Coronavirus cases are skyrocketing, especially in China and the United States, where two predominant variants of omicron have appeared: BF7 and XBB.1.5, which some call ‘Kraken’. What should we keep in mind regarding vaccination?
Variants and subvariants of omicron: what do we know about them?
Since the SARS-CoV-2 omicron variant, scientifically named B.1.1.529, emerged and displaced predecessors such as alpha or delta, no new ones have appeared. But subvariants (or sublineages) of omicron have emerged. In summer, BA.2, BA.4 and BA.5 circulated in Europe. The latter was the dominant one, since it had a high transmission capacity, although it caused a mild form of the disease.
However, with the arrival of winter and the drop in temperatures – and given that SARS-CoV-2 behaves like a seasonal virus – the number of COVID cases has risen, especially in China and the US. In the Asian country, the predominant variant is still BA.5, but a sublineage has appeared, BF7, likely responsible for the very high number of cases this Christmas.
As for the United States, the appearance of XBB.1.5, dubbed Kraken, would explain the jump from producing 2% to 27% of total infections in just one month. This subvariant has been sequenced in a significant number of cases in 38 countries, such as the United Kingdom and Denmark.
The reason for this explosion of infections is due to the fact that it has the highest transmission capacity of all the omicron variants. Its different denomination indicates that it has arisen from a recombination of two other sublineages: BA.2.10 and BA.2.75. characterized by a mutation in the protein spike (S486P), that is, precisely in the receptor-binding zone of the cells.
However, it is not predictable that it will become the dominant subvariant, neither in the United States nor in Europe, as the European Center for Disease Prevention and Control maintains.
Should we worry about the appearance of these subvariants?
Actually, the appearance of subvariants is something normal in viruses that circulate among the population. The same happens in winter with seasonal viruses, since their strategy is to mutate. Added to this is the fact that people can be infected with different variants of SARS-CoV-2 at the same time, which favors the variants recombining with each other and originating subvariants such as XBB.1.5, detected in October 2022.
What can we do to keep the numbers of circulating viruses down, especially in winter? Getting vaccinated is a very good measure. That is why it has been proposed in autumn 2022 that risk groups be immunized with a new booster dose. Currently in Spain, the age group over 60 years of age has already been covered.
Why has this explosion of cases emerged in China and the US?
The situation in both countries is different. In China, the population had been confined throughout the pandemic by the strategy called “COVID zero”. For this reason, the population has not had exposure to the virus, only contacts between regulars.
Added to this is a complete vaccination rate in people over 65 years of age of no more than 40%. On the other hand, the vaccines used and manufactured in China (Sinovac and Sinopharm, both of the inactivated virus type) are much less effective: 58% efficient against symptomatic infection and 79% for severe cases. This distances them from the immunizations used in the West, whether they are RNA (Pfizer or Moderna, with efficiencies between 93 and 98%) or adenovirus (Astrazeneca or Jansen, between 80 and 92%).
The vaccines manufactured in China require more doses to obtain some protection and it is advisable to combine them with others of RNA or protein, which has not happened in this country. All this explains why, after the end of the confinement, the cases have skyrocketed.
In the US, since the population has not been confined for more than the initial three months, its citizens have subsequently been exposed to circulating viruses. In addition, 69% of the population has been vaccinated with complete regimens in adequate percentages, and 15.4% of people five years of age or older have received booster doses.
It is true that the number of cases has gone up a lot in the last month, with more than 38,000 hospitalizations today. However, this situation was to be expected after the end of the Christmas holidays, where there are more interactions in closed places. Added to this are the low winter temperatures, which facilitate the circulation of circulating viruses, and the appearance of a subvariant with more transmission, the aforementioned XBB.1.5.
The recommendations are to increase vaccination rates in those people with incomplete regimens and boost booster doses for those over 65 years of age and individuals with some immunosuppression.
Are there reasons to be alarmed?
The current situation in Spain is much better: 92.9% of those over 12 years of age have the complete vaccination regimen and 55.7% of the population have received booster doses. In addition, 56% of minors between 5 and 11 years old have a puncture.
At the beginning of January, the statistics indicated that the new diagnosed cases were 9,220, of which 3,520 required hospitalization for COVID and 231, admission to the ICU.
These data suggest that the outlook is good and that the arrival of passengers from countries with high infection numbers should not be cause for alarm. However, due to the lack of data, collecting COVID samples from travelers from China to sequence them is scientifically interesting if we want to know the evolution of omicron subvariants.
Do vaccines protect us against new variants and subvariants?
The companies Pfizer/Biontech and Moderna made bivalent vaccines available to the countries for booster vaccination in the fall. In addition to protecting against the original SARS-CoV-2 virus, they immunize against the omicron variants BA.1, BA.2, BA.4 and BA.5. In Spain, the chosen booster vaccine was the bivalent Pfizer/Biontech vaccine for the population over 65 years of age.
For those highly immunosuppressed who do not respond well to vaccines, the drug Evusheld is available, which combines two human monoclonal antibodies (tixagemimab and cilgavimab) that target the protein spike del virus SARS-CoV-2.
However, this drug may not protect against omicron variants and subvariants, so it is recommended that these patients wear masks and be very aware of the symptoms of contagion.
Regarding booster vaccines and their ability to protect against subvariants, two recent studies detail that these immunizations generate good humoral immunity, antibodies, and suggest adequate cellular immunity against the virus, especially in the response of cytotoxic lymphocytes. CD8.
The first study analyzed the ability of bivalent RNA booster vaccines to induce neutralizing antibodies against the BA.2.75.2, BQ.1.1, and XBB variants and subvariants. According to their results, people who received booster doses with these vaccines were better prepared for their antibodies to neutralize the omicron subvariants than those who received them with the original monovalent vaccines.
The other work evaluated the cellular immunity generated by the BA.1, BA.2, BA.4 and BA.5 variants and the original omicron strain. This study demonstrated that no variant escaped immunity, since the regions of the Spike protein that induced the best cellular immune cytotoxic response were the same in all variants. This had not changed from the original strain, which means that these regions are conserved in the virus and its variants. The reason is that the pathogen does not need them to enter the cell, which is where the mutations accumulate.
All these findings make scientists and academics confident in the protection of bivalent RNA vaccines against omicron variants and subvariants. However, the results of the SWITCH ON study among healthcare personnel, which will reveal the full immunogenicity induced by the booster dose with bivalent vaccines, have not yet been revealed.
In short, the only message to convey is tranquility. First of all, it is necessary to continue with the regimen of booster doses so that the group over 50 years of age reinforces their protection against the virus and avoid high numbers of circulating viruses. And secondly, we must apply common sense with other prevention measures such as the WHO recommendation for the use of masks indoors and on public transport, and if possible, work for better indoor air quality.
Carmen Álvarez Domínguez, Biochemist and molecular biologist, immunologist, vaccine expert and research professor in Health Processes at the Faculty of Education and in Advances in Infectious Diseases and antimicrobial therapy at the Faculty of Health Sciences, UNIR – International University of La Rioja
This article was originally published on The Conversation. read the original.
