional booster shots amidst waning protection against these more infectious variants.