Efficacy of the AstraZeneca-Oxford University vaccine: A preprint for The Lancet

‘A study (preprint for The Lancet) of data from the Phase 3 clinical trials of the AstraZeneca-Oxford University vaccine evaluated vaccine efficacy after a single dose and for alternate timing for the booster dose. Notably, the UK adapted the timing for the booster dose from 4 weeks after the first dose—which is how the vaccine was designed to be administered and the timing used for clinical trials—to 12 weeks in an effort to provide the first dose to as many people as possible. This study assessed the vaccine’s efficacy in participants who received the 2 doses between 4 and 12 weeks apart.

‘The researchers found that the efficacy after the first dose did not wane in the first 12 weeks. A single dose of the vaccine was 76% efficacious in preventing symptomatic COVID-19 disease in the first 90 days after vaccination, although it was associated with a substantial decrease in efficacy with respect to preventing asymptomatic infection. Notably, however, the additional asymptomatic infections could potentially be among participants who would have otherwise developed COVID-19 symptoms. Additionally, the efficacy in preventing symptomatic disease was higher in participants who received the booster dose later than in those who received it earlier. Vaccine efficacy was 82.4% among participants who received their booster dose 12 weeks or longer after the first dose, compared to 54.9% in those who received their 2 doses less than 6 weeks apart. These results provide support for vaccination plans that delay the booster dose beyond the intended 4 weeks, considering that the immunity conferred after the first dose appears to be relatively stable over the first several months and the overall protection appears to increase with an increased time between the prime and booster doses.

‘The researchers also found that vaccination was associated with an overall reduced risk of infection—54.9% efficacy for 2 doses and 67% efficacy for 1 dose—which provides evidence that the vaccine could also provide protection against SARS-CoV-2 transmission. The role of SARS-CoV-2 vaccines in mitigating transmission risk remains uncertain, but these findings provide a promising indication that vaccination could reduce community spread of the virus, which would be a major tool to bring the pandemic under control.’

**The above summary was contained in an update of Feb 5, 2021, on the COVID-19 pandemic from the Johns Hopkins Center for Health Security 

• Single dose administration, and the influence of the timing of the booster dose on immunogenicity and efficacy of ChAdOx1 nCoV-19 (AZD1222) vaccine

Read here (The Lancet, Feb 1, 2021)

Covid-19: Novavax vaccine shows 89% efficacy in UK trials

‘A new coronavirus vaccine has been shown to be 89.3% effective in large-scale UK trials. The Novavax jab is the first to show in trials that it is effective against the new virus variant found in the UK, the BBC's medical editor Fergus Walsh said. The PM welcomed the "good news" and said the UK's medicines regulator would now assess the vaccine.’

Read here (BBC, Jan 29, 2021) 

Why it takes 2 shots to make mRNA vaccines do their antibody-creating best – and what the data shows on delaying the booster dose

‘With current vaccine shortages, and problems with setting up the infrastructure to vaccinate millions of people, many physicians are concerned that the second dose of vaccine won’t be delivered in the prescribed three-to-four-week window.

‘That booster shot is necessary for the T-cells to stimulate the memory B-cells to produce massive quantities of antibodies. If the booster isn’t given within the appropriate window, lower quantities of antibodies will be produced that may not provide as powerful protection from the virus.’

Read here (The Conversation, Jan 29, 2021)

Just like Pfizer, China says vaccines can beat new strains

‘Virologists and vaccine specialists with China’s National Health Commission (NHC) said on Wednesday they had a detailed plan to upgrade homegrown vaccines against Covid-19 to “version 2.0” within two months to stop the spread of new mutant strains found across the United Kingdom and South Africa.

‘The claim coincided with Pfizer’s announcement on Wednesday that its Covid-19 vaccine works against mutated variants found in the UK and South Africa, according to a lab study. China’s claim comes as local firms SinoPharm and Sinovac crank out their Covid-19 shots for mass inoculations.’

Read here (Asia Times, Jan 28, 2021)

Emerging coronavirus variants may pose challenges to vaccines

‘The mRNA technology on which the Pfizer and Moderna vaccines rely can be altered in a matter of weeks, and far more easily than the process used to produce flu vaccines. But it would be wise to prepare for this eventuality [a time when the current slew of vaccines become less effective] now and think through not just the technical aspects of updating the vaccines, but the testing, approval and rollout of those vaccines, experts said.

‘Still, the best path forward is to prevent the emergence of new mutations and variants altogether, they said. "Imagine having to do catch-up like this all the time - it's not something desirable," Dr Iwasaki said. "If we can just stop the spread as soon as possible, while the vaccine is very effective, that's the best way."

Read here (New York Times/Straits Times, Jan 22, 2021)

Three questions and the emerging answers about Covid-19 vaccine protection

‘As the COVID-19 vaccine rolls out, three big questions loom. First, can someone who has been vaccinated still spread the disease? Second, will the vaccine remain effective as the virus itself evolves? And third, how long will the vaccine's protection last?

‘Answers to these questions lie in our immune systems. And the answers aren't straightforward because our immune systems are both remarkably adept and remarkably challenging to predict.’

Read here (NPR, Jan 18, 2021)

There are four types of Covid-19 vaccines: Here’s how they work

‘The fight against COVID-19 has seen vaccine development move at record speed, with more than 170 different vaccines in trials. But how are they different from each other and how will they protect us against the disease?

‘There are more vaccine candidates simultaneously in the pipeline for COVID-19 than ever before for an infectious disease. All of them are trying to achieve the same thing – immunity to the virus, and some might also be able to stop transmission. They do so by stimulating an immune response to an antigen, a molecule found on the virus. In the case of COVID-19, the antigen is typically the characteristic spike protein found on the surface of the virus, which it normally uses to help it invade human cells.

‘The four main types of Covid-19 vaccines: There are four categories of vaccines in clinical trials: (1) Whole virus, (2) Protein subunit, (3) Viral vector and (4) Nucleic acid (RNA and DNA). Some of them try to smuggle the antigen into the body, others use the body’s own cells to make the viral antigen.’

Read here (Gavi, as Jan 2021)

Watch here (Gavi, Youtube, as Jan 2021)

Safety and efficacy of the BNT162b2 mRNA Covid-19 vaccine (Pfizer clinical trial)

BACKGROUND: ‘Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and the resulting coronavirus disease 2019 (Covid-19) have afflicted tens of millions of people in a worldwide pandemic. Safe and effective vaccines are needed urgently.’

METHODS: ‘In an ongoing multinational, placebo-controlled, observer-blinded, pivotal efficacy trial, we randomly assigned persons 16 years of age or older in a 1:1 ratio to receive two doses, 21 days apart, of either placebo or the BNT162b2 vaccine candidate (30 μg per dose). BNT162b2 is a lipid nanoparticle–formulated, nucleoside-modified RNA vaccine that encodes a prefusion stabilized, membrane-anchored SARS-CoV-2 full-length spike protein. The primary end points were efficacy of the vaccine against laboratory-confirmed Covid-19 and safety.’

RESULTS: ‘A total of 43,548 participants underwent randomization, of whom 43,448 received injections: 21,720 with BNT162b2 and 21,728 with placebo. There were 8 cases of Covid-19 with onset at least 7 days after the second dose among participants assigned to receive BNT162b2 and 162 cases among those assigned to placebo; BNT162b2 was 95% effective in preventing Covid-19 (95% credible interval, 90.3 to 97.6). Similar vaccine efficacy (generally 90 to 100%) was observed across subgroups defined by age, sex, race, ethnicity, baseline body-mass index, and the presence of coexisting conditions. Among 10 cases of severe Covid-19 with onset after the first dose, 9 occurred in placebo recipients and 1 in a BNT162b2 recipient. The safety profile of BNT162b2 was characterized by short-term, mild-to-moderate pain at the injection site, fatigue, and headache. The incidence of serious adverse events was low and was similar in the vaccine and placebo groups.’

CONCLUSIONS: ‘A two-dose regimen of BNT162b2 conferred 95% protection against Covid-19 in persons 16 years of age or older. Safety over a median of 2 months was similar to that of other viral vaccines. (Funded by BioNTech and Pfizer; ClinicalTrials.gov number, NCT04368728. opens in new tab.)’

Read here (New England Journal of Medicine, Dec 31. 2020)