By mid-June 2021, almost 42% of the US population had been fully vaccinated against Covid-19, with about 52% having received one vaccine dose. In the UK, approximately 78% of the adult population had received one Covid vaccine dose, with about 66% of the population having received both doses of the two-dose vaccine
Compare these vaccination rates to Russia, where only 8% of the population had been vaccinated by the end of April. A recent survey indicates that a staggering 62% of the population do not plan on being vaccinated.
India, where Covid now appears to be raging out of control, had about 13% of its population vaccinated as of mid-May, And had suffered over 412,000 Covid deaths by the end of July.
There has been considerable concern regarding the existing efficacy of the vaccines against newly-evolving SARSCoV- 2 virus variants. Many of these variants have genetic changes enabling them to become more highly infective, with increases in transmissibility or disease severity.
The B.1.1.7 variant, first detected in the UK last December, is now the most common form of SARS-CoV-2 virus circulating in the US. The B.1.617.2 variant, first detected in India last December, has become more prevalent in the UK, where it accounted for a staggering 91% of Covid infections in mid-June.
Both variants appear to be more readily transmissible from person-toperson than the earlier circulating SARS-CoV-2 virus.
Pfizer & AstraZeneca
A recent comparison of Pfizer-BioNTech and Oxford-AstraZeneca vaccines against symptomatic Covid-19 infections from the B.1.1.7 and B.1.617.2 variants showed that two doses of the Pfizer-BioNTech vaccine was 93% effective against symptomatic illness from the B.1.1.7 variant, and 88% effective against the B.1.617.2 variant.
The Oxford-AstraZeneca vaccine was 66% effective against symptomatic illness from the B.1.1.7 variant after two vaccine doses, and 60% effective against the B.1.617.2 variant. Three weeks after a single vaccine dose, both vaccines were 50% effective against symptomatic illness from the B.1.1.7 variant, and 33% effective against the B.1.617.2 variant.
Notably, mixing doses of AstraZeneca and Pfizer vaccine in the UK led to more frequent fevers, chills, and aches in those 50 years or older.
By early March 2021, most Covid cases in Qatar were from B.1.351 and B.1.1.7. For B.1.1.7 SARS-CoV-2 variants, an 89.5% efficacy against Covid infection was observed 14 days after the second vaccine dose. For the B.1.351 SARS-CoV-2 variant, a 75% efficacy against Covid infection was observed 14 days after the second vaccine dose.
Importantly, the Pfizer vaccine protected against severe outcomes from any SARS-CoV-2 variant with a 97.4% efficacy. A recent Pfizer-University of Texas Medical Branch at Galveston study demonstrated that newly-emerged variants B.1.526, B.1.429, B.1.1.7, and neutralising antibody.
Novavax vs B.1.351 variant
A Phase 2 trial conducted in South Africa shows that Novavax vaccine demonstrates a 51% efficacy against symptomatic Covid-19 infection from the B.1.351 variant over a 12-month follow-up period. Prior infection with non-B.1.351 strain did not appear protective against B.1.351 virus during the first two months of follow-up.
Moderna vs B.1.351 variants
A variant strain-matched Covid vaccine booster shot given to fully vaccinated individuals increased neutralising antibodies against B.1.351, when compared to booster doses with the original vaccine.
Vaccination alone not enough?
A recent modelling study of vaccination strategies in the US shows that vaccinations alone cannot stop the spread of Covid-19 and its variants. This study advises that strict social distancing measures remain in place until sufficient population immunity is achieved.
Unfortunately, with the summer weather, many US states no longer require mask-wearing and other social distancing measures, perhaps inviting a Covid resurgence. In the UK donning masks and social distancing will not be required in many situations beyond 19 July. Minimal or no social distancing indoors began in April.
Prior infection with Covid-19
An Italian study showed that once infected with Covid-19, the risk of reinfection is very low. Natural immunity may provide protection for at least one year following initial infection, similar to the protective effects of Covid-19 vaccination.
A recent small (<1,000 subjects) UK study conducted in healthcare workers found that those with prior Covid-19 infection had an increased risk of experiencing an adverse event following their first dose of Pfizer vaccine. Prior infection was associated with greater Covid-19 vaccine symptoms and severity.
Women and younger individuals were more likely to experience adverse events, which commonly included fever, fatigue and myalgia.
Brazil’s Project S
A recent mass vaccination experiment (‘Project S’) took place in Brazil from February to-April 2021, using China’s CoronaVac vaccine. The goal was to assess effectiveness of mass vaccination with CoronaVac on community spread of Covid-19.
CoronaVac had low efficacy in clinical trials with a two-dose average efficacy of 50%. Vaccination was made available to residents of Serrana, a small town of 45,000, at a time when eligibility restrictions in Brazil would have prevented vaccination.
At the beginning of Project S, 5% of residents were infected and nearly 25% had previously been infected. The population was divided into four groups based on their location and community interaction. The town was never isolated or restricted from inter-city travel.
After the first eight weeks, 96% of the first 27,000 eligible residents had received two doses. By the time the third group received the second dose, 75% of the eligible population was vaccinated. As a result, symptomatic cases decreased by 80%, hospitalisation decreased by 86% and deaths fell by 95%.
This study demonstrates that even a vaccine with low efficacy can be used to control Covid-19 spread. Prior infection combined with increased vaccination may have helped to push the town towards herd immunity.
UK BOOSTER TRIALS
Vaccine booster trials have begun in the UK. Seven different vaccines will be included in this study, to be conducted at 16 sites in England. This will be the first trial to accumulate data on a third vaccine dose, and is planned to involve 2,886 patients aged 30 years and older.
This third vaccine dose will be given a minimum of ten to twelve weeks from the second vaccine dose. Along with standard vaccine sideeffect monitoring, blood samples will be collected and tested for immune responses at days 28, 48, 308 and 365.
Vaccines included in this trial are those manufactured by Oxford-Astra- Zeneca, Pfizer-BioNTech, Moderna, Novavax, Valneva, Janssen and Curevac. The initial trial data anticipated in September 2021 should help to inform a vaccine booster programme in the UK.
A recent US CDC study examined ‘breakthrough infections’ of those fully vaccinated (at least two weeks after the second vaccine dose) – and from whom SARS-CoV-2 RNA or antigen can be detected in a respiratory specimen.
From January through April 2021, some 10,262 SARS-CoV-2 vaccine breakthrough infections were identified in the US, out of about 101 million fully vaccinated individuals. Of these infected individuals, 27% were asymptomatic, 10% were hospitalised, and 2% died.
The median age of those who died was 82 years, and 18% of these died from causes unrelated to the disease. Vaccine breakthroughs are expected, and comprise a very small number of Covid-19 cases. From 1 May only those vaccine breakthrough cases resulting in hospitalisation or death were tracked.
Towards a Covid-free future?
While Western nations are slowly inching towards achieving herd immunity through a combination of vaccination, social distancing measures, and recovered Covid-19 cases, many nations continue to struggle. It remains an ongoing effort to manufacture and distribute enough vaccines globally while new SARS-CoV-2 variants continue to evolve among those stricken with this virus. The global fight against this deadly pandemic continues, and the final tally of the role that vaccination has in defeating it has yet to be written.
Col (Ret) Zygmunt F. Dembek is an epidemiologist and biochemist. He has written extensively on biodefence and has conducted pandemic preparedness exercises worldwide.
Soldiers from the Ohio National Guard reach a milestone: administering their 100,000th dose of Covid-19 vaccine at Wolstein Community Vaccination Center in Cleveland, Ohio.
©US Department of Defense