Across the world, COVID-19 vaccination programmes have been rolled out. According to ourworldindata.org, over 541 million doses of COVID-19 vaccines have been administered.
Health experts believe vaccination is one of the assured means to prevent and control the spread of the SARS-Cov-2, the virus that causes the Coronavirus disease.
Ghana received its first batch of vaccines through the United Nations-backed COVAX initiative in late February, and according to President Akufo-Addo, about 500,000 Ghanaians have so far been vaccinated. Other countries in Africa have subsequently received vaccine doses under the COVAX initiative and have rolled vaccination programmes.
Health experts maintain that to effectively limit the spread of the virus among any group of people through vaccination, the population must reach herd immunity. But what does that mean?
In this report, Fact-check Ghana looks into what vaccination entails and what it means to attain herd immunity. The report also explores how and when Ghana is expected to achieve its immunity target.
Meaning of vaccination and its purpose
Vaccination is the injection of a killed microbe, the organism that causes a particular disease, to stimulate the immune system against the microbe, thereby preventing disease. The purpose of a vaccine according to the US Centre for Disease Control and Prevention (CDC) stimulates the immune system to produce antibodies, exactly like it would if one was exposed to the disease.
According to the World Health Organsiation (WHO), vaccines train the immune system to create proteins that fight diseases, known as ‘antibodies’, just as would happen when one is exposed to a disease. However, vaccines work without making one sick. Vaccinated people are protected from getting the disease in question and passing on the pathogen, breaking any chains of transmission.
After getting vaccinated, one develops immunity to that disease, without having to get the disease first. Unlike most medicines, which treat or cure diseases, vaccines prevent them.
After mass vaccination of the population, herd immunity is attained to prevent the entire population from contracting the virus.
What is herd immunity?
Herd immunity, also known as population immunity, is the indirect protection from an infectious disease that happens when a population is immune either through vaccination or immunity developed through a previous infection.
The WHO supports achieving ‘herd immunity’ through vaccination, rather than allowing the disease to spread through any segment of the population, as this would result in unnecessary cases and deaths.
To safely achieve herd immunity against COVID-19, a substantial proportion of a population would need to be vaccinated, lowering the overall amount of virus able to spread in the whole population. Achieving herd immunity helps to keep vulnerable groups who cannot get vaccinated (e.g. due to health conditions like allergic reactions to the vaccine) safe and protected from the disease.
The percentage of people who need to be immune to achieve herd immunity varies with each disease. For example, according to WHO, herd immunity against measles requires about 95% of a population to be vaccinated. The remaining 5% will be protected by the fact that measles will not spread among those who are vaccinated. For polio, the threshold is about 80%.
The proportion of the population that must be vaccinated against COVID-19 to begin inducing herd immunity, according to WHO, is not known yet. This is an important area of research and will likely vary according to the community, the vaccine, the populations prioritised for vaccination, and other factors. Achieving herd immunity with safe and effective vaccines makes diseases rarer and saves lives.
Natural herd immunity is dangerous and problematic
To reach herd immunity by allowing people to be infected with the virus is scientifically problematic and unethical. Letting COVID-19 spread through populations, of any age or health status, will lead to unnecessary infections, suffering and death.
The vast majority of people in most countries remain susceptible to this virus. Seroprevalence surveys suggest that in most countries, less than 10% of the population have been infected with the virus.
The survey shows most people who are infected with COVID-19 develop an immune response within the first few weeks, but there is no known fact on how strong or lasting that immune response is, or how it differs for different people. There have also been reports of people infected with COVID-19 for a second time.
Until COVID-19 immunity is better understood, it will not be possible to know how much of a population is immune and how long that immunity lasts, let alone make future predictions. These challenges should preclude any plans that try to increase immunity within a population by allowing people to get infected. Although older people and those with underlying conditions are most at risk of severe disease and death, they are not the only ones at risk.
Also, while most infected people get mild or moderate forms of COVID-19 and some experience no sickness, many become seriously ill and get admitted to a hospital.
According to the WHO, the long-term health impacts among people who have had the virus is yet to be fully understood, including what is being described as ‘Long Covid.’ WHO is working with clinicians and patient groups to better understand the long term effects of COVID-19.
For other coronaviruses – such as the common cold, SARS-CoV-1 and Middle East Respiratory Syndrome (MERS) – immunity declines over time, as is the case with other diseases. While people infected with the SARS-CoV-2 virus develop antibodies and immunity, whose lasting duration is not yet known.
How and when will Ghana attain herd immunity?
Fact-Check Ghana enquired from the Ghana Health Service (GHS) how and when Ghana will attain herd immunity, especially when the WHO has established there is more to learn when it comes to COVID-19 immunity.
The Manager of the Expanded Programme on Immunisation at the GHS, Dr. Kwame Amponsa-Achiano, indicated that by the close of December, Ghana can attain herd immunity to protect the population. However, he added that the success of the target highly thrives on the availability of vaccines.
“We targeted October to maximum December. Traditionally, we could complete vaccination within two weeks maximum but looking at the enormity or quantum of people, if we had all vaccines, we could do this campaign in a maximum of two months, but because we know that we are not going to get vaccines in large quantities unlike previously when we were doing polio and yellow fever [vaccination], that is why we’ve given ourselves a long period from March to October/December, which is almost nine months. So on paper, by October but we are looking at end of November. In fact, it all depends on the availability of vaccines,” he explained.
He further noted that even though “nobody really knows what the herd immunity threshold is, 20 million Ghanaians need to be vaccinated to attain a herd immunity, which is 64% to 65% of the population.”
He added that there are a lot of models that suggest the immunity threshold is around 60% with some quoting around 75%, “but we are comfortable that if you are able to get 60% that will be awesome and we are likely to hit the population of herd immunity.”
This report is produced under the project: COVID-19 Response in Africa: Together for Reliable Information being implemented with funding support from the European Union.