How do Covid-19 vaccines work?

Vaccines generally imitate parts of the virus they protect against, prompting a response from the immune system.

The Covid-19 vaccines that have emerged over time use several approaches to reach that outcome.

The vaccines from Moderna and Pfizer use a new technology. The vaccines deliver messenger RNA, or mRNA, which is a genetic recipe for making the spikes that sit atop the coronavirus, reports CNN Health.

AstraZeneca's vaccine, developed with a team at Britain's Oxford University, is called a vector vaccine. It uses a common cold virus called an “adenovirus” to carry the spike protein from the coronavirus into cells.

Johnson & Johnson's vaccine and Russia's Sputnik V use a similar approach.

Pfizer/BioNTech

Pfizer and its German-based partner, BioNTech, use a new approach to making vaccines that uses messenger RNA or mRNA.

This design was chosen for a pandemic vaccine years ago because it's one that lends itself to quick turnaround. All that is needed is the genetic sequence of the virus causing the pandemic. Vaccine makers don't even need the virus but just its sequence.

The researchers used a piece of genetic material coding for a piece of the spike protein – the structure that adorns the surface of the coronavirus, giving it that studded appearance.

Clinical trials showed Pfizer's vaccine was 95% effective in preventing symptomatic infections. Pfizer is working to show the vaccine can prevent all infections, including those that don't cause symptoms.

MRNA is very fragile so it's encased in lipid nanoparticles – a coating of a buttery substance that can melt at room temperature. That's why Pfizer's vaccine must be kept at ultracold temperatures of -75°C. That means special equipment is needed to transport and store this vaccine.

Moderna

Moderna's vaccine is also based on mRNA. "mRNA is like software for the cell" Moderna said on its website.

Like Pfizer's vaccine, the Moderna vaccine goes into the muscle cells of the arm, and perhaps to nearby immune system cells, and instructs them to make pieces of spike protein.

Moderna’s vaccine showed 94% effectiveness.

Moderna has come up with a different formulation for the lipid nanoparticles to protect the mRNA in its vaccine.

These formulations are corporate secrets, but Moderna thinks its approach is better and said its vaccine can be shipped at minus -20°C and can be kept stable for 30 days at 2°C to 8°C, the temperature of a standard home refrigerator.

AstraZeneca

AstraZeneca's vaccine, made with a team at Britain's Oxford University, is called a vector vaccine. It uses a common cold virus called an adenovirus to carry the spike protein from the coronavirus into cells.

It also aims to make people's bodies produce their own vaccines by churning out little copies of spike protein, but the delivery method is different.

The company has pledged to make its vaccine available inexpensively to countries around the world. The vaccine can be kept stable for six months at standard refrigerator temperatures, the company said.

Confusing data from trials indicated AstraZeneca's vaccine could be 70% effective on average, reports CNN.

Serum Institute of India, the largest vaccine manufacturer, is producing the vaccine in huge quantities. Bangladesh is primarily planning to administer 30m doses of this vaccine.

Johnson & Johnson's vaccine

Janssen's coronavirus vaccine, the vaccine arm of Johnson & Johnson's, has made a recombinant vector vaccine. It uses a genetically engineered version of adenovirus 26, which can cause the common cold but the gene tinkering has disabled it. It also delivers the genetic instructions to make a piece of spike protein.

This is one vaccine that has been tested on the market before. The adenovirus 26 vector was used to make the company's Ebola vaccine, which won marketing authorization from the European Commission in July.

It's a one-shot vaccine and trials showed side-effects were minimal.

Novavax

Maryland-based biotechnology company Novavax specializes in "protein subunit" vaccines. They use virus-like nanoparticles as a base and cover them with genetically engineered pieces of the coronavirus spike protein.

This is also a tried and true vaccine approach. A hepatitis B vaccine given to newborns is a protein subunit vaccine, as is the human papillomavirus or HPV vaccine and FluBlok, Sanofi's influenza vaccine.

Also Read - OP-ED: Covid-19 vaccines: What we know so far

Novavax uses an insect virus called a baculovirus to get the coronavirus spike protein into moth cells, which then produce the protein. This is harvested and mixed with an adjuvant – an immune booster – based on saponin, found in soap bark trees.

Sanofi and GlaxoSmithKline

This is also a protein subunit vaccine, using Sanofi's FluBlok technology with a GlaxoSmithKline adjuvant. It also uses a baculovirus to grow little bits of spike protein.

Phase 1/2 trials showed the vaccine elicits an immune response comparable to patients who recovered from Covid-19 in younger adults, but the vaccine did not produce the desired immune response in older adults. The companies plan to launch a new trial in February.

Sinovac and Sinopharm

Chinese company Sinovac's CoronaVac uses an inactivated virus – one of the oldest methods for vaccinating people. Whole batches of coronavirus are grown, "killed" and then made into vaccines. Likewise, Sinopharm's vaccine is an inactivated virus.

Sputnik V

Russia's Sputnik V coronavirus vaccine is an adenoviral vector vaccine. It uses two common cold viruses called adenovirus 5 and adenovirus 26 to carry the genetic material for the spike protein into the body.