After a period of relative calm this year in the UK, Covid-19 cases surged again in the last two weeks of May, possibly related to the spread of the Delta variant (B.1.617.2) of the virus. This variant, which originated in India, is spreading rapidly and is the most dominant variant in some regions of the UK. The variant is 50% more transmissible than the Alpha variant (B.1.1.7), which had previously been the dominant variant in the country. This surge in cases has not yet increased hospitalisations and deaths, but this could change if the spike in cases is not controlled quickly. The UK’s strategy of fully reopening the country on 21 June would not be viable if hospitalisation and death rates start to rise.
The Alpha variant was the dominant variant of concern in the UK before the introduction of the Delta variant. Vaccines are very effective against the Alpha variant, which encouraged the UK’s roadmap of fully reopening the economy by June. In May, however, the proportion of cases with this variant declined while those with the Delta variant increased rapidly, as shown in Figure 1. The Delta variant is expected to become the dominant variant in June, based on its increasing dominance in the daily genomic sequences of cases.
Public Health England has reported that the Delta variant is 50% more transmissible than the alpha as well as being more virulent, which increases the risk of hospitalisation. This variant is also more resistant to a single dose of the Oxford/AstraZeneca vaccine than Alpha, but two doses are effective against symptomatic cases and hospitalisations. According to recent data from the UK on the Delta variant, 5% of all hospitalisations with the variant had been fully vaccinated, whereas 75% were unvaccinated and 20% had been partially vaccinated.
The UK will likely postpone the lifting of all restrictions on 21 June and implement regional lockdowns to control the rise in cases. As of writing, 40% of the UK’s population has been vaccinated with two doses, which should provide some protection against this ‘variant of concern’. This still leaves most of the population vulnerable to the infection, however. The best course of action is to get the vaccines to as many people as quickly as possible. Mitigation measures to control the numbers of new cases will need to continue until most of the population has been vaccinated.