The subvariant of Omicron called BA.2 is now the dominant strain of the COVID-19 virus in the United States, according to the Centers for Disease Control and Prevention (CDC).

BA.2 is about 33% more contagious than BA.1 — the Omicron variant that caused the U.S.’s winter surge — and now represents more than 70% of all COVID-19 infections in the country. In Oregon, scientists believe BA.2 is trending similar to national estimates and will know more in the coming weeks.

Both nationally and at the state level, experts generally agree that BA.2 is unlikely to cause a large surge like BA.1 did. Cases and hospitalizations are expected to rise, but likely not to levels that disrupt our health care system.

BA.2’s impacts

Although it’s not clear how BA.2 will ultimately affect the U.S. or Oregon, scientists can look to other countries to examine the possibilities. In the United Kingdom, for example, BA.2 became dominant in late February. So far, the subvariant has caused a rise in cases and hospitalizations there but has not caused a major increase in deaths.

Data from the U.K., the rest of Europe and other countries such as Israel show that BA.2, while more contagious, doesn’t appear to cause more severe disease than BA.1.

And because many people in Oregon are up to date with their recommended COVID-19 vaccines (primary series plus a booster dose), have been infected by BA.1, or both, much of the state’s population has some level of immunity to BA.2 for the next three months or so. Moreover, recent infection with BA.1 likely provides significant protection against reinfections with BA.2.

Importance of boosters

At this stage in the pandemic, booster doses of COVID-19 vaccines are more important than ever. During the Omicron wave, booster doses provided strong protection against severe illness from COVID-19, lessened the strain on hospitals and saved lives. In a study this past winter, the CDC found that unvaccinated people 18 years or older with COVID-19 were five times more likely to end up in the hospital compared to those who received a primary vaccine series. When compared to those who’d also received a booster dose, unvaccinated adults with COVID-19 were seven times more likely to be hospitalized.

The CDC also recently reported that during the Omicron BA.1 surge this winter, third doses (either as a booster or an additional dose for immunocompromised people) were 87-91% effective against COVID-19-associated hospitalization or ER/urgent care visits.

Monitoring BA.2

Public health experts are keeping a close eye on BA.2 spread at the community level in Oregon. Along with genetically sequencing positive COVID-19 tests, scientists are also monitoring wastewater data because we shed virus in our urine and feces. Wastewater samples are regularly tested at 39 wastewater treatment plants across the state. That way, even if positive test rates are low because of barriers to access or people aren’t reporting their positive home-test results to health officials, scientists can see exactly where levels of the virus are rising.

If BA.2 virus levels start rising in Oregon’s wastewater, public health experts can predict that a rise in cases will follow over the subsequent few weeks.