An introduction to the new Covid-19 variants
CLINICAL MATTERS
Covid-19 drags on to confound efforts to end the pandemic by mutating into more contagious forms. Fortunately, vaccines persist to protect against severe diseases. Hospitalization rates remain much less than that during our Delta wave because of widespread vaccination. Two doses of vaccine, however, are no longer enough. The first booster in adults is needed to ensure continued high-level defense from severe disease. A second booster dose may help ensure better protection for the elderly and the immunocompromised. With lagging rates of boosting nationwide, there is a potential threat of a significant spike in severe cases as more and more people are now six months or more out from their second dose.
With the local detection of the new Omicron sublineages, including BA.2.12 and BA.2.12.1, our genomic surveillance program led by the Philippine Genome Center (PCG) continues to do its job at picking up potentially problematic variants of concern (VOCs). Preliminary data suggest that these sublineages are about 23 to 27 percent more contagious than BA.2. The BA.2 that drove our Omicron wave in January 2022, is more contagious than BA.1, which is responsible for most initial Omicron outbreaks worldwide. Despite the increased risk of transmission, there is no evidence that these sublineages cause worse diseases or are more prone to bypass immunity from vaccination.
The first and only BA.2.12 case detected in the Philippines was in a Finnish national in Baguio with mild symptoms. She recovered and there were no other instances of confirmed infection among her close contacts. The initial cases of BA.2.12.1 were detected in a cluster in Palawan involving 11 foreign nationals and one returning overseas Filipino on a boat trip. Two local cases were found in Metro Manila while another three cases were from Iloilo province. Most were vaccinated and none of the cases developed severe diseases. This shows how vaccination and boosting continue to protect against severe diseases even with the new Omicron sublineages.
On May 17, the Department of Health (DOH) confirmed local transmission of BA.2.12.1 after the local cases in Iloilo could not be linked to an imported case. Local transmission is defined as Covid-19 transmission within a country without a clear link to an imported case, but the cases can still be linked to a local cluster. This is in contrast to community transmission where there are several large clusters that can no longer be linked with each other. At the time of this writing, DOH has not confirmed community transmission of either BA.2.12 or BA.2.12.1.
Despite these new VOC sublineage detections, case numbers remain low. After massive election rallies and the election itself, there is currently no clear indication of an impending surge. Daily numbers of new cases are in the range of 100 to 200 and are tantalizingly close to dropping down to double digits on some days. In Metro Manila, the average number of daily cases has remained below 100 for several weeks now. Active cases nationwide continue to go down and are currently in the 2,000s while active cases in Metro Manila are below 800 as of May 18. Even if the new VOCs may be slowly and stealthily spreading in the community, interventions, including masks and vaccination are continuing to protect our people.
Two other Omicron sublineages that are being closely monitored are BA.4 and BA.5. The BA.4 has just been detected in a returning overseas Filipino from the Middle East who was asymptomatic. Further investigation is ongoing. These sublineages were first described in South Africa between January and February of this year and are currently driving a spike in cases in several countries. BA.4 and BA.5 have identical spike protein mutations and may have a higher propensity to escape vaccine-induced immunity. It is estimated that BA.5 has a 12 to 13 percent advantage over BA.2. Due to these properties, the European CDC has declared BA.4 and BA.5 as variants of concern. WHO has not yet classified them as new VOCs, and they remain subsumed under Omicron, albeit under a new classification referred to as a Variant of Concern - Lineage Under Monitoring (VOC-LUM). There is no evidence that either BA.4 or BA.5 causes more severe diseases or new types of symptoms.
On May 15, Singapore announced the detection of two local cases of BA.4 and one local case of BA.5. All cases were asymptomatic or had mild symptoms. At least 16 countries have reported cases of BA.4 and BA.5, but Singapore is the closest to the Philippines that has previously detected these new sublineages.
While it may be inevitable that BA.4 and BA.5 will eventually make it into the community in the Philippines, there are enough public health strategies to mitigate the impact of these new sublineages. Predeparture testing remains an important intervention in screening out imported cases of Covid-19. While RT-PCR and antigen testing are not perfect, they do still catch infections in people who are incubating the virus and are asymptomatic, minimally symptomatic, or are concealing their symptoms. These screens out a substantial number of potential spreaders. Even those who get through are less able to spread disease since people continue to wear masks. The continued local mask mandate has been a key strategy in preventing spikes in cases despite increased mobility and mass gatherings. The strategy worked for BA.2.12. It remains to be seen if more BA.2.12.1 cases do crop up. Coupled with an aggressive vaccination and boosting strategy, our current Alert Level 1 status can be sustainable if everyone cooperates.
It is indeed fortunate that Filipinos do not mind keeping their masks on. We do still have to catch up with boosting, but the continued use of effective layers of prevention has truly flattened the curve.
Even if new lineages enter, it is unlikely the resulting spike will be significant enough to overwhelm our healthcare system or cause substantial severe disease and death. For many experts, the recently concluded elections were the true litmus test of our ability to live with the virus. If there are no further spikes toward the end of May, then it is very likely that we may never have to lockdown again.