The number of Covid-19 cases in Switzerland continues to fall. On 15 June 2021, 243 new cases were reported. A month earlier the 7-day average was 2,161 cases. Swiss cases have dropped by 89% in a month.
In the UK the number of cases has roughly tripled over the same period and the government has decided to extend current restrictions until 19 July 2021.
Why is there such a large difference in the number of new Covid-19 cases between the two countries?
The first difference is Covid-19 variants. In the UK the Delta variant, which first emerged in India, makes up more than 90% of new cases.
Tim Spector, who manages the large Zoe database of Covid-19 data in the UK says recent estimates suggest that the Delta variant is twice as contagious as the original variant and has an R0 of 6, which means an average infected person infects 6 others.
In the UK, much of the recent rise in cases is among the unvaccinated and younger age groups, with the infection rate among 20-29 year olds more than doubling in a week. And while the risk of death for this group is low (<0.1%), an average 29-year old man with no underlying health conditions has a 2.7% chance of needing hospital treatment. There is also evidence that suggests the risk of hospitalisation is higher with the Delta variant.
Prof Spector also points out the relatively high risk of long Covid in this age group. Research recently presented by the NY Times suggests that 19% of initially asymptomatic patients, who are often young, have long Covid symptoms.
In addition, there is the risk of spread. Someone with mild symptoms may be have a low risk of dying, however, they could infect someone more vulnerable.
The Delta variant (B.1.617.2) was first detected in Switzerland in April 2021. Between then and the week beginning 7 June 2021, around 100 cases have been detected, according to data presented by covSPECTRUM, a research project set up by FOPH and ETHZ. It is estimated that the Delta variant accounts for a rising percentage of cases in Switzerland. In the week beginning 7 June 2021, the variant made up 21% of the samples sequenced, up from 3.5% the week before.
A chart by covSPECTRUM, that compares the rise of the Delta variant in Switzerland to the other nations, shows how quickly the variant can progress as a percentage of cases.
In the UK, the Delta variant went from for 25% to 93% of cases in 5 weeks (see chart above). However, whether (or when) the Delta variant will take hold in Switzerland and become dominant like it has in the UK and India remains to be seen.
In any case, the relatively low prevalence of the Delta variant in Switzerland to date is likely to explain much of the difference in new case numbers between the UK and Switzerland.
Vaccination rates and doses
The UK data suggest second vaccine doses are important for the Delta variant. Rising cases in the 50-59 year old age band, among which many have had one dose but not two, combined with a more muted rise among those 60 and over, who have mainly had two shots, suggest that the second shot boosts protection against the Delta variant. Research backs up this observation.
A combination of relatively low vaccination rates and even lower numbers of people who have had two doses in the 20-29 age group might explain why cases are growing so fast in the UK. Given that Swiss vaccination rates for this age group are similar, if the Delta variant gets away, Switzerland’s new case data might start to resemble the UK’s.
The two nations are using different vaccines. Switzerland is using only the Pfizer and Moderna mRNA vaccines. The UK has been using these two plus the AstraZeneca vaccine, which accounts for around 60% of its total vaccinations.
And while the efficacy of the Pfizer and AstraZeneca vaccines seems to be similar against the Delta variant after one dose (33%), it varies after the second dose. After the second dose the Pfizer vaccine is 88% effective compared to 60% for the AstraZeneca vaccine, based on research by Public Health England. The study did not cover the Moderna vaccine.
It is hoped that even if vaccines are less effective against preventing cases of the Delta variant they will cut fatality rates. Data from Public Health England suggests that a single dose of vaccine reduces the chances of needing hospital treatment by roughly 75%, despite the high levels of Delta circulating there.
Different symptoms with Delta
Prof Spector reports that Covid-19 symptoms appear to be changing. Symptoms from the Delta variant are now more likely to resemble a cold. The widely reported loss of smell associated with earlier variants doesn’t make the top 10 most common symptoms now said Spector. Since the beginning of May 2021, the top UK symptoms have been headache, sore throat, runny nose and fever, he said.
Avoiding a resurgence in Switzerland
It is likely that the main difference between the number of new cases in Switzerland and the UK is down to differences in the prevalence of the Delta variant. Switzerland’s best chance of avoiding a resurgence of Covid-19 cases like in the UK appears to hinge on vaccination and containing this variant. In addition, the more infectious a disease is the higher the vaccination rate needs to be to halt spread.
Switzerland may have a vaccine advantage against new variants due to its decision to only use the two mRNA vaccines, but this only materialises when people are vaccinated, not once but twice. On this metric Switzerland is currently far behind the UK with 27% versus 45% of the population fully vaccinated.