Covid cases occur after short periods of immunity and people could find themselves re-infected for just 28 days due to the rapidly evolving Omicron variant, scientists have warned.
Omicron caused shorter, sharper waves of infections across the UK, with study app ZOE Covid measuring a peak of around 350,000 cases a day earlier this month, before cases declined nearly halved over the next two weeks.
However, rather than bringing an extended period of immunity within the population, scientists warn of the ability of the BA.4 and BA.5 subvariants to escape accumulated resistance from previous infections. , which means people could see themselves catching Covid again in just a few weeks. .
Official UK government figures have dropped significantly since the end of free mass Covid testing in April, but the data still shows a shorter gap between the peak of each respective Covid wave since March 2020.
After the Alpha variant’s peak of 352,000 weekly infections in January 2021, it took more than six months for the Delta wave to reach a peak of 303,000 cases per week last July.
However, since the first wave of Omicron saw official government figures hit an all-time high of over one million cases per week at the end of December 2021, there have been three subsequent peaks of Omicron in just seven months.
This is a trend that has already been recognized in countries like Australia and New Zealand and in some US states.
In Australia, health experts have raised concerns about Covid reinfections and recently recommended that official guidelines on the post-infection immunity period be shortened by just 12 weeks, meaning people should get tested and self-isolate if they show symptoms more than four weeks after recovery.
Western Australia health officer Andy Robertson said: ‘BA.4 and BA.5 make up a growing percentage of our cases, reaching over 60% of cases last week.
“This means people who have had Covid-19 should get tested again and self-isolate if they have symptoms more than 28 days after recovering from Covid-19.”
The high levels of reinfection are partly the product of Omicron, which has the ability to evade immunity unlike previous variants of Covid-19, and experts believe the UK is now experiencing similar trends.
Professor Azeem Majeed, head of primary care and public health at Imperial College London, said I“We have seen a shortening of the gaps between Covid-19 waves in the UK since the emergence of Omicron and its sub-variants.
“Omicron appears to have a greater ability to evade immunity from vaccination and previous infection. This leads to more people being re-infected and sometimes a fairly short interval between infections.”
The short gap has also meant that newer Omicron subvariants quickly supplant older ones.
The original Omicron variant, BA. 1, lasted about a month and a half before being overtaken by Omicron’s second variant, BA. 2 in the UK which has now been overtaken by a newer variant, BA. 5. In contrast, Delta was the dominant variant in England for over 200 days.
A vaccine that better targets the Omicron variant may better offer the possibility of protection against the variant and its subvariants. Earlier this week, Pfizer announced that they had started a mid-stage study of a modified Covid-19 vaccine that targeted both the original as well as the BA 2 Omicron subvariant.
In July, the Food and Drug Administration recommended that Pfizer and Moderna move forward with the development of Omicron-specific boosters. The FDA noted that these injections will hopefully be ready for use by mid-fall.
It is currently unclear whether the UK will offer an updated vaccine for the autumn booster programme.
As Covid has developed the age distribution of cases has also changed significantly, with people over 60 now accounting for the largest share of Covid-19 infections in England, for the first time since the original variant in early 2020.
While the first Omicron variant, BA. 1, was widely seen in people under 19, this has now changed significantly, with people under 19 now accounting for the smallest share of new infections compared to other age groups.
The cases of the Omicron BA 2 and BA 5 subvariants represent the first time that people under the age of 19 accounted for the smallest share of infections. During all other Covid variants except the very beginning of the original strain, young people dominated the spread of the disease.
In part, the waves of Covid are also getting shorter because, despite Omicron’s ability to break immunity, immunity continues to rise in the UK through both infection and vaccination. This means that new variants are removed in a way that previous ones were not.
Prof Beate Kampmann, Professor of Pediatric Infection and Immunity; and director of the Vaccine Centre, London School of Hygiene and Tropical Medicine, said I: “Immunity against SARS-Cov2 is increasing in the population due to both previous infection or vaccination.
“Therefore, infections with new variants are also going to be at least partially suppressed by community and individual immunity, and waves of new variants will not last as long unless there is a very substantial change. in the composition of the virus. We don’t see that level of immune evasion.
However, as Professor Kampmann notes, it is not a foregone conclusion that the waves of Covid will become less severe and this is based on the assumption that immunity remains strong, which itself is based on the fact that there are no significant changes in the composition of the virus.
So far this has been the case and there is certainly reason to hope that with a series of fall boosters targeted at Omicron this trend will continue, although this is by no means guaranteed.
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