果冻影院

听鈥淛ust when I鈥檝e begun to get myself together, you waltz right in the door, just like you鈥檝e done before鈥︹�澨� These words by Dolly Parton, the patron of the Moderna vaccine, are apt for this stage of the pandemic. As the UK government rides high in the polls, vaccination rates increase and case rates plummet, the British believe they have got themselves together. We remain, though, in a global battle with this microscopic monster. Every day we read about new variants, new surges and new crises overseas, all threatening to waltz right in the door.

There remain good reasons for optimism. Figures from 12 May showed that in the UK, out of a population of 68 million there were 106 daily hospitalisations and only 11 deaths within 28 days of a positive test. As of 12 May, 35.7 million people (68 per cent of the adult population) had received a first vaccine dose, while 18 million had received two. This puts the country close to the original estimate of coverage required to achieve herd immunity.

Does immunity last? Laboratory evidence shows considerable variability in an individual鈥檚 immune response. While certain classes of antibodies fade quickly, protection persists for at least eight months in many people and residual T cell protection may last much longer. Even in the case of new 鈥渆scape鈥� variants of Covid-19, there is no evidence to suggest that vaccines will fail to protect against serious disease or death.

However, there is also cause for concern. As Boris Johnson鈥檚 plan for unlocking in England approaches stage three on 17 May, and many voices in the media clamour for faster progress, positive case rates are stuck at over 2,250 per day 鈥� three times the case level in the UK in early July 2020. The virus is still in circulation.

Still more worrying are the new variants from India, which are rapidly replacing our own. In India, variant B1.617 has quickly taken over from the Kent variant B.1.1.7. In the UK, B.1.617 is now a 鈥渧ariant of concern鈥�, with cases doubling every week (particularly the sub-lineage B1.617.2). Scientists are trying to establish whether this variant increases transmission rates, as the Kent variant did in November 2020 when it caused chaos in the NHS and around 70,000 deaths. If the transmission rate of B.1.617.2 is higher, Sage modelling suggests that even with complete vaccine protection, we could see many thousands of new hospital admissions.听

But if variants do have mutations that escape much of the vaccine-induced immune response, surely our clever scientists can quickly re-engineer the vaccine? We certainly do this for influenza annually. Nonetheless, there is another concern. Booster vaccines sometimes don鈥檛 work because of the phenomenon of 鈥渙riginal antigenic sin鈥�. This is where new variants of a virus preferentially boost the antibody response against the original strain, meaning the effectiveness of the response induced by vaccination falls 鈥� an effect observed with influenza.

Vaccination rates are also likely to slow as the roll-out reaches younger age groups, especially those in ethnic minorities. We could still end up with millions of people unprotected. And as the transmissibility of new variants rise, the population coverage of vaccination required to achieve herd immunity becomes prohibitively high. New variants might also prolong the period of infectiousness, which heightens the need to isolate cases and their contacts rapidly and keep them isolated for long enough to prevent transmission. But the UK鈥檚 test, trace and isolate system remains overcentralised and inadequate. Median turnaround times for home tests are 39 hours and for satellite tests 32 hours.

The number of cases transferred to the contact tracing system has been falling since early January 2021. Britain鈥檚 outsourced contact tracing, which monopolises investment, is far inferior to local public health teams. Since Test and Trace launched, 98 per cent of all contacts managed by local health protection teams have been successfully reached. But in the last week of April 2021, only 60 per cent of cases were reached by call centres within three days of taking a Covid-19 test. Only 76 per cent of contacts from a different household were identified and told to self-isolate.

We don鈥檛 have real-time information on how many people actually isolate 鈥� the critical performance indicator. In the absence of adequate financial support for low-income families, there is little incentive for them to take a test or isolate.

Despite these caveats, the odds are still in our favour. Immunisation should protect most vulnerable adults from serious illness, even from escape variants of Covid-19. Viruses are only concerned with their own survival. Mutant variants that might do a better job at reproduction win out by natural selection. Whether the virus kills its host is largely immaterial. We must hope that the pandemic ultimately ends with a variant that transmits beautifully but causes little more than a cold.

Until then, we still face the prospect of surges, border controls 鈥� and, in the absence of a local, rapid and efficient contact tracing and quarantine system, further lockdowns.

This article was first published in听听on 14 May 2021.

Links

• Original article in听
• 果冻影院 Institute for Global Health
• 果冻影院 Faculty of Population Health Sciences