COVID-19 Vaccines: How Do They Differ?

by Charles Marcus P. Matanguihan (Hachimoji)

As the spread of COVID-19 has persisted for more than a year now, the development of vaccines provides hope in ending the pandemic as they reduce the risk of infection and severity of symptoms. Vaccines train the immune system to recognize an antigen, particularly the spike protein of SARS-CoV-2, which plays a vital role in penetrating human cells and causing disease. As of writing, four main types of COVID-19 vaccines have been approved or are now undergoing clinical development and approval.

Whole virus vaccines utilize weakened or inactivated viruses to trigger immune responses without causing illness. Scientists mainly use chemicals, heat or radiation to modify the virus and develop this type of vaccine. Known examples include the approved Sinovac’s CoronaVac and the unapproved Sinopharm. There is 93% and 100% prevention of hospitalization and death respectively in Sinopharm’s Abu Dhabi studies.

In preventing symptomatic COVID-19 through CoronaVac, interim data from trials show 91.25% efficacy among a subgroup of 1322 participants in a trial involving 7371 people. However, researchers in Brazil announced in January that the CoronaVac was 78% effective in preventing mild cases, as presented from a phase III trial that involves 12 000 healthcare workers in the country. A week after the announcement, another data emerged after taking into account the very mild cases: the vaccine was only 50.4% effective against symptomatic COVID-19 patients, while trials in Indonesia show 65% effectiveness.

Protein subunit vaccines, on the contrary, only contain purified fragments of a virus like the spike proteins. However, they often require adjuvants and booster shots to enhance the weak immune response promoted by the antigen and are relatively complex to manufacture. Novavax is a protein subunit vaccine which aims to be approved by the second quarter of this year. It is reported that Novavax induced a 100% prevention of hospitalization and death in its United Kingdom and South Africa trials. Also, UK trials show the vaccine’s 89.3% efficacy against mild disease.

Viral vector vaccines use harmless modified viruses that can deliver a genetic sequence to human cells. This sequence then codes for SARS-CoV-2 spike proteins and promotes an immune response. Oxford-AstraZeneca, Sputnik V, and Johnson & Johnson are currently the only viral vector vaccines approved for use by the Philippine Food and Drug Administration (FDA). Oxford-Astrazeneca and Johnson & Johnson (J&J) induced a 100% prevention from hospitalization and death in their United States trials. Oxford-Astrazeneca also prevents 75% of mild to moderate disease, as reported by the trials in South Africa before the spread of the new variant. However, the resurgence of the B.1.351 variant, also known as the South African variant lowers the efficacy of the vaccines in preventing mild to moderate cases. The Oxford-Astrazeneca vaccine prevents only 21.9% of moderate to mild disease. On the other hand, as there are reported cases of hospitalization and death after the injection of Sputnik V, it was found out that these cases have no association with the said vaccination. 

mRNA vaccines are made of synthetic mRNA that only code for harmless antigens found in the virus. This type has a similar mechanism with viral vector vaccines but instead of viruses, lipid nanoparticles are used as a delivery system since it can protect the genetic material from enzymatic degradation and easily diffuse into the cell membrane. Known examples are Pfizer-BioNTech and Moderna which have highest efficacy at around 95% and also resulted in 99% to 100%  prevention of hospitalization and death across their multiple trials in the United States.

Vaccines are first evaluated for safety and efficacy before they are approved for use. The World Health Organization estimates that only roughly 7% of total vaccine candidates studied on laboratory animals are moved into human clinical trials and only 20% of these are successful. The development of many different vaccines thus increases the probability of producing more successful and widely available ones. This heeds the need for further vaccine research and development, amplifying the prioritization of adequate provision of these medications to citizens, both locally and globally.

As the gaps in efficacy rates presented in various media platforms fuel people’s doubts about some vaccines, scientists argue that these numbers are incomparable with one another unless they are based on identical inclusion criteria. This can be said as the trials of different vaccines occurred in different time frames and locations. Infection rates thus vary according to the variants and number of cases present during the trials. Although these vaccines showed different efficacy rates, it must be emphasized that they all induce a near 100% protection from hospitalization and death. This goes to show that vaccination would ensure our survival and one of the key factors in ending this pandemic.