However, experts in South Africa, where the strain first emerged, and in the UK have said the variant is milder than previous versions of the virus. Scientists in the UK said those infected with Omicron are 70 per cent less likely to be hospitalised, but experts in South Africa said the figure may be as high as 80 per cent. However, it is unclear whether this is because the strain is inherently less severe or if protection from vaccines and prior infection mean people who catch Omicron are becoming less unwell.
Adults who received two AstraZeneca doses, plus a Pfizer or Moderna booster, are 60 per cent less likely to get symptoms than the unvaccinated if they catch Omicron up to four weeks after their third jab.
But after ten weeks, efficacy drops to 35 per cent for Pfizer and 45 per cent for Moderna. Meanwhile, those who received Pfizer for all three of their doses saw their protection levels increase to around 70 per cent for two weeks after their top-up dose before falling to around 45 per cent 10 weeks later. People given two AstraZeneca vaccines and a Moderna booster were the most protected, according to the report, with efficacy sitting at 75 per cent against Omicron and lasting for at least nine weeks.
He said: 'If we would not have brought in the measures in November , why are we doing it now? What's the specific justification for doing it? There would be no justification in having 'any restriction we didn't previously have' if the modelling is confirmed in the coming weeks, Professor Dingwall said. However, he noted that if the UK has two respiratory viruses in the population which are capable of producing significant levels of hospitalisation, the NHS may need more funding to deal with both Covid and flu to increase its capacity.
Washington University experts who made the claim that Omicron will cause 97 to 99 per cent fewer deaths than Delta — based on case and death data — admit their forecasts were more 'optimistic' than forecasts used by UK Government scientists. The Prime Minister was warned that daily Covid deaths in Britain could breach 6, a day this winter under the worst-case scenario of Omicron's rapid spread.
But the doomsday projection, conducted by one of the modelling sub-groups who feed into No10's SAGE panel, was branded 'fictitious'. Daily coronavirus fatalities maxed out at slightly less than 1, during the depths of the second wave, before ministers embarked on a huge vaccination blitz. And studies show two doses of the current crop of jabs still drastically cut the risk of patients becoming severely ill if they catch the virus, even if they offer little protection against falling ill in the first place.
Booster vaccines — already dished out to 34million people across the UK, or Independent academics have queried the University of Washington team's estimate, saying that they do not look plausible and there is still lots of uncertainty around Omicron data. The researchers did not offer an actual estimate for the IFR of Omicron — which scientists still barely understand given that it was only detected for the first time in mid-November.
The team said: 'Based on the available data, we expect the infection-fatality rate will be per cent lower than for Delta. Studies showed it was twice as deadly as the original virus, which was thought to have an IFR of around 1. But even using that figure would equate to an IFR of around 0. Their own estimates for Omicron — as almost every case will be caused by the strain by January — correspond to an IFR of around 0.
A more detailed report of the final flu season VE estimates is available in an article published in Clinical Infectious Diseases external icon. More information about vaccine effectiveness is available at Vaccine Effectiveness — How well does the flu vaccine work? The current influenza vaccine is recommended because it is the best way to prevent influenza infections. Efforts are underway to improve influenza vaccines. The public health community and the federal government are investing in and supporting the development of new and improved influenza vaccines.
In the meantime, influenza vaccine is the best tool we have to protect as many people as possible against influenza. How well the flu vaccine works or its ability to prevent influenza illness can range widely from season to season and also can vary depending on who is being vaccinated. However, even during years when the vaccine match is very good, the benefits of vaccination will vary across the population, depending on characteristics of the person being vaccinated and even, potentially, which vaccine was used.
Researchers try to determine how well a vaccine works in order to continually assess and confirm the value of influenza vaccines as a public health intervention. Study results about how well a flu vaccine works can vary based on study design, outcome s measured, population studied and the season in which the vaccine was studied. While determining how well a flu vaccine works is challenging, in general, recent studies have supported the conclusion that influenza vaccination benefits public health, especially when the viruses in the vaccine and circulating viruses are well-matched.
Scientists continued to work on better ways to design, conduct and evaluate non-randomized i. CDC has been working with researchers at universities and hospitals since the influenza season to estimate how well influenza vaccine works through observational studies using laboratory-confirmed influenza as the outcome.
These studies currently use laboratory-confirmed medically-attended influenza virus infections as a specific outcome. Similar studies are being done in Australia, Canada and Europe. Antiviral resistance means that a virus has changed in such a way that antiviral drugs have become less effective in treating or preventing illnesses caused by the virus.
Clades containing strains from Peru and a Phylogenetic analysis of the study sequences for viruses from Peru and 2, global HA sequences revealed extensive geographic mixing Figures 1 , 2 ; fully labeled tree in the Technical Appendix Figure. Perhaps the most notable observation from this analysis was the interseasonal extinction of virus clades from Peru in all regions of the country, even in a tropical region where molecularly confirmed year-round influenza transmission has been noted In addition, the phylogeny showed extensive global mixing of H3N2 viruses, with co-circulation of clades from Peru with those from all Northern and Southern Hemisphere regions, including in countries in Latin and North America, Africa, Europe, Central Asia, and East and Southeast Asia.
In one instance, onward transmission of virus was noted after migration from Peru to the United States Figure 2 , section d. Closer examination of the phylogenetic analysis of sequences for viruses from Latin America showed evidence for the presence of weakly supported sublineages consisting predominantly of strains from Peru but also containing strains from Chile and Bolivia Figure 2 ; this finding is indicative of viral traffic between these border-sharing countries.
Analysis of clustering with strains from Ecuador was limited by a paucity of sequences, but evidence of strongly supported clustering with strains from Peru was found Figure 2. In addition, strains from Peru fell into some weakly supported multinational sublineages containing strains from Brazil, Venezuela, Paraguay, Nicaragua, Colombia, Argentina, and Mexico, which suggests H3N2 viral traffic throughout the Americas online Technical Appendix Figure.
Figure 3. Time-scaled maximum clade credibility phylogeny of hemagglutinin sequences for influenza A H3N2 viruses from 4 locations in Peru. Scale bar refers to year of sampling to indicate time Analyzed separately, the maximum clade credibility tree Figure 3 for strains from Peru showed substantial HA diversity each year; many clades co-circulated at each location. The smaller-sized locations of Tumbes, Puerto Maldonado, and Cusco had a wide range of co-circulating clades, similar to those of larger travel hubs, such as Lima Table 2.
This analysis also showed a short time to most common recent ancestor mean 3. A similarly short mean time to most recent common ancestor 1. To determine the phylogeographic structure in the data, we performed phylogeny-trait association tests Table 3. Differences in the observed and expected maximum clade values tentatively suggested that Lima exhibited the least structure i. Our phylogenetic analysis showed that the level of international H3N2 viral traffic was high and that mixing of Peruvian HA sequences with those from multiple regions of the world was rapid and widespread Figures 1 , 2.
These findings support a continuous H3N2 gene flow in and out of Peru rather than a local closed system in which viruses evolve entirely within the country. Mixing of viruses between all study sites in Peru and other countries may also suggest gene flow in and out of Peruvian locations outside the main air-transport hub of Lima.
However, such a conclusion comes with a strong caveat because we may not have sampled all Lima source lineages that seed peripheral locations in the country. Of note, we found evidence of H3N2 virus migration between Peru and its neighbors, although this conclusion was limited by a relative paucity of sequences from these other Latin American countries.
At each study site in Peru, we found multiple co-circulating clades of influenza virus that regularly underwent extinction Figures 1 , 2 , suggesting that much of the genetic diversity of viruses in Peru results from global lineages that pass through the country, rather than from local evolution associated with long-term local persistence.
In particular, all sampled strains, even those from tropical Peruvian sites like Tumbes and Puerto Maldonado, underwent extinction rather than persisted over time, thus regularly halting local evolution of imported influenza viruses.
That the time to most common recent ancestor of the whole sample mean 3. Our findings are consistent with those of studies in countries with temperate regions, such as Australia, New Zealand, and countries in North America, which showed regular introduction of new H3N2 virus lineages and seeding of local seasonal epidemics rather than the interseasonal persistence of lineages 29 — Such studies have similarly revealed that the genetic diversity of seasonal influenza in temperate locales primarily results from the on-going introduction of genetically divergent lineages during seasonal epidemics 5 , 30 — In contrast, interseasonal persistence of H3N2 influenza virus has been documented in subtropical and tropical locations like Hong Kong and Southeast Asia 7 , 8 , A more recent study has shown evidence for multiyear pandemic influenza A H1N1 pdm09 strain persistence in tropical areas of western Africa that are relatively isolated In contrast, an analysis of H3N2 virus persistence over a year period in subtropical China did not demonstrate interseasonal persistence, and the sample size in that study was much larger than that in our study 9.
Our findings did not offer support to a source—sink dynamic within Peru, and they also indicate that Peru is an unlikely common tropical source of persistent lineages that seed other countries in Latin America or the rest of the world. Instead, our findings are more consistent with a shifting metapopulation model of H3N2 virus, such that the virus may pass through any region for a variable amount of time rather than perpetually circulating in fixed locations in the tropics and consistently seeding temperate regions each year 11 , Such a shifting metapopulation model may also explain why some studies show apparent persistence in some tropical and subtropical locations over certain years and others do not 7 — 9 , This model is also compatible with the existence of temporary source populations in locations throughout the world.
Indeed, we provide some phylogenetic evidence that Peru may occasionally, but not consistently, act as a temporary source, spreading virus from Peru to another country, from which onward transmission continues Figure 2 , section d.
H3 virus sequences for viruses from Peru also exhibited some clustering by sampling location, a finding consistent with semilocalized seasonal H3N2 virus epidemics in each region of Peru Figure 3 , although with migration between localities. Such semilocalized epidemics have been observed in other areas These data also provided some evidence for weaker spatial clustering in Lima compared with other localities. This evidence is not surprising because Lima has the largest population and, thus, movement of humans around, in, or out of the city would generally be expected to be greater than in other areas.
In this context it is perhaps surprising that Puerto Maldonado, the least populous site, had a similar strength of spatial clustering. This locality has been characterized by rapid population growth, likely due to widespread mining and associated activities Hence, it is possible that frequent human movement in and out of this location is creating more diffusion of influenza virus.
In addition, the true population of this area may be considerably higher than suggested by official statistics.
These findings have implications for public health practice in Peru and Latin America. For example, they suggest that future novel strains of influenza virus may enter Peru at multiple locations rather than just through its major air-transport hub Lima Moreover, the rapid diffusion of influenza virus throughout Peru, even in the more remote regions, also serves as a potent reminder of how quickly influenza virus can disseminate.
We identified Lima and Puerto Maldonado as possible diffusion hubs for influenza virus; perhaps both cities could be prioritized for heightened influenza surveillance if a novel influenza subtype is introduced into Peru.
Although Peru does not appear to be a global source population for influenza viruses, the diversity and co-circulation of many simultaneous lineages of H3N2 virus in the country means that it should not be overlooked as a potential source for novel pandemic strains, particularly given that there is some evidence of high-risk animal farming practices and low biosecurity in this country Similarly, the rapid, widespread, and unpredictable migration of global strains into Peru and widespread global mixing shown in this study emphasize that vaccine recommendations in either hemisphere need to be based on well distributed, widespread global H3N2 virus sampling from as many sentinel laboratories as possible 6.
His main focus of research is in the molecular and digital epidemiology of communicable diseases, particularly in tropical regions. We thank all participants and households who enrolled in this study, and we thank Sebastian Loli for his assistance.
We gratefully acknowledge the authors and originating and submitting laboratories of the sequences from the Global Initiative on Sharing Avian Influenza Data EpiFlu Database that were used as comparator sequences for this research; accession numbers are listed in online Technical Appendix Table 4. Sequencing was performed by the J. Experts say there is no evidence of onward spread and all close contacts of the person are being monitored.
The individual is currently well and self-isolating, and the risk to the public is very low. Avian flu, also known as bird flu, is a type of influenza that spreads among birds. The UK has recently seen a large number of outbreaks and incidents of the H5N1 strain of avian influenza in birds across the country. Some strains of bird flu can pass from birds to people but, again, is rare and requires close, prolonged contact. Officials say the person in question got the infection from "very close, regular contact with a large number of infected birds, which they kept in and around their home over a prolonged period of time".
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