Meanwhile, the continent saw 248,000 new confirmed cases over the past week, with at least 24 countries seeing a surge in infections driven by the delta variant.
"This is a preventable tragedy if African countries can get fair access to the vaccines," Matshidiso Moeti told reporters.
The WHO Africa director said 13 million doses were administered in the past week, three times more than the number of shots given in the previous week as donations of doses increased from developed countries. But that remains a drop in an ocean on the continent home to 1.3 billion people, where the Africa CDC says only 2.4% are currently vaccinated.
Africa's brutal resurgence driven by the delta variant is further stretching already strained health systems across the continent. As African countries struggle, the United States and other high-income countries are talking about booster shots.
A COVID-19 vaccine is a vaccine intended to provide acquired immunity against severe acute respiratory syndrome coronavirus 2 , the virus that causes coronavirus disease 2019 . Prior to the COVID-19 pandemic, an established body of knowledge existed about the structure and function of coronaviruses causing diseases like severe acute respiratory syndrome and Middle East respiratory syndrome . This knowledge accelerated the development of various vaccine platforms during early 2020. The initial focus of SARS-CoV-2 vaccines was on preventing symptomatic, often severe illness. On 10 January 2020, the SARS-CoV-2 genetic sequence data was shared through GISAID, and by 19 March, the global pharmaceutical industry announced a major commitment to address COVID-19. The COVID-19 vaccines are widely credited for their role in reducing the spread, severity, and death caused by COVID-19.
Many countries have implemented phased distribution plans that prioritize those at highest risk of complications, such as the elderly, and those at high risk of exposure and transmission, such as healthcare workers. Single dose interim use is under consideration to extend vaccination to as many people as possible until vaccine availability improves.
As of 10 September 2021, 5.66 billion doses of COVID-19 vaccine have been administered worldwide based on official reports from national public health agencies. AstraZeneca anticipates producing 3 billion doses in 2021, Pfizer–BioNTech 1.3 billion doses, and Sputnik V, Sinopharm, Sinovac, and Janssen 1 billion doses each. Moderna targets producing 600 million doses and Convidecia 500 million doses in 2021. By December 2020, more than 10 billion vaccine doses had been preordered by countries, with about half of the doses purchased by high-income countries comprising 14% of the world's population.
At least nine different technology platforms are under research and development to create an effective vaccine against COVID-19. Most of the platforms of vaccine candidates in clinical trials are focused on the coronavirus spike protein and its variants as the primary antigen of COVID-19 infection. Platforms being developed in 2020 involved nucleic acid technologies , non-replicating viral vectors, peptides, recombinant proteins, live attenuated viruses, and inactivated viruses.
Many vaccine technologies being developed for COVID-19 are not like vaccines already in use to prevent influenza, but rather are using 'next-generation' strategies for precise targeting of COVID-19 infection mechanisms. Several of the synthetic vaccines use a 2P mutation to lock the spike protein into its prefusion configuration, stimulating an adaptive immune response to the virus before it attaches to a human cell. Vaccine platforms in development may improve flexibility for antigen manipulation, and effectiveness for targeting mechanisms of COVID-19 infection in susceptible population subgroups, such as healthcare workers, the elderly, children, pregnant women, and people with weakened immune systems.
Several COVID-19 vaccines, including the Pfizer–BioNTech and Moderna vaccines, have been developed to use RNA to stimulate an immune response. When introduced into human tissue, the RNA contained in the vaccine acts as messenger RNA to cause cells to build the SARS-CoV-2 spike protein. This teaches the body how to identify and destroy the corresponding pathogen. RNA vaccines often, but not always, use nucleoside-modified messenger RNA. The delivery of mRNA is achieved by a coformulation of the molecule into lipid nanoparticles which protect the RNA strands and help their absorption into the cells. RNA vaccines were the first COVID-19 vaccines to be authorized in the United Kingdom, the United States and the European Union. Authorized vaccines of this type are the Pfizer–BioNTech and Moderna vaccines. The CVnCoV RNA vaccine from CureVac failed in clinical trails.
Severe allergic reactions are rare. In December 2020, 1,893,360 first doses of Pfizer–BioNTech COVID-19 vaccine administration resulted in 175 cases of severe allergic reaction, of which 21 were anaphylaxis. For 4,041,396 Moderna COVID-19 vaccine dose administrations in December 2020 and January 2021, only ten cases of anaphylaxis were reported. The lipid nanoparticles were most likely responsible for the allergic reactions.
Adenovirus vector vaccines
These vaccines are examples of non-replicating viral vector vaccines, using an adenovirus shell containing DNA that encodes a SARS-CoV-2 protein. The viral vector-based vaccines against COVID-19 are non-replicating, meaning that they do not make new virus particles, but rather produce only the antigen which elicits a systemic immune response. Authorized vaccines of this type are the Oxford–AstraZeneca COVID-19 vaccine, the Sputnik V COVID-19 vaccine, Convidecia, and the Janssen COVID-19 vaccine.
Convidecia and the Janssen COVID-19 vaccine are both one-shot vaccines which offer less complicated logistics and can be stored under ordinary refrigeration for several months.
Sputnik V uses Ad26 for its first dose, which is the same as Janssen's only dose, and Ad5 for the second dose, which is the same as Convidecia's only dose.
Additional types of vaccines that are in clinical trials include virus-like particle vaccines, multiple DNA plasmid vaccines, at least two lentivirus vector vaccines, a conjugate vaccine, and a vesicular stomatitis virus displaying the SARS-CoV-2 spike protein.
Scientists investigated whether existing vaccines for unrelated conditions could prime the immune system and lessen the severity of COVID-19 infection. There is experimental evidence that the BCG vaccine for tuberculosis has non-specific effects on the immune system, but no evidence that this vaccine is effective against COVID-19.