The long-term solution to Covid-19 and a return to normality lies, not in restrictions and lockdown, but in harnessing the body’s immune system to reject the virus and the induction of herd immunity.
Community or herd immunity is reached when a threshold of individuals in a population (more than 70 per cent) has developed protective immune responses through previous infection with the pathogen or through vaccination.
By eliminating the spread of the virus within the population, the development of herd immunity can protect the most vulnerable, including older individuals who may themselves not generate effective immune responses to the virus.
However, herd immunity to Sars-CoV-2 will be almost impossible to achieve through previous infection and is unlikely to be acceptable in most countries because of the associated death rate. The best chance of achieving low or no Covid-19 is through an effective vaccine.
In the last two weeks we have had news the whole world was waiting for, with Pfizer/BioNTech and Moderna announcing their Covid-19 vaccines are about 95 per cent effective at preventing Covid-19 disease.
In the last two weeks we have had news the whole world was waiting for
Results from the phase 3 trial of Oxford-Astra Zeneca vaccine are expected in the coming weeks and early indications are that it induces good immune responses in the elderly.
The Pfizer and Moderna vaccines utilise genetic material (messenger RNA) for the Sars-CoV-2 spike protein, whereas the Oxford-Astra Zeneca vaccine uses a weakened adenovirus that causes the common cold as vector for a spike protein gene that our cells will read and provoke protective immune responses.
Hard data
It is important, from a scientific perspective, to introduce a few notes of caution.
- No hard data on efficacy and safety has been provided by the vaccine manufacturers on the phase 3 clinical trials, only headline figures in press releases.
- The vaccine efficacy rate, 94.5 per cent and 95 per cent for the Moderna and Pfizer vaccines respectively, refer to protection against Covid-19 disease not against Sars-CoV-2 infection.
- The efficacy was estimated only seven days (Pfizer) or 14 days (Moderna) after the last of two vaccinations.
A Covid-19 vaccine that gives even short-term protection against disease would be useful in preventing hospitalisation and deaths from Covid-19. However, for the vaccine to be optimally useful, it needs to sustain protection for several years and it needs to prevent infection with Sars-CoV-2 as well as preventing Covid-19 disease.
We have learned from experience with other infectious diseases that vaccines that do not prevent infection may not prevent transmission of a virus or bacteria in the population. For example, the current pertussis vaccine prevents children from dying from whooping cough, but does not prevent bacterial colonisation of the nose, thus allowing community transmission of the infection, resulting in periodic epidemics of whooping cough.
Induction of sterilising immunity is the holy grail of vaccination. For a vaccine against Covid-19 to prevent community transmission of Sars-CoV-2, it needs to prevent infection of the nose and lungs. Data from pre-clinical studies with Covid-19 vaccine suggests this is achievable with some, but not other, Covid-19 vaccines. We keenly await the full data from the phase 3 clinical trials.
If candidate Covid-19 vaccines are licensed for general use, the logistics of storage, distribution, rollout and vaccination of the entire population will not be trivial.
The logistics of storage, distribution, rollout and vaccination of the entire population will not be trivial
Every country in the world wants these vaccines. Countries are placing each way bets to ensure they have backed one or more of the vaccine “winners”. The EU, UK and US already have advance purchase agreements in place with different manufactures, which are using different strategies to prepare their vaccine.
Emergence use authorisation
Pfizer and Moderna are expected to apply to the US Food and Drug Administration (FDA) for emergence use authorisation of their vaccines in the coming days, and a response is expected within weeks. The European Medicine Agency (EMA) also has a fast-tract approach to assessing Covid-19 vaccines.
If the efficacy and safety data pass the scrutiny of the regulatory agencies, we might see the first Covid-19 vaccines approved and in use by the end of the year.
The first recipients of the vaccines will be high-risk individuals and it may take some months for vaccines to be rolled out to the general population and even years to achieve herd immunity.
Ireland needs to have effective structures in place to successfully implement a population-wide vaccination programme; current structures are not optimal. The Health Service Executive, hospitals and GPs in Ireland do not have integrated IT systems and, unlike most developed countries, Ireland does not have a patient identifier number.
Scanning of barcodes on every vial of vaccine before administration coupled with a patient identifier number would allow electronic recording of every individual vaccination.
Now is the time for the Department of Health to tackle these deficiencies.
Vaccine safety is a key concern for many people and vaccine hesitancy especially with unproven approaches is a significant issue. Any concerns about adverse reactions in any age group will reduce public confidence, and reduce vaccine acceptance. To achieve vaccination uptake of over 70 per cent and herd immunity, transparent and accessible data on the risks versus the benefits of vaccination must be made available to the public.
Millions of lives
Vaccines have saved millions of lives globally each year and have eliminated smallpox and are close to eliminating poliovirus. Successful vaccination has dramatically reduced the incidence of diphtheria, tetanus, measles, mumps, rubella and haemophilus influenzae type B to close to zero in many developed countries. The human papilloma virus (HPV) vaccine is close to 100 per cent effective at preventing cervical cancer for more than 10 years.
Most vaccines have some side-effects, but the adverse reactions associated with Covid-19 vaccines in the published reports from the early clinical trials to date are self-limiting and include injection site reactions and temporary flu-like symptoms.
There is a huge sense of cautious optimism among immunologists and vaccinologists regarding the recent vaccine announcements. If one or more of the candidate Covid-19 vaccines is safe and effective and, importantly, embraced by communities, it will dispense with the need for restrictions and lockdowns and their devastating effects on our lives and economies and will eventually allow society to return to normality.
Kingston Mills is professor of experimental immunology and academic director of Trinity Biomedical Sciences Institute, Trinity College Dublin