The AstraZeneca clinical trials of the Oxford vaccine have been put on hold due to an unprecedented event. However, an expert in immunology explained that everyone has a unique immune response to a vaccine. The event might even help show the range of population groups that could be vaccinated.
The five factors that make immune responses to a vaccine unique were explained by immunology experts at Monash University. Every person would respond uniquely to a vaccine due to outstanding factors, including age, previous infections, genetics, and vaccine models. While most would respond positively, some might develop unusual reactions, including rare adverse events. They explained the factors in The Conversation, a not-for-profit media network.
The Vaccination Coverage Worldwide
Vaccines have been the best weapon of humanity against serious, contagious diseases. Without its discovery, millions of people would have died from vaccine-preventable diseases, such as measles and polio. Survivors would likely be suffering from life-long disability that could affect their quality of life and ability to work. Despite the low risk of side effects, vaccines remained critical in protecting children and adults from specific illnesses, which do not have a cure or definite treatment.
According to Statista, a German portal for statistics, several vaccines were widespread across the globe in 2018. The tuberculosis vaccine had the highest share of one-year-olds worldwide at 89%. It was followed by the tetanus/diphtheria/pertussis vaccine at 86%, polio vaccine at 85%, hepatitis B vaccine at 84%, Haemophilus influenzae vaccine at 72%, measles/rubella vaccine at 69%, yellow fever vaccine in 40 territories at 49%, pheumococcal disease vaccine at 47%, and rotavirus vaccine at 35%. The figures still showed that additional efforts in vaccination programs are needed to increase vaccine coverage.
Meanwhile, many people worldwide believed that vaccines are important in children in 2018. The survey conducted from April to December 2018 among 140,000 respondents revealed the agreement per region. Globally, 76% agreed that vaccines are needed by children. Around 85% in North Africa, 92% in Eastern Africa, 80% in Central Africa, 87% in Western Africa, 83% in Southern Africa, 74% in Northern America, 85% in Southern America, 89% in Central America and Mexico, 80% in Central Asia, 60% in East Asia, 89% in South Asia, 76% in Southeast Asia, 83% in the Middle East, 70% in Southern Europe, 75% in Northern Europe, 60% in Western Europe, 65% in Eastern Europe, and 82% in Australia and New Zealand agreed in vaccinating children.
Factors That Influence Unique Immune Responses to Vaccines
In this pandemic, several COVID-19 vaccine candidates are being tested either in preclinical or clinical trials. Some are already in late-stage human clinical trials, which involve tens of thousands of participants. But most of these vaccines contain portions of the coronavirus' spike protein to elicit an immune response. The immune system needs to recognize the spike protein to produce antibodies. This is how the vaccines prepares the human body for the wild SARS-CoV-2.
Unfortunately, every person is unique and one can react differently from another. No matter how constant the vaccine models are, the dynamics inside the body can alter the outcome. This is why vaccine makers attempt to optimize the formulation to significantly minimize adverse events. Paul Gill, a post-doctoral researcher in gastroenterology and immunology, and Menno van Zelm, an associate professor of immunology at Monash University, revealed the factors with roles in immune responses to vaccines.
The first factor is the vaccine type and its delivery route. Several COVID-19 vaccines need to expose the human body to the spike protein, but there are multiple ways to do that. One way is to introduce the spike protein using another virus, like in the Oxford vaccine. Another way is to mix it with an adjuvant to stimulate the immune system, like in the University of Queensland vaccine. Some developers are looking into nasal sprays to focus on the upper respiratory tract to lower side effects and maximize efficacy.
The second factor is previous infections fought by the immune system. The immune system can "memorize" previous pathogens encountered. In the context of COVID-19, the exposure to several other coronaviruses may result in multiple dedicated memory cells. That may stimulate the immune system quickly and better to a COVID-19 vaccine. This is because SARS-CoV-2 has a relationship with other coronaviruses. The immune system may use its memory of other coronaviruses in responding and learning this spike protein. Also, some people may have a weaker response to certain COVID-19 vaccines. If the vaccine contains an adenovirus strain as a vector, a person with immunity against that virus may not respond. Their immune system likely mounted on the vector, instead on the spike protein.
The third factor is genetics. Genes have a significant role in the functions of the immune system. Between genders, many studies have found that the immune systems in men and women react differently to infections. One gender may be more effective against influenza while the other is better in handling a different virus. This is applicable as well in people with genes linked to immune deficiencies or autoimmune disorders. The abnormalities in those genes can be predictors of immune responses from COVID-19 vaccines.
The fourth factor is the age of a person. Typically, the immune systems of babies and elderlies are weaker than young adults. But in some cases, the immune systems of young adults can be overreactive to an infection. In babies and children, the immune system is still developing and may respond differently, compared to adults. Yet certain vaccines like flu shots are better responded by children, which led to pediatric recommendations. Despite of age difference, some elderlies survived COVID-19 due to their immune systems being incredibly strong. Researchers recognize that exposure to other illnesses, for example SARS, may have resulted in an incredibly robust immune system.
And finally, the fifth factor is the lifestyle of an individual. Diet, stress, exercise, sleep, smoking, and drinking play a part in the immune system. For basics, a person who suffers from chronic sleep deprivation likely has a weaker immune system. They can easily catch the common cold and unable to shake it off quickly, compared to a person with adequate sleep. Lifestyle factors can either enhance or damage the immune system. Also, diet defines the bacterial populations in the gut. Beneficial bacteria can help the immune system against infections. This makes them possible influencers to vaccine response.
The investigation of the unexpected adverse event from the Oxford vaccine is ongoing. Investigators are checking if the event is due to the vaccine or the placebo. There is no official diagnosis yet for the complication.