Experts say herd immunity will control covid-19 infections

A number of health experts stress the importance of vaccinating a certain percentage of the population in the fight against the coronavirus.

Dr Jeremiah Gitau Ngenga, the chair Covid-19 champions’ response team at Kenyatta University Teaching, Referral and Research Hospital in Nairobi, Kenya, says this exercise will effectively give the population herd immunity.

According to Dr Gitau, herd immunity also known as population immunity is the indirect protection from an infectious disease that happens when the body develops immunity in a population either through vaccination or through previous infection. It does not mean unvaccinated or individuals who have not previously been infected are themselves immune.

Instead, it exists when individuals who are not immune but live in a community with a high proportion of immunity have a reduced risk of the disease as compared to non-immune individuals living in a community with a small proportion of immunity.

Herd immunity is an important attribute of vaccines against polio, rotavirus, pneumococcus, Haemophilus influenz, yellow fever, meningococcus and numerous other vaccine preventable diseases.

Herd immunity makes it possible to protect the population from a disease, including those who cannot be vaccinated, such as newborns or those who have compromised immune systems.

Using the concept of herd immunity, vaccines have successfully controlled deadly contagious diseases such as smallpox, polio, diphtheria, rubella and many others.

Uganda’s case
In Uganda, the Ministry of health received 864,000 doses of the AstraZeneca vaccine on March 5 from the COVAX facility, which is the world’s facility for universal access to Covid-19 vaccines.

The arrival marked a historic step towards ensuring equitable distribution of Covid-19 vaccines globally, in an effort to provide at least two billion doses by the end of 2021.

The vaccine was received at Entebbe International Airport by Uganda’s Health Minister, Dr Jane Ruth Aceng accompanied by members of the COVAX Facility and ambassadors of the European Union.

According reports, Uganda targets to vaccinate 49.6 per cent of the population, which is about 21,936,011 in a phased manner. Each phase is planned to cover 20 per cent of the population, which is approximately 4.38 million people.  

Uganda received 3,552,000 doses of the AstraZeneca vaccine the remaining 2,688,000 doses are expected by June 2021.

Target groups
The first phase of the free vaccination will target health workers in public and private health facilities who by the nature of their work are at higher risk of contracting the disease compared to other categories of people.

Other target groups in order of priority are security personnel, teachers, humanitarian front-line workers, people above 50 years with underlying conditions such as diabetes, hypertension, heart, kidney, or liver disease; people aged 18-50 with the same underlying conditions and other emerging high risk and priority essential groups as more vaccine doses arrive in the country.

How are vaccines developed?

Dr Gitau and team contend there are various vaccine types which are developed using the same procedure but with use of different pathogen as explained below.

Some are created by reducing virulence of vaccine pathogens (attenuated vaccines) where scientists alter the infection agent to make it harmless.

Killed pathogens (live vaccines) are derived from wild disease-causing, viruses or bacteria. They are weakened, in a laboratory, usually by repeated culturing.

For example, the measles virus used as a vaccine today was isolated from a child with measles disease in 1954.

Part of pathogens (particle vaccines): Human Papillomavirus Vaccine the current papillomavirus (HPV) vaccines are example of pathogen vaccines.

They are prophylactic virus-like particle vaccines that consist of recombinant capsid proteins introduced in virus like particles that are noninfectious. They produce high levels of neutralizing antibodies.
Genetic material of pathogen such as RNA, DNA (Nucleic acid vaccines):

Depending on the vaccine, the genetic material could be DNA or RNA, in both cases it provides the instructions for making a specific protein from the pathogen.

Genetic material of pathogen in delivery vehicle (vectored vaccines): This is developed using advanced gene editing technology using gene therapy.

Here scientists use Nucleic acids and their analogs which have many therapeutic applications, ranging from correction of genetic defects to gene increase for chronic diseases including cancer to acting as adjuvants for vaccination.
 
Vaccine testing
Usually, scientists start with preclinical trials where testing is done in the laboratory on mice and apes before moving into clinical trials.

Clinical trials are in four phases. In phase one, scientists want to establish if the vaccine is safe and this is done by testing on small numbers of humans, usually 10 people.

Phase II involves testing whether the vaccine produces immune response in humans and the dose is usually given to 100 people or more.

In Phase III, there is testing to see if the immune response is protecting humans from infection. The efficacy trials are tested on 1,000 persons or more.

Phase IV  is where scientists establish  how well the vaccine is working in the population and this is where post marketing surveillance is done for registration ready to be rolled out.

What to consider before administering covid-19 vaccine
● One should go to an immunising health facility where they have been registered for vaccination and present evidence of registration.
● Ensure the persons are among the target groups at the time and had not been vaccinated against Covid-19 before.
● Ensure they have no fever with temperature currently below 38°C and no reported allergies.
● Ensure they have not suffered Covid-19 infection within the last six months preceding the day for vaccination.
● Ensure they are not pregnant or breastfeeding at the time of vaccination. However, a pregnancy test will not be required since verbal or written consent will suffice.

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