Countries and regions such as Singapore, Hong Kong, and New Zealand, which were able to keep their number of COVID-19 cases under control for most of the pandemic, are currently experiencing a surge in cases.
These countries previously adopted a COVID-19 eliminationTrusted Source strategy or a “zero-COVID” policy, which aimed to reduce the incidence of new cases to naught. This policy involved strict rules involving border controls, contact tracing, mass testing, quarantine, and self-isolation.
Dr. Michael Baker, a professor of public health at the University of Otago, Wellington, told Medical News Today that this elimination policy pursued by many countries in the Asia-Pacific region was “generally very successful during the first 12-18 months of the pandemic when vaccines were not widely available.”
“Keeping COVID-19 cases at very low levels for much of this time has resulted in low hospitalizations and deaths, and has protected the economies in many jurisdictions in this region, including China, Hong Kong, Taiwan, Singapore, Australia, and New Zealand,” he added.
He said that the wide circulation of Omicron had forced Singapore, Australia, Hong Kong, and New Zealand to transition from elimination to mitigation approaches.
The emergence of the Omicron BA.2 subvariant, which initial reports suggest is more transmissible than BA.1, may be at least partly responsible for the recent surge in COVID-19 cases in these countries.
While mortality rates due to COVID-19 have remained relatively low in most nations that previously implemented a “zero COVID-19” policy, Hong Kong recently reported the world’s highest COVID-19 death rate over a 7-day period.
According to experts, a major reason for a large number of hospitalizations and deaths in Hong Kong is the low vaccination rate in the vulnerable older population.
Although vaccination rates among the general population are reasonably good, a significant percentageTrusted Source of the older population remains unvaccinated, which may partly explain why COVID-19 cases skyrocketed in February.
New Zealand, in contrast, has kept its hospitalizations and deaths low despite a surge in cases. This is likely due to immunity, experts say, as New Zealand currently has one of the highest vaccination rates in the world, with 95% of individuals over the age of 12 years vaccinated.
“Those countries that were able to achieve high vaccine coverage before entry and widespread circulation of the Omicron variant have been able to keep their hospitalization and death rates low. That is the case in New Zealand in particular, which still has the lowest COVID-19 mortality rate in the OECD,” Dr. Baker noted.
In contrast to other Asian countries, mainland China has persisted with the elimination policy, and there have been outbreaks due to Omicron, especially in the Jilin province and the city of Shenzhen. Yet, the number of deaths due to COVID-19 has been limited so far, and the following few weeks will determine China’s ability to persist with the policy.
Many European nations — including Germany, the U.K., France, and the Netherlands — have also been experiencing a COVID-19 surge due to the BA.2 variant. The U.K., for example, reported a 7-day average of over 89,000 cases and 127 deaths as of March 18, 2022.
Experts believe that prematurely removing protective measures against COVID-19 may have contributed to this rise in BA.2 infections. The higher contagiousness of the subvariant and waning immunity from either vaccines or previous SARS-CoV-2 infections may have also played a part.
Previous waves of SARS-CoV-2 infections in Europe have often played out similarly in the U.S., albeit a few weeks later. Both regions have also employed similar pandemic strategies: a mitigation policy focused on limiting the spread of SARS-CoV-2 in the community rather than complete elimination.
There have been some signs of an increase in COVID-19 cases in the U.S.
Early signs of BA.2 in wastewater
The proportion of COVID-19 cases due to the BA.2 variant increased from 12.6% to 22.3% between March 5-12, 2022. Despite a declineTrusted Source in cases and hospitalizations in recent weeks, wastewater samplesTrusted Source collected from certain communities suggest a potential increase in COVID-19 cases in the forthcoming weeks.
CDC wastewater surveillance data indicate an increase by at least 10% in SARS-CoV-2 levels at 162 out of the 469 active sites.
“Since there have been some concerning epidemiological data in recent weeks including increased viral RNA levels in wastewater and increased cases in some locations around the country, there may be an increase of COVID-19 cases this spring similar to what several countries in Europe are seeing,” said Dr. Hamer.
Although experts expect an uptick in COVID-19 cases in the U.S. due to the BA.2 subvariant, there is a lack of certainty about its extent. This uncertainty stems from the differences between the current pandemic situations in the U.S. and Europe.
For instance, some European nations, such as Spain, have had stringent COVID-19 restrictions, including outdoor masking, which were only lifted recently.
Since its emergence, the BA.2 variant has been competing with other Omicron subvariants BA.1 and BA.1.1 and is proving to be more transmissible.
“The data from other parts of the world suggest that BA.2 is highly contagious, but not more severe than BA.1. There have been some reports of BA.2 reinfecting individuals who were recently infected with BA.1, but this seems to be relatively rare,” Prof. Lauren Ancel Meyers, director of the University of Texas at Austin’s COVID-19 Modeling Consortium, also told MNT.
“In projecting what might happen in the coming weeks, we have to consider both the infectivity of BA.2 and recent policy and behavior relaxation in the U.S. that might fuel more rapid transmission,” she added.
Yet the Rockefeller Foundation’s Pandemic Prevention Institute has pointed out that the BA.1.1 subvariant has been more prevalent in the U.S. than in the U.K.
It notes that BA.1.1 has been the dominant Omicron subvariant in the U.S. and that the increase in the prevalence of BA.2 has been more gradual. In other words, the rise of BA.2 seems to have followed a different trajectory so far in the two nations.
Sewage samples not worrying
The Pandemic Prevention Institute has also pointed out that the CDC’s wastewater surveillance data only reveal a relative increase in SARS-CoV-2 RNA levels. Thus, if the initial viral RNA levels in sewage samples were extremely low, even a 1,000% increase would only suggest a modest increase in actual cases.
“Based on what we are currently seeing, I do not expect the presence of BA.2 to drive a surge in cases in the near future. With both Delta and Omicron, there was a very clear pattern. We would detect the new variant in the wastewater from a community, and within 2-3 weeks there was a surge in SARS-CoV-2 RNA in wastewater which coincided with an increase in patients. This pattern was very predictable,” said Dr. Marc Johnson, a virologist at the University of Missouri.
Dr. Johnson said his observations so far have not indicated a similar scenario:
Although COVID-19 case patterns in the U.S. have largely echoed those in the U.K., as the spread of the Alpha variant showed, that has not always been the case.
“The ‘BA.2 wave’ looks a lot more like the Alpha wave in Missouri. Exactly 1 year ago, Alpha (B.1.1.7) was slowly moving through our state and displacing all of the other lineages. However, it never caused a surge in cases like it did in Europe,” Dr. Johnson emphasized.
Although Omicron and its subvariants seem to cause less severe disease than previous SARS-CoV-2 variants, the high death rates in Hong Kong underscore the importance of immunity — both from COVID-19 vaccines and prior SARS-CoV-2 infections.
Although the protection conferred by COVID-19 vaccines against infection with Omicron tends to wane after a few months, evidence suggests that COVID-19 vaccines remain effective at preventing severe disease.
However, the lower vaccination rates in the U.S. compared to the U.K. have raised concerns about the potential toll of a second Omicron wave.
In the U.S., about 65% of individuals are fully vaccinated, and only 44.6% have received the booster shot. In contrast, around 85.8% of eligible individuals in the U.K. have been vaccinated, and 67.3% have been immunized with a booster shot.
Dr. Hamer said vaccine rollout was crucial in states with low coverage.
“The U.S. needs to continue widespread testing, figure out ways to allow people who self-test at home to have their antigen tests results make it into the broader public health surveillance systems, continue sequencing a reasonable proportion of positive samples, and carefully track the impact of rising cases on hospitalization rates — and be ready to reinstate mask mandates if the situation greatly worsens,” he advised.