The most transmissible variant to date of the coronavirus is threatening a new wave of infections in the United States, even among those who have recently recovered from the virus.
The Omicron subvariant known as BA.5 is now dominant, according to federal estimates released Tuesday, and along with BA.4, another subvariant, is fueling an outbreak of cases and hospitalizations.
United States
East. share of Omicron variant cases
January 1
July 4th
50%
100%
BA.1
BA.2
BA.4
BA.2.12.1
BA.5
New cases per 100,000 people
January 1
July 4th
100
200
BA.5
Sources: CoVariants.org; GISAID; New York Times Database of Cases and Deaths | Note: The graphs show case averages of 14 days and the frequency of variants between cases is an estimate. Sequencing rates may reflect localized evidence-based trends in a particular region or hospital. The graphs show the latest available data, which may be delayed and may change as additional sequences are completed. Recent data is based on smaller samples and is especially likely to change.
While the popularity of home tests means that reported cases are a significant count of the actual infection rate, the proportion of tests that test positive is increasing and is now higher than during most other waves of pandemic. According to the CDC, the risk of Covid-19 is increasing in much of the country.
“I think there’s an underestimation of what it will do in the country, and it’s already exerting its effect,” said Eric Topol, a professor of molecular medicine at Scripps Research, who has written about the subvariant.
BA.5 and BA.4, both subvariants of the Omicron variant that ravaged the world during the winter, are the most capable versions of the virus to date to evade immunity from previous infections and vaccines. Both variants have mutations in their spike proteins that are quite different from previous versions of the virus because they are able to dodge some antibodies.
The waves of infection, and the consequent immunity that accompanies them, vary from country to country and allow for imperfect comparisons. Vaccination rates also vary. But in places where BA.4 and BA.5 have been dominant for weeks or months, subvariants have led to increased cases and hospitalizations, despite some population immunity to previous waves.
Hospitalizations for Covid-19 per 100,000 people
South Africa
January 1
July 4th
25
50
BA.4 + BA.5
dominant
Sources: Our World in Data, CoVariants.org, Centers for Disease Control and Prevention, U.S. Department of Health and Human Services. | Note: The time periods in which BA.4 and BA.5 become dominant are estimates.
The CDC says so far there is no evidence that BA.4 or BA.5 is inherently more severe than other Omicron subvariants, but when more people become infected, the number of people hospitalized because of the virus can also increase.
Pre-infection with another form of the Omicron variant confers some degree of immunity, Dr. Topol said, and this may explain why cases have not yet skyrocketed in the United States. “But it’s nothing like what we expect,” he said. Omicron subvariants appear to represent a deviation from previous waves of the virus, when previous infection was more likely to protect against reinfection.
In Portugal, where vaccination rates are higher than in the United States, cases rose sharply after BA.5 became dominant in May and hospitalizations approached their previous high Omicron.
Portugal
East. share of Omicron variant cases
January 1
July 4th
50%
100%
BA.1
BA.2
BA.5
NAS SEQUENCE DATA
New cases per 100,000 people
January 1
July 4th
200
400
NAS SEQUENCE DATA
Sources: CoVariants.org; GISAID; New York Times Database of Cases and Deaths | Note: The graphs show 14-day case averages and variant frequencies are CoVariants estimates, grouped at two-week intervals. Sequencing may reflect localized evidence-based trends in a particular region or hospital. The graphs show the latest available data, which may be delayed and may change as additional sequences are completed. Recent data is based on smaller samples and is especially likely to change.
Before BA.4 and BA.5 became dominant in South Africa in April, research suggested that 98% of the population had some antibody from vaccination or previous infection or both.
Even with these protective antibodies, many people in the country were still infected with BA.4 and BA.5, and subvariants caused a small increase in cases, hospitalizations, and deaths.
South Africa
East. share of Omicron variant cases
January 1
July 4th
50%
100%
BA.1
BA.2
BA.4
BA.5
NAS SEQUENCE DATA
New cases per 100,000 people
January 1
July 4th
25
50
NAS SEQUENCE DATA
Sources: CoVariants.org; GISAID; New York Times Database of Cases and Deaths | Note: The graphs show 14-day case averages and variant frequencies are CoVariants estimates, grouped at two-week intervals. Sequencing rates may reflect localized evidence-based trends in a particular region or hospital. The graphs show the latest available data, which may be delayed and may change as additional sequences are completed. Recent data is based on smaller samples and is especially likely to change.
Sites that have just emerged from the major spring waves of the virus may not be saved either. Several European countries had major outbreaks of a different Omicron subvariant, BA.2, which caused new waves of hospitalizations and deaths that peaked in April. However, in these countries, cases increase again as BA.5 becomes dominant.
United Kingdom
East. share of Omicron variant cases
January 1
July 4th
50%
100%
BA.1
BA.2
BA.5
NAS SEQUENCE DATA
New cases per 100,000 people
January 1
July 4th
100
200
NAS SEQUENCE DATA
France
East. share of Omicron variant cases
January 1
July 4th
50%
100%
BA.1
BA.2
BA.5
NAS SEQUENCE DATA
New cases per 100,000 people
January 1
July 4th
200
400
NAS SEQUENCE DATA
Italy
East. share of Omicron variant cases
January 1
July 4th
50%
100%
BA.1
BA.2
BA.5
NAS SEQUENCE DATA
New cases per 100,000 people
January 1
July 4th
100
200
NAS SEQUENCE DATA
Sources: CoVariants.org; GISAID; New York Times Database of Cases and Deaths | Note: The graphs show 14-day case averages and variant frequencies are CoVariants estimates, grouped at two-week intervals. Sequencing rates vary across countries and sometimes reflect localized evidence-based trends in a particular region or hospital. The graphs show the latest available data, which may be delayed and may change as additional sequences are completed. Recent data is based on smaller samples and is especially likely to change.
Experts say it is too early to fully predict what the latest subvariants may bring to the United States, which had an even more recent wave of viruses in May and June, driven by both BA.2 and another subvariant called BA. 2.12.1. High percentages of recent BA.2.12.1 infections such as that of the United States were uncommon among countries now experiencing waves of BA.4 and BA.5 infections.
The United States also has a lower vaccination rate than many of these countries and a much lower proportion of seniors who have had one or both booster injections.
“There’s a wave going on, no doubt about it,” Dr. Topol said. “My concern is duration.”